(* Copyright (c) 2015-present, Facebook, Inc.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *  Forked from OCaml, which is provided under the license below:
 *
 *  Xavier Leroy, projet Cristal, INRIA Rocquencourt
 *
 *  Copyright © 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Inria
 *
 *  Permission is hereby granted, free of charge, to the Licensee obtaining a
 *  copy of this software and associated documentation files (the "Software"),
 *  to deal in the Software without restriction, including without limitation
 *  the rights to use, copy, modify, merge, publish, distribute, sublicense
 *  under any license of the Licensee's choice, and/or sell copies of the
 *  Software, subject to the following conditions:
 *
 *  1.	Redistributions of source code must retain the above copyright notice
 *  and the following disclaimer.
 *  2.	Redistributions in binary form must reproduce the above copyright
 *  notice, the following disclaimer in the documentation and/or other
 *  materials provided with the distribution.
 *  3.	All advertising materials mentioning features or use of the Software
 *  must display the following acknowledgement: This product includes all or
 *  parts of the Caml system developed by Inria and its contributors.
 *  4.	Other than specified in clause 3, neither the name of Inria nor the
 *  names of its contributors may be used to endorse or promote products
 *  derived from the Software without specific prior written permission.
 *
 *  Disclaimer
 *
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 *  or implied warranties, including, but not limited to, the implied
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*)

(* TODO more fine-grained precedence pretty-printing *)

module Easy_format = Vendored_easy_format
open Ppxlib
open Easy_format
module Comment = Reason_comment
module Layout = Reason_layout
module WhitespaceRegion = Layout.WhitespaceRegion
module Range = Reason_location.Range

let source_map = Layout.source_map

exception NotPossible of string

let commaTrail =
  Layout.SepFinal (",", Reason_syntax_util.TrailingCommaMarker.string)

let commaSep = Layout.Sep ","

type ruleInfoData =
  { reducePrecedence : precedence
  ; shiftPrecedence : precedence
  }

and ruleCategory =
  (* Printing will be parsed with very high precedence, so not much need to
     worry about ensuring it will reduce correctly. In short, you can put
     `FunctionApplication` content anywhere around an infix identifier without
     wrapping in parens. For example `myFunc x y z` or `if x {y} else {z}` The
     layout is kept in list form only to allow for elegant wrapping rules to
     take into consideration the *number* of high precedence parsed items. *)
  | FunctionApplication of Layout.t list
  (* Care should be taken to ensure the rule that caused it to be parsed will
     reduce again on the printed output - context should carefully consider
     wrapping in parens according to the ruleInfoData. *)
  | SpecificInfixPrecedence of ruleInfoData * resolvedRule
  (* Not safe to include anywhere between infix operators without wrapping in
     parens. This describes expressions like `fun x => x` which doesn't fit into
     our simplistic algorithm for printing function applications separated by
     infix.

     It might be possible to include these in between infix, but there are
     tricky rules to determining when these must be guarded by parens (it
     depends highly on context that is hard to reason about). It's so nuanced
     that it's easier just to always wrap them in parens. *)
  | PotentiallyLowPrecedence of Layout.t
  (* Simple means it is clearly one token (such as (anything) or [anything] or
     identifier *)
  | Simple of Layout.t

(* Represents a ruleCategory where the precedence has been resolved.
 * The precedence of a ruleCategory gets resolved in `ensureExpression` or
 * `ensureContainingRule`. The result is either a plain Layout.t (where
 * parens probably have been applied) or an InfixTree containing the operator and
 * a left & right resolvedRule. The latter indicates that the precedence has been resolved,
 * but the actual formatting is deferred to a later stadium.
 * Think `let x = foo |> f |> z |>`, which requires a certain formatting style when
 * things break over multiple lines. *)
and resolvedRule =
  | LayoutNode of Layout.t
  | InfixTree of string * resolvedRule * resolvedRule

and associativity =
  | Right
  | Nonassoc
  | Left

and precedenceEntryType =
  | TokenPrecedence
  | CustomPrecedence

and precedence =
  | Token of string
  | Custom of string

(* Describes the "fixity" of a token, and stores its *printed* representation
   should it be rendered as infix/prefix (This rendering may be different than
   how it is stored in the AST). *)
and tokenFixity =
  (* Such as !simple_expr and ~!simple_expr. These function applications are
     considered *almost* "simple" because they may be allowed anywhere a simple
     expression is accepted, except for when on the left hand side of a
     dot/send. *)
  | AlmostSimplePrefix of string
  | UnaryPlusPrefix of string
  | UnaryMinusPrefix of string
  | UnaryNotPrefix of string
  | UnaryPostfix of string
  | Infix of string
  | Letop of string
  | Andop of string
  | Normal

(* Type which represents a resolvedRule's InfixTree flattened *)
type infixChain =
  | InfixToken of string
  | Layout of Layout.t

(* Helpers for dealing with extension nodes (%expr) *)

let expression_extension_sugar x =
  if x.pexp_attributes != []
  then None
  else
    match x.pexp_desc with
    | Pexp_extension (name, PStr [ { pstr_desc = Pstr_eval (expr, []); _ } ])
      when name.txt <> "mel.obj" ->
      Some (name, expr)
    | _ -> None

let expression_immediate_extension_sugar x =
  match expression_extension_sugar x with
  | None -> None, x
  | Some (name, expr) ->
    (match expr.pexp_desc with
    | Pexp_for _ | Pexp_while _ | Pexp_ifthenelse _ | Pexp_function _
    | Pexp_newtype _ | Pexp_try _ | Pexp_match _ ->
      Some name, expr
    | _ -> None, x)

let expression_not_immediate_extension_sugar x =
  match expression_immediate_extension_sugar x with
  | Some _, _ -> None
  | None, _ -> expression_extension_sugar x

let add_extension_sugar keyword = function
  | None -> keyword
  | Some str -> keyword ^ "%" ^ str.txt

let override = function Override -> "!" | Fresh -> ""

let add_open_extension_sugar ~override:open_override extension =
  let base = "open" in
  match extension, open_override with
  | extension, Fresh -> add_extension_sugar base extension
  | None, Override -> base ^ override open_override
  | Some _, Override ->
    (* need to add a space between `!` and `%foo` otherwise it can't be parsed
       back *)
    add_extension_sugar (base ^ override open_override ^ " ") extension

let string_equal : string -> string -> bool = ( = )

let string_loc_equal : string Asttypes.loc -> string Asttypes.loc -> bool =
 fun l1 l2 -> l1.txt = l2.txt

let longident_same l1 l2 =
  let rec equal l1 l2 =
    match l1, l2 with
    | Lident l1, Lident l2 -> string_equal l1 l2
    | Ldot (path1, l1), Ldot (path2, l2) ->
      equal path1 path2 && string_equal l1 l2
    | Lapply (l11, l12), Lapply (l21, l22) -> equal l11 l21 && equal l12 l22
    | _ -> false
  in
  equal l1.txt l2.txt

(* A variant of List.for_all2 that returns false instead of failing on lists of
   different size *)
let for_all2' pred l1 l2 = try List.for_all2 pred l1 l2 with _ -> false

(* Checks to see if two types are the same modulo the process of varification
   which turns abstract types into type variables of the same name. For example,
   [same_ast_modulo_varification] would consider (a => b) and ('a => 'b) to have
   the same ast. This is useful in recovering syntactic sugar for explicit
   polymorphic types with locally abstract types.

   Does not compare attributes, or extensions intentionally.

   TODO: This has one more issue: We need to compare only accepting t1's type
   variables, to be considered compatible with t2's type constructors - not the
   other way around. *)
let same_ast_modulo_varification_and_extensions t1 t2 =
  let rec loop t1 t2 =
    match t1.ptyp_desc, t2.ptyp_desc with
    (* Importantly, cover the case where type constructors (of the form [a]) are
       converted to type vars of the form ['a]. *)
    | Ptyp_constr ({ txt = Lident s1; _ }, []), Ptyp_var s2 ->
      string_equal s1 s2
    (* Now cover the case where type variables (of the form ['a]) are converted
       to type constructors of the form [a]. *)
    | Ptyp_var s1, Ptyp_constr ({ txt = Lident s2; _ }, []) ->
      string_equal s1 s2
    (* Now cover the typical case *)
    | Ptyp_constr (longident1, lst1), Ptyp_constr (longident2, lst2) ->
      longident_same longident1 longident2 && for_all2' loop lst1 lst2
    | Ptyp_any, Ptyp_any -> true
    | Ptyp_var x1, Ptyp_var x2 -> string_equal x1 x2
    | ( Ptyp_arrow (label1, core_type1, core_type1')
      , Ptyp_arrow (label2, core_type2, core_type2') ) ->
      (match label1, label2 with
        | Nolabel, Nolabel -> true
        | Labelled s1, Labelled s2 -> string_equal s1 s2
        | Optional s1, Optional s2 -> string_equal s1 s2
        | _ -> false)
      && loop core_type1 core_type2
      && loop core_type1' core_type2'
    | Ptyp_tuple lst1, Ptyp_tuple lst2 -> for_all2' loop lst1 lst2
    | Ptyp_object (lst1, o1), Ptyp_object (lst2, o2) ->
      let tester t1 t2 =
        match t1.pof_desc, t2.pof_desc with
        | Otag (s1, t1), Otag (s2, t2) ->
          string_equal s1.txt s2.txt && loop t1 t2
        | Oinherit t1, Oinherit t2 -> loop t1 t2
        | _ -> false
      in
      for_all2' tester lst1 lst2 && o1 = o2
    | Ptyp_class (longident1, lst1), Ptyp_class (longident2, lst2) ->
      longident_same longident1 longident2 && for_all2' loop lst1 lst2
    | Ptyp_alias (core_type1, string1), Ptyp_alias (core_type2, string2) ->
      loop core_type1 core_type2 && string_equal string1 string2
    | ( Ptyp_variant (row_field_list1, flag1, lbl_lst_option1)
      , Ptyp_variant (row_field_list2, flag2, lbl_lst_option2) ) ->
      for_all2' rowFieldEqual row_field_list1 row_field_list2
      && flag1 = flag2
      && lbl_lst_option1 = lbl_lst_option2
    | Ptyp_poly (string_lst1, core_type1), Ptyp_poly (string_lst2, core_type2)
      ->
      for_all2' string_loc_equal string_lst1 string_lst2
      && loop core_type1 core_type2
    | Ptyp_package (longident1, lst1), Ptyp_package (longident2, lst2) ->
      longident_same longident1 longident2
      && for_all2' testPackageType lst1 lst2
    | Ptyp_extension (s1, _), Ptyp_extension (s2, _) ->
      string_equal s1.txt s2.txt
    | _ -> false
  and testPackageType (lblLongIdent1, ct1) (lblLongIdent2, ct2) =
    longident_same lblLongIdent1 lblLongIdent2 && loop ct1 ct2
  and rowFieldEqual f1 f2 =
    match f1.prf_desc, f2.prf_desc with
    | Rtag (label1, flag1, lst1), Rtag (label2, flag2, lst2) ->
      string_equal label1.txt label2.txt
      && flag1 = flag2
      && for_all2' loop lst1 lst2
    | Rinherit t1, Rinherit t2 -> loop t1 t2
    | _ -> false
  in
  loop t1 t2

let expandLocation pos ~expand:(startPos, endPos) =
  { pos with
    loc_start =
      { pos.loc_start with
        Lexing.pos_cnum = pos.loc_start.Lexing.pos_cnum + startPos
      }
  ; loc_end =
      { pos.loc_end with
        Lexing.pos_cnum = pos.loc_end.Lexing.pos_cnum + endPos
      }
  }

(* Computes the location of the attribute with the lowest line number
 * that isn't ghost. Useful to determine the start location of an item
 * in the parsetree that has attributes.
 * If there are no valid attributes, defaults to the passed location.
 * 1| [@attr]           --> notice how the "start" is determined
 * 2| let f = ...           by the attr on line 1, not the lnum of the `let`
*)
let rec firstAttrLoc loc = function
  | ({ attr_name = attrLoc; _ } : Parsetree.attribute) :: attrs ->
    if
      attrLoc.loc.loc_start.pos_lnum < loc.loc_start.pos_lnum
      && not attrLoc.loc.loc_ghost
    then firstAttrLoc attrLoc.loc attrs
    else firstAttrLoc loc attrs
  | [] -> loc

let extractLocationFromValBindList expr vbs =
  let rec extract loc = function
    | x :: xs ->
      let { pvb_expr; _ } = x in
      let loc = { loc with loc_end = pvb_expr.pexp_loc.loc_end } in
      extract loc xs
    | [] -> loc
  in
  let loc =
    match vbs with
    | x :: xs ->
      let { pvb_pat; pvb_expr; _ } = x in
      let loc = { pvb_pat.ppat_loc with loc_end = pvb_expr.pexp_loc.loc_end } in
      extract loc xs
    | [] -> expr.pexp_loc
  in
  { loc with loc_start = expr.pexp_loc.loc_start }

let extractLocValBinding { pvb_pat; pvb_expr; pvb_attributes; _ } =
  let estimatedLoc = firstAttrLoc pvb_pat.ppat_loc pvb_attributes in
  { estimatedLoc with loc_end = pvb_expr.pexp_loc.loc_end }

let extractLocBindingOp { pbop_pat; pbop_exp; _ } =
  let estimatedLoc = firstAttrLoc pbop_pat.ppat_loc [] in
  { estimatedLoc with loc_end = pbop_exp.pexp_loc.loc_end }

let extractLocModuleBinding { pmb_expr; pmb_attributes; _ } =
  let estimatedLoc = firstAttrLoc pmb_expr.pmod_loc pmb_attributes in
  { estimatedLoc with loc_end = pmb_expr.pmod_loc.loc_end }

let extractLocModDecl { pmd_type; pmd_attributes; _ } =
  let estimatedLoc = firstAttrLoc pmd_type.pmty_loc pmd_attributes in
  { estimatedLoc with loc_end = pmd_type.pmty_loc.loc_end }

let rec sequentialIfBlocks x =
  match x with
  | Some { pexp_desc = Pexp_ifthenelse (e1, e2, els); _ } ->
    let nestedIfs, finalExpression = sequentialIfBlocks els in
    (e1, e2) :: nestedIfs, finalExpression
  | Some e -> [], Some e
  | None -> [], None

(* TODO: IDE integration beginning with Vim:
 *
 * - Create recovering version of parser that creates regions of "unknown"
 *   content in between let sequence bindings (anything between semicolons,
 *   really).
 * - Use Easy_format's "style" features to tag each known node.
 * - Turn those style annotations into editor highlight commands.
 * - Editors have a set of keys that retrigger the parsing/rehighlighting
 *   process (typically newline/semi/close-brace).
 * - On every parsing/rehighlighting, this pretty printer can be used to
 *   determine the highlighting of recovered regions, and the editor plugin can
 *   relegate highlighting of malformed regions to the editor which mostly does
 *   so based on token patterns.
 *
*)

(* @avoidSingleTokenWrapping
 *
 *  +-----------------------------+
 *  |+------+                     |     Another label
 *  || let ( \                    |
 *  ||    a  | Label              |
 *  ||    o  |                    |     The thing to the right of any label must be a
 *  ||    p _+ label RHS          |     list in order for it to wrap correctly. Lists
 *  ||  ): /   v                  |     will wrap if they need to/can. NON-lists will
 *  |+--+ sixteenTuple = echoTuple|(    wrap (indented) even though they're no lists!
 *  +---/ 0,\---------------------+     To prevent a single item from wrapping, make
 *        0,                            an unbreakable list via ensureSingleTokenSticksToLabel.
 *        0
 *      );
 *  In general, the best approach for indenting
 *  let bindings is to keep building up labels from
 *  the "let", always ensuring things that you want
 *  to wrap will either be lists or guarded in
 *  [ensureSingleTokenSticksToLabel].
 *  If you must join several lists together (via =)
 *  (or colon), ensure that joining is done via
 *  [makeList] (which won't break), and that new
 *  list is always appended to the left
 *  hand side of the label. (So that the right hand
 *  side may always be the untouched list that you want
 *  to wrap with aligned closing).
 *  Always make sure rhs of the label are the
 *
 *  Creating nested labels will preserve the original
 *  indent location ("let" in this
 *  case) as long as that nesting is
 *  done on the left hand side of the labels.
 *
*)

(*  Table 2.1. Precedence and associativity.
 *  Precedence from highest to lowest: From RWOC, modified to include !=
 *  ---------------------------------------
 *
 *  Operator prefix	Associativity
 *  !..., ?..., ~...	                              Prefix
 *  ., .(, .[	-
 *  function application, constructor, assert, lazy	Left associative
 *  -, -.                                           Prefix
 *  **..., lsl, lsr, asr                            Right associative
 *  *..., /..., %..., mod, land, lor, lxor          Left associative
 *  +..., -...                                      Left associative
 *  ::                                              Right associative
 *  @..., ^...                                      Right associative
 *
 *  !=                                              Left associative (INFIXOP0 listed first in lexer)
 *  =..., <..., >..., |..., &..., $...              Left associative (INFIXOP0)
 *  =, <, >                                         Left associative (IN SAME row as INFIXOP0 listed after)
 *
 *  &, &&                                           Right associative
 *  or, ||                                          Right associative
 *  ,                                               -
 *  :=, =                                         	Right associative
 *  if                                              -
 *  ;                                               Right associative
 *
 *
 * Note: It would be much better if &... and |... were in separate precedence
 * groups just as & and | are. This way, we could encourage custom infix
 * operators to use one of the two precedences and no one would be confused as
 * to precedence (leading &, | are intuitive). Two precedence classes for the
 * majority of infix operators is totally sufficient.
 *
 * TODO: Free up the (&) operator from pervasives so it can be reused for
 * something very common such as string concatenation or list appending.
 *
 * let x = tail & head;
*)

(* "Almost Simple Prefix" function applications parse with the rule:

   `PREFIXOP simple_expr %prec below_DOT_AND_SHARP`, which in turn is almost
   considered a "simple expression" (it's acceptable anywhere a simple
   expression is except in a couple of edge cases.

   "Unary Prefix" function applications parse with the rule:

   `MINUS epxr %prec prec_unary_minus`, which in turn is considered an
   "expression" (not simple). All unary operators are mapped into an identifier
   beginning with "~".

   TODO: Migrate all "almost simple prefix" to "unsary prefix". When `!` becomes
   "not", then it will make more sense that !myFunc (arg) is parsed as !(myFunc
   arg) instead of (!myFunc) arg. *)
let almost_simple_prefix_symbols = [ '!'; '?'; '~' ]

(* Subset of prefix symbols that have special "unary precedence" *)
let unary_minus_prefix_symbols = [ "~-"; "~-." ]
let unary_plus_prefix_symbols = [ "~+"; "~+." ]

let infix_symbols =
  [ '='; '<'; '>'; '@'; '^'; '|'; '&'; '+'; '-'; '*'; '/'; '$'; '%'; '\\'; '#' ]

(* this should match "kwdopchar" from reason_declarative_lexer.mll *)
let special_infix_strings =
  [ "asr"; "land"; "lor"; "lsl"; "lsr"; "lxor"; "mod"; "or"; ":="; "!="; "!==" ]

let updateToken = "="
let sharpOpEqualToken = "#="
let pipeFirstToken = "->"
let requireIndentFor = [ updateToken; ":=" ]
let namedArgSym = "~"

let requireNoSpaceFor tok =
  tok = pipeFirstToken || (tok.[0] = '#' && tok <> "#=")

let funToken = "fun"

let getPrintableUnaryIdent s =
  if
    List.mem s unary_minus_prefix_symbols
    || List.mem s unary_plus_prefix_symbols
  then String.sub s 1 (String.length s - 1)
  else s

(* determines if the string is an infix string. checks backwards, first allowing
   a renaming postfix ("_102") which may have resulted from Pexp -> Texp -> Pexp
   translation, then checking if all the characters in the beginning of the
   string are valid infix characters. *)
let printedStringAndFixity = function
  | s when List.mem s special_infix_strings -> Infix s
  | "^" -> UnaryPostfix "^"
  | s when List.mem s.[0] infix_symbols -> Infix s
  (* Correctness under assumption that unary operators are stored in AST with
     leading "~" *)
  | s
    when List.mem s.[0] almost_simple_prefix_symbols
         && (not (List.mem s special_infix_strings))
         && not (s = "?") ->
    if
      (* What *kind* of prefix fixity? *)
      List.mem s unary_plus_prefix_symbols
    then UnaryPlusPrefix (getPrintableUnaryIdent s)
    else if List.mem s unary_minus_prefix_symbols
    then UnaryMinusPrefix (getPrintableUnaryIdent s)
    else if s = "!"
    then UnaryNotPrefix s
    else AlmostSimplePrefix s
  | s when Reason_syntax_util.is_letop s -> Letop s
  | s when Reason_syntax_util.is_andop s -> Andop s
  | _ -> Normal

(* Also, this doesn't account for != and !== being infixop!!! *)
let isSimplePrefixToken s =
  match printedStringAndFixity s with
  | AlmostSimplePrefix _ | UnaryPostfix "^" -> true
  | _ -> false

(* Convenient bank of information that represents the parser's precedence
   rankings. Each instance describes a precedence table entry. The function
   tests either a token string encountered by the parser, or (in the case of
   `CustomPrecedence`) the string name of a custom rule precedence declared
   using %prec *)
let rules =
  [ [ (TokenPrecedence, fun s -> Left, s = pipeFirstToken)
    ; ( TokenPrecedence
      , fun s -> Left, s.[0] = '#' && s <> sharpOpEqualToken && s <> "#" )
    ; (TokenPrecedence, fun s -> Left, s = ".")
    ; (CustomPrecedence, fun s -> Left, s = "prec_lbracket")
    ]
  ; [ (CustomPrecedence, fun s -> Nonassoc, s = "prec_functionAppl") ]
  ; [ (TokenPrecedence, fun s -> Right, isSimplePrefixToken s) ]
  ; [ (TokenPrecedence, fun s -> Left, s = sharpOpEqualToken) ]
  ; [ (CustomPrecedence, fun s -> Nonassoc, s = "prec_unary") ]
  ; (* Note the special case for "*\*", BARBAR, and LESSMINUS, AMPERSAND(s) *)
    [ (TokenPrecedence, fun s -> Right, s = "**")
    ; ( TokenPrecedence
      , fun s ->
          ( Right
          , String.length s > 1 && s.[0] == '*' && s.[1] == '\\' && s.[2] == '*'
          ) )
    ; (TokenPrecedence, fun s -> Right, s = "lsl")
    ; (TokenPrecedence, fun s -> Right, s = "lsr")
    ; (TokenPrecedence, fun s -> Right, s = "asr")
    ]
  ; [ ( TokenPrecedence
      , fun s -> Left, s.[0] == '*' && (String.length s == 1 || s != "*\\*") )
    ; (TokenPrecedence, fun s -> Left, s.[0] == '/')
    ; (TokenPrecedence, fun s -> Left, s.[0] == '%')
    ; (TokenPrecedence, fun s -> Left, s = "mod")
    ; (TokenPrecedence, fun s -> Left, s = "land")
    ; (TokenPrecedence, fun s -> Left, s = "lor")
    ; (TokenPrecedence, fun s -> Left, s = "lxor")
    ]
  ; [ (* Even though these use the same *tokens* as unary plus/minus at parse
         time, when unparsing infix -/+, the CustomPrecedence rule would be
         incorrect to use, and instead we need a rule that models what infix
         parsing would use - just the regular token precedence without a custom
         precedence. *)
      ( TokenPrecedence
      , fun s ->
          ( Left
          , if String.length s > 1 && s.[0] == '+' && s.[1] == '+'
            then
              (* Explicitly call this out as false because the other ++ case
                 below should have higher *lexing* priority. ++operator_chars*
                 is considered an entirely different token than
                 +(non_plus_operator_chars)* *)
              false
            else s.[0] == '+' ) )
    ; (TokenPrecedence, fun s -> Left, s.[0] == '-' && s <> pipeFirstToken)
    ; (TokenPrecedence, fun s -> Left, s = "!")
    ]
  ; [ (TokenPrecedence, fun s -> Right, s = "::") ]
  ; [ (TokenPrecedence, fun s -> Right, s.[0] == '@')
    ; (TokenPrecedence, fun s -> Right, s.[0] == '^')
    ; ( TokenPrecedence
      , fun s -> Right, String.length s > 1 && s.[0] == '+' && s.[1] == '+' )
    ]
  ; [ ( TokenPrecedence
      , fun s -> Left, s.[0] == '=' && (not (s = "=")) && not (s = "=>") )
    ; (TokenPrecedence, fun s -> Left, s.[0] == '<' && not (s = "<"))
    ; (TokenPrecedence, fun s -> Left, s.[0] == '>' && not (s = ">"))
    ; (TokenPrecedence, fun s -> Left, s = "!=")
    ; (* Not preset in the RWO table! *)
      (TokenPrecedence, fun s -> Left, s = "!==")
    ; (* Not preset in the RWO table! *)
      (TokenPrecedence, fun s -> Left, s = "==")
    ; (TokenPrecedence, fun s -> Left, s = "===")
    ; (TokenPrecedence, fun s -> Left, s = "<")
    ; (TokenPrecedence, fun s -> Left, s = ">")
    ; (TokenPrecedence, fun s -> Left, s.[0] == '|' && not (s = "||"))
    ; ( TokenPrecedence
      , fun s -> Left, s.[0] == '&' && (not (s = "&")) && not (s = "&&") )
    ; (TokenPrecedence, fun s -> Left, s.[0] == '$')
    ]
  ; [ (CustomPrecedence, fun s -> Left, s = funToken) ]
  ; [ (TokenPrecedence, fun s -> Right, s = "&")
    ; (TokenPrecedence, fun s -> Right, s = "&&")
    ]
  ; [ (TokenPrecedence, fun s -> Right, s = "or")
    ; (TokenPrecedence, fun s -> Right, s = "||")
    ]
  ; [ (* The Left shouldn't ever matter in practice. Should never get in a
         situation with two consecutive infix ? - the colon saves us. *)
      (TokenPrecedence, fun s -> Left, s = "?")
    ]
  ; [ (TokenPrecedence, fun s -> Right, s = ":=") ]
  ; [ (TokenPrecedence, fun s -> Right, s = updateToken) ]
  ; (* It's important to account for ternary ":" being lower precedence than
       "?" *)
    [ (TokenPrecedence, fun s -> Right, s = ":") ]
  ; [ (TokenPrecedence, fun s -> Nonassoc, s = "=>") ]
  ]

(* remove all prefixing backslashes, e.g. \=== becomes === *)
let without_prefixed_backslashes str =
  if str = ""
  then str
  else if String.get str 0 = '\\'
  then String.sub str 1 (String.length str - 1)
  else str

let indexOfFirstMatch ~prec lst =
  let rec aux n = function
    | [] -> None
    | [] :: tl -> aux (n + 1) tl
    | ((kind, tester) :: hdTl) :: tl ->
      (match prec, kind with
      | Token str, TokenPrecedence | Custom str, CustomPrecedence ->
        let associativity, foundMatch = tester str in
        if foundMatch then Some (associativity, n) else aux n (hdTl :: tl)
      | _ -> aux n (hdTl :: tl))
  in
  aux 0 lst

(* Assuming it's an infix function application. *)
let precedenceInfo ~prec =
  (* Removes prefixed backslashes in order to do proper conversion *)
  let prec =
    match prec with
    | Token str -> Token (without_prefixed_backslashes str)
    | Custom _ -> prec
  in
  indexOfFirstMatch ~prec rules

let isLeftAssociative ~prec =
  match precedenceInfo ~prec with
  | None -> false
  | Some (Left, _) -> true
  | Some (Right, _) -> false
  | Some (Nonassoc, _) -> false

let isRightAssociative ~prec =
  match precedenceInfo ~prec with
  | None -> false
  | Some (Right, _) -> true
  | Some (Left, _) -> false
  | Some (Nonassoc, _) -> false

let higherPrecedenceThan c1 c2 =
  match precedenceInfo ~prec:c1, precedenceInfo ~prec:c2 with
  | _, None | None, _ ->
    let str1, str2 =
      match c1, c2 with
      | Token s1, Token s2 -> "Token " ^ s1, "Token " ^ s2
      | Token s1, Custom s2 -> "Token " ^ s1, "Custom " ^ s2
      | Custom s1, Token s2 -> "Custom " ^ s1, "Token " ^ s2
      | Custom s1, Custom s2 -> "Custom " ^ s1, "Custom " ^ s2
    in
    raise
      (NotPossible
         ("Cannot determine precedence of two checks " ^ str1 ^ " vs. " ^ str2))
  | Some (_, p1), Some (_, p2) -> p1 < p2

let printedStringAndFixityExpr = function
  | { pexp_desc = Pexp_ident { txt = Lident l; _ }; _ } ->
    printedStringAndFixity l
  | _ -> Normal

(* which identifiers are in fact operators needing parentheses *)
let needs_parens txt =
  match printedStringAndFixity txt with
  | Infix _ -> true
  | UnaryPostfix _ -> true
  | UnaryPlusPrefix _ -> true
  | UnaryMinusPrefix _ -> true
  | UnaryNotPrefix _ -> true
  | AlmostSimplePrefix _ -> true
  | Letop _ -> true
  | Andop _ -> true
  | Normal -> false

(* some infixes need spaces around parens to avoid clashes with comment syntax.
   This isn't needed for comment syntax /* */ *)
let needs_spaces txt = txt.[0] = '*' || txt.[String.length txt - 1] = '*'

let rec orList = function
  (* only consider ((A|B)|C)*)
  | { ppat_desc = Ppat_or (p1, p2); _ } -> orList p1 @ orList p2
  | x -> [ x ]

(* variance encoding: need to sync up with the [parser.mly] *)
let type_variance = function
  | NoVariance -> ""
  | Covariant -> "+"
  | Contravariant -> "-"

let moduleIdent ident = match ident.txt with None -> "_" | Some name -> name

type construct =
  [ `cons of expression list
  | `list of expression list
  | `nil
  | `normal
  | `simple of Longident.t
  | `tuple
  ]

let view_expr x =
  match x.pexp_desc with
  | Pexp_construct ({ txt = Lident "()"; _ }, _) -> `tuple
  | Pexp_construct ({ txt = Lident "[]"; _ }, _) -> `nil
  | Pexp_construct ({ txt = Lident "::"; _ }, Some _) ->
    let rec loop exp acc =
      match exp with
      | { pexp_desc = Pexp_construct ({ txt = Lident "[]"; _ }, _); _ } ->
        List.rev acc, true
      | { pexp_desc =
            Pexp_construct
              ( { txt = Lident "::"; _ }
              , Some { pexp_desc = Pexp_tuple [ e1; e2 ]; _ } )
        ; _
        } ->
        loop e2 (e1 :: acc)
      | e -> List.rev (e :: acc), false
    in
    let ls, b = loop x [] in
    if b then `list ls else `cons ls
  | Pexp_construct (x, None) -> `simple x.txt
  | _ -> `normal

let is_simple_list_expr x =
  match view_expr x with `list _ | `cons _ -> true | _ -> false

let is_simple_construct : construct -> bool = function
  | `nil | `tuple | `list _ | `simple _ | `cons _ -> true
  | `normal -> false

let uncurriedTable = Hashtbl.create 42

(* Determines if a list of expressions contains a single unit construct
 * e.g. used to check: MyConstructor() -> exprList == [()]
 * useful to determine if MyConstructor(()) should be printed as MyConstructor()
 * *)
let is_single_unit_construct exprList =
  match exprList with
  | x :: [] ->
    let view = view_expr x in
    (match view with `tuple -> true | _ -> false)
  | _ -> false

let detectTernary l =
  match l with
  | [ { pc_lhs =
          { ppat_desc = Ppat_construct ({ txt = Lident "true"; _ }, _); _ }
      ; pc_guard = None
      ; pc_rhs = ifTrue
      }
    ; { pc_lhs =
          { ppat_desc = Ppat_construct ({ txt = Lident "false"; _ }, _); _ }
      ; pc_guard = None
      ; pc_rhs = ifFalse
      }
    ] ->
    Some (ifTrue, ifFalse)
  | _ -> None

type funcApplicationLabelStyle =
  (* No attaching to the label, but if the entire application fits on one line,
     the entire application will appear next to the label as you 'd expect. *)
  | NeverWrapFinalItem
  (* Attach the first term if there are exactly two terms involved in the
     application.

     let x = firstTerm (secondTerm_1 secondTerm_2) thirdTerm;

     Ideally, we'd be able to attach all but the last argument into the label
     any time all but the last term will fit - and *not* when (attaching all but
     the last term isn't enough to prevent a wrap) - But there's no way to tell
     ahead of time if it would prevent a wrap.

     However, the number two is somewhat convenient. This models the indentation
     that you'd prefer in non-curried syntax languages like JavaScript, where
     application only ever has two terms. *)
  | WrapFinalListyItemIfFewerThan of int

type formatSettings =
  { space : int
  ; (* For curried arguments in function *definitions* only: Number of [space]s
       to offset beyond the [let] keyword. Default 1. *)
    listsRecordsIndent : int
  ; indentWrappedPatternArgs : int
  ; (* Amount to indent in label-like constructs such as wrapped function
       applications, etc - or even record fields. This is not the same concept
       as an indented curried argument list. *)
    indentAfterLabels : int
  ; (* Amount to indent after the opening brace of switch/try.
     * Here's an example of what it would look like w/ [trySwitchIndent = 2]:
     * Sticks the expression to the last item in a sequence in several [X | Y | Z
     * => expr], and forces X, Y, Z to be split onto several lines. (Otherwise,
     * sticking to Z would result in hanging expressions).  TODO: In the first case,
     * it's clear that we want patterns to have an "extra" indentation with matching
     * in a "match". Create extra config param to pass to [self#pattern] for extra
     * indentation in this one case.
     *
     *  switch x {
     *  | TwoCombos
     *      (HeresTwoConstructorArguments x y)
     *      (HeresTwoConstructorArguments a b) =>
     *      ((a + b) + x) + y;
     *  | Short
     *  | AlsoHasARecord a b {x, y} => (
     *      retOne,
     *      retTwo
     *    )
     *  | AlsoHasARecord a b {x, y} =>
     *    callMyFunction
     *      withArg
     *      withArg
     *      withArg
     *      withArg;
     *  }
    *)
    trySwitchIndent : int
  ; (* In the case of two term function application (when flattened), the first
     * term should become part of the label, and the second term should be able to wrap
     * This doesn't effect n != 2.
     *
     *   [true]
     *   let x = reallyShort allFitsOnOneLine;
     *   let x = someFunction {
     *     reallyLongObject: true,
     *     thatWouldntFitOnThe: true,
     *     firstLine: true
     *   };
     *
     *   [false]
     *   let x = reallyShort allFitsOnOneLine;
     *   let x =
     *    someFunction
     *      {
     *        reallyLongObject: true,
     *        thatWouldntFitOnThe: true,
     *        firstLine: true
     *      };
    *)
    funcApplicationLabelStyle : funcApplicationLabelStyle
  ; funcCurriedPatternStyle : funcApplicationLabelStyle
  ; width : int
  ; assumeExplicitArity : bool
  ; constructorLists : string list
  }

let defaultSettings =
  { space = 1
  ; listsRecordsIndent = 2
  ; indentWrappedPatternArgs = 2
  ; indentAfterLabels = 2
  ; trySwitchIndent = 0
  ; funcApplicationLabelStyle = WrapFinalListyItemIfFewerThan 3
  ; (* WrapFinalListyItemIfFewerThan is currently a bad idea for curried
     * arguments: It looks great in some cases:
     *
     *    let myFun (a:int) :(
     *      int,
     *      string
     *    ) => (a, "this is a");
     *
     * But horrible in others:
     *
     *    let myFun
     *        {
     *          myField,
     *          yourField
     *        } :someReturnType => myField + yourField;
     *
     *    let myFun
     *        {            // Curried arg wraps
     *          myField,
     *          yourField
     *        } : (       // But the last is "listy" so it docks
     *      int,          // To the [let].
     *      int,
     *      int
     *    ) => myField + yourField;
     *
     * We probably want some special listy label docking/wrapping mode for
     * curried function bindings.
     *
    *)
    funcCurriedPatternStyle = NeverWrapFinalItem
  ; width = 80
  ; assumeExplicitArity = false
  ; constructorLists = []
  }

let configuredSettings = ref defaultSettings

let configure ~width ~assumeExplicitArity ~constructorLists =
  configuredSettings :=
    { defaultSettings with width; assumeExplicitArity; constructorLists }

let createFormatter () =
  let module Formatter = struct
    let settings = !configuredSettings

    (* How do we make
     * this a label?
     *
     * /---------------------\
     * let myVal = (oneThing, {
     * field: [],
     * anotherField: blah
     * });
     *
     * But in this case, this wider region a label?
     * /------------------------------------------------------\
     * let myVal = callSomeFunc (oneThing, {field: [], anotherField: blah}, {
     * boo: 'hi'
     * });
     *
     * This is difficult. You must form a label from the preorder traversal of every
     * node - except the last encountered in the traversal. An easier heuristic is:
     *
     * - The last argument to a functor application is expanded.
     *
     * React.CreateClass SomeThing {
     * let render {props} => {
     * };
     * }
     *
     * - The last argument to a function application is expanded on the same line.
     * - Only if it's not curried with another invocation.
     * -- Optionally: "only if everything else is an atom"
     * -- Optionally: "only if there are no other args"
     *
     * React.createClass someThing {
     * render: fn x => y,
     * }
     *
     * !!! NOT THIS
     * React.createClass someThing {
     * render: fn x => y,
     * }
     * somethingElse
    *)

    let isArityClear attrs =
      !configuredSettings.assumeExplicitArity
      || List.exists
           (function
             | { attr_name = { txt = "explicit_arity"; _ }; _ } -> true
             | _ -> false)
           attrs

    let default_indent_body = settings.listsRecordsIndent * settings.space

    let makeList
          ?listConfigIfCommentsInterleaved
          ?listConfigIfEolCommentsInterleaved
          ?(break = Layout.Never)
          ?(wrap = "", "")
          ?(inline = true, false)
          ?(sep = Layout.NoSep)
          ?(indent = default_indent_body)
          ?(sepLeft = true)
          ?(preSpace = false)
          ?(postSpace = false)
          ?(pad = false, false)
          lst
      =
      let config =
        { Layout.listConfigIfCommentsInterleaved
        ; listConfigIfEolCommentsInterleaved
        ; break = (if lst = [] then Layout.IfNeed else break)
        ; wrap
        ; inline
        ; sep
        ; indent
        ; sepLeft
        ; preSpace
        ; postSpace
        ; pad
        }
      in
      Layout.Sequence (config, lst)

    let makeAppList = function
      | [ hd ] -> hd
      | l -> makeList ~inline:(true, true) ~postSpace:true ~break:IfNeed l

    let makeTup ?(wrap = "", "") ?(trailComma = true) ?(uncurried = false) l =
      let lwrap, rwrap = wrap in
      let lparen = lwrap ^ if uncurried then "(. " else "(" in
      makeList
        ~wrap:(lparen, ")" ^ rwrap)
        ~sep:(if trailComma then commaTrail else commaSep)
        ~postSpace:true
        ~break:IfNeed
        l

    let ensureSingleTokenSticksToLabel x =
      let listConfigIfCommentsInterleaved cfg =
        let inline = true, true
        and postSpace = true
        and indent = 0 in
        { cfg with Layout.break = Always_rec; postSpace; indent; inline }
      in
      makeList ~listConfigIfCommentsInterleaved [ x ]

    let unbreakLabelFormatter formatter =
      let newFormatter labelTerm term =
        match formatter labelTerm term with
        | Easy_format.Label ((labelTerm, settings), term) ->
          Easy_format.Label
            ((labelTerm, { settings with label_break = `Never }), term)
        | _ -> failwith "not a label"
      in
      newFormatter

    let inlineLabel labelTerm term =
      let settings =
        { label_break = `Never
        ; space_after_label = true
        ; indent_after_label = 0
        ; label_style = Some "inlineLabel"
        }
      in
      Easy_format.Label ((labelTerm, settings), term)

    (* Just for debugging: Set debugWithHtml = true *)
    let debugWithHtml = ref false

    let html_escape_string s =
      let buf = Buffer.create (2 * String.length s) in
      for i = 0 to String.length s - 1 do
        match s.[i] with
        | '&' -> Buffer.add_string buf "&amp;"
        | '<' -> Buffer.add_string buf "&lt;"
        | '>' -> Buffer.add_string buf "&gt;"
        | c -> Buffer.add_char buf c
      done;
      Buffer.contents buf

    let html_escape = `Escape_string html_escape_string

    let html_style =
      [ "atom", { Easy_format.tag_open = "<a>"; tag_close = "</a>" }
      ; "body", { tag_open = "<lb>"; tag_close = "</lb>" }
      ; "list", { tag_open = "<l>"; tag_close = "</l>" }
      ; "op", { tag_open = "<op>"; tag_close = "</op>" }
      ; "cl", { tag_open = "<cl>"; tag_close = "</cl>" }
      ; "sep", { tag_open = "<sep>"; tag_close = "</sep>" }
      ; "label", { tag_open = "<la>"; tag_close = "</la>" }
      ]

    let easyLabel
          ?(break = `Auto)
          ?(space = false)
          ?(indent = settings.indentAfterLabels)
          labelTerm
          term
      =
      let settings =
        { label_break = break
        ; space_after_label = space
        ; indent_after_label = indent
        ; label_style = Some "label"
        }
      in
      Easy_format.Label ((labelTerm, settings), term)

    let label ?break ?space ?indent (labelTerm : Layout.t) (term : Layout.t) =
      Layout.Label (easyLabel ?break ?indent ?space, labelTerm, term)

    let atom ?loc str =
      let style = { Easy_format.atom_style = Some "atomClss" } in
      source_map ?loc (Layout.Easy (Easy_format.Atom (str, style)))

    (** Take x,y,z and n and generate [x, y, z, ...n] *)
    let makeES6List ?wrap:(lwrap, rwrap = "", "") lst last =
      makeList
        ~wrap:(lwrap ^ "[", "]" ^ rwrap)
        ~break:IfNeed
        ~postSpace:true
        ~sep:commaTrail
        (lst @ [ makeList [ atom "..."; last ] ])

    let makeNonIndentedBreakingList lst =
      (* No align closing: So that semis stick to the ends of every break *)
      makeList ~break:Always_rec ~indent:0 ~inline:(true, true) lst

    (* Like a <span> could place with other breakableInline lists without
       upsetting final semicolons *)
    let makeSpacedBreakableInlineList lst =
      makeList ~break:IfNeed ~inline:(true, true) ~postSpace:true lst

    let makeCommaBreakableListSurround opn cls lst =
      makeList ~break:IfNeed ~postSpace:true ~sep:(Sep ",") ~wrap:(opn, cls) lst

    (* TODO: Allow configuration of spacing around colon symbol *)

    let formatPrecedence ?(inline = false) ?(wrap = "(", ")") ?loc formattedTerm
      =
      source_map
        ?loc
        (makeList ~inline:(true, inline) ~wrap ~break:IfNeed [ formattedTerm ])

    let wrap fn term =
      ignore (Format.flush_str_formatter ());
      fn Format.str_formatter term;
      atom (Format.flush_str_formatter ())

    let quoted_ext ?(pct = "%") extension i delim =
      wrap
        (fun ppf () ->
           Format.fprintf
             ppf
             "{%s%s%s%s|%s|%s}"
             pct
             extension.txt
             (if delim != "" then " " else "")
             delim
             i
             delim)
        ()

    (* Don't use `trim` since it kills line return too? *)
    let rec beginsWithStar_ line length idx =
      if idx = length
      then false
      else
        match String.get line idx with
        | '*' -> true
        | '\t' | ' ' -> beginsWithStar_ line length (idx + 1)
        | _ -> false

    let beginsWithStar line = beginsWithStar_ line (String.length line) 0

    let rec numLeadingSpace_ line length idx accum =
      if idx = length
      then accum
      else
        match String.get line idx with
        | '\t' | ' ' -> numLeadingSpace_ line length (idx + 1) (accum + 1)
        | _ -> accum

    let numLeadingSpace line = numLeadingSpace_ line (String.length line) 0 0

    (* Computes the smallest leading spaces for non-empty lines *)
    let smallestLeadingSpaces strs =
      let rec smallestLeadingSpaces curMin strs =
        match strs with
        | [] -> curMin
        | "" :: tl -> smallestLeadingSpaces curMin tl
        | hd :: tl ->
          let leadingSpace = numLeadingSpace hd in
          let nextMin = min curMin leadingSpace in
          smallestLeadingSpaces nextMin tl
      in
      smallestLeadingSpaces 99999 strs

    let rec isSequencey = function
      | Layout.SourceMap (_, sub) -> isSequencey sub
      | Layout.Sequence _ -> true
      | Layout.Label (_, _, _) -> false
      | Layout.Easy (Easy_format.List _) -> true
      | Layout.Easy _ -> false
      | Layout.Whitespace (_, sub) -> isSequencey sub

    let inline ?(preSpace = false) ?(postSpace = false) labelTerm term =
      makeList
        [ labelTerm; term ]
        ~inline:(true, true)
        ~postSpace
        ~preSpace
        ~indent:0
        ~break:Layout.Never

    let breakline labelTerm term =
      makeList
        [ labelTerm; term ]
        ~inline:(true, true)
        ~indent:0
        ~break:Always_rec

    let insertBlankLines n term =
      if n = 0
      then term
      else
        makeList
          ~inline:(true, true)
          ~indent:0
          ~break:Always_rec
          (Array.to_list (Array.make n (atom "")) @ [ term ])

    let string_after s n = String.sub s n (String.length s - n)

    (* This is a special-purpose functions only used by `formatComment_`. Notice
       we skip a char below during usage because we know the comment starts with
       `/*` *)
    let rec lineZeroMeaningfulContent_ line length idx accum =
      if idx = length
      then None
      else
        let ch = String.get line idx in
        if ch = '\t' || ch = ' ' || ch = '*'
        then lineZeroMeaningfulContent_ line length (idx + 1) (accum + 1)
        else Some accum

    let lineZeroMeaningfulContent line =
      lineZeroMeaningfulContent_ line (String.length line) 1 0

    let formatComment_ txt =
      let commLines =
        Reason_syntax_util.split_by
          ~keep_empty:true
          (fun x -> x = '\n')
          (Comment.wrap txt)
      in
      match commLines with
      | [] -> atom ""
      | [ hd ] -> atom hd
      | zero :: one :: tl ->
        let attemptRemoveCount = smallestLeadingSpaces (one :: tl) in
        let leftPad =
          if beginsWithStar one
          then 1
          else
            match lineZeroMeaningfulContent zero with
            | None -> 1
            | Some num -> num + 1
        in
        let padNonOpeningLine s =
          let numLeadingSpaceForThisLine = numLeadingSpace s in
          if String.length s == 0
          then ""
          else
            String.make leftPad ' '
            ^ string_after s (min attemptRemoveCount numLeadingSpaceForThisLine)
        in
        let lines = zero :: List.map padNonOpeningLine (one :: tl) in
        makeList
          ~inline:(true, true)
          ~indent:0
          ~break:Always_rec
          (List.map atom lines)

    let formatComment comment =
      source_map ~loc:(Comment.location comment) (formatComment_ comment)

    let[@tail_mod_cons] rec append ?(space = false) txt = function
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, append ~space txt sub)
      | Sequence (config, l) when snd config.wrap <> "" ->
        let sep = if space then " " else "" in
        Sequence
          ( { config with wrap = fst config.wrap, snd config.wrap ^ sep ^ txt }
          , l )
      | Sequence (config, []) -> Sequence (config, [ atom txt ])
      | Sequence (({ sep = NoSep; _ } as config), l)
      | Sequence (({ sep = Sep ""; _ } as config), l) ->
        let sub = appendSub txt ~space l in
        Sequence (config, sub)
      | Label (formatter, left, right) ->
        Label (formatter, left, append ~space txt right)
      | Whitespace (info, sub) -> Whitespace (info, append ~space txt sub)
      | layout -> (inline [@tailcall false]) ~postSpace:space layout (atom txt)

    and[@tail_mod_cons] appendSub txt ~space layouts =
      match layouts with
      | [] -> []
      | [ layout ] -> [ append ~space txt layout ]
      | layout :: xs -> layout :: appendSub txt ~space xs

    let appendSep spaceBeforeSep sep layout =
      append (if spaceBeforeSep then " " ^ sep else sep) layout

    let rec flattenCommentAndSep ?(spaceBeforeSep = false) ?sepStr = function
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, flattenCommentAndSep ~spaceBeforeSep ?sepStr sub)
      | Layout.Whitespace (info, sub) ->
        Layout.Whitespace
          (info, flattenCommentAndSep ~spaceBeforeSep ?sepStr sub)
      | layout ->
        (match sepStr with
        | None -> layout
        | Some sep -> appendSep spaceBeforeSep sep layout)

    let rec preOrderWalk f layout =
      match f layout with
      | Layout.Sequence (listConfig, sublayouts) ->
        let newSublayouts = List.map (preOrderWalk f) sublayouts in
        Layout.Sequence (listConfig, newSublayouts)
      | Layout.Label (formatter, left, right) ->
        let newLeftLayout = preOrderWalk f left in
        let newRightLayout = preOrderWalk f right in
        Layout.Label (formatter, newLeftLayout, newRightLayout)
      | Layout.SourceMap (loc, sub) -> Layout.SourceMap (loc, preOrderWalk f sub)
      | Layout.Easy _ as layout -> layout
      | Layout.Whitespace (info, sub) ->
        Layout.Whitespace (info, preOrderWalk f sub)

    (** Recursively unbreaks a layout to make sure they stay within the same
        line *)
    let unbreaklayout =
      preOrderWalk (function
        | Layout.Sequence (listConfig, sublayouts) ->
          Layout.Sequence ({ listConfig with break = Layout.Never }, sublayouts)
        | Layout.Label (formatter, left, right) ->
          Layout.Label (unbreakLabelFormatter formatter, left, right)
        | layout -> layout)

    (** [consolidateSeparator layout] walks the [layout], extract separators out
        of each * list and insert them into PrintTree as separated items *)
    let consolidateSeparator l =
      preOrderWalk
        (function
          | Sequence (listConfig, sublayouts)
            when listConfig.sep != NoSep && listConfig.sepLeft ->
            (* TODO: Support !sepLeft, and this should apply to the *first*
                separator if !sepLeft. *)
            let[@tail_mod_cons] rec mapSublayout layouts =
              match listConfig.sep, layouts with
              | NoSep, _ ->
                raise
                  (NotPossible
                     "We already covered this case. This shouldn't happen.")
              | Sep _, [ layout ] -> [ layout ]
              | (SepFinal (sepStr, _) | Sep sepStr), layout :: l2 :: xs ->
                flattenCommentAndSep
                  ~spaceBeforeSep:listConfig.preSpace
                  ~sepStr
                  layout
                :: mapSublayout (l2 :: xs)
              | SepFinal (_, finalSepStr), [ layout ] ->
                [ flattenCommentAndSep
                    ~spaceBeforeSep:listConfig.preSpace
                    ~sepStr:finalSepStr
                    layout
                ]
              | _, [] -> []
            in
            let layoutsWithSepAndComment = mapSublayout sublayouts in
            let sep = Layout.NoSep in
            let preSpace = false in
            Sequence
              ({ listConfig with sep; preSpace }, layoutsWithSepAndComment)
          | layout -> layout)
        l

    (** [insertLinesAboveItems layout] walks the [layout] and insert empty lines *)
    let insertLinesAboveItems items =
      preOrderWalk
        (function
          | Whitespace (region, sub) ->
            insertBlankLines (WhitespaceRegion.newlines region) sub
          | layout -> layout)
        items

    let insertCommentIntoWhitespaceRegion comment region subLayout =
      let cl = Comment.location comment in
      let range = WhitespaceRegion.range region in
      (* append the comment to the list of inserted comments in the whitespace
         region *)
      let nextRegion = WhitespaceRegion.addComment region comment in
      let formattedComment = formatComment comment in
      match WhitespaceRegion.comments region with
      (* the comment inserted into the whitespace region is the first in the
         region *)
      | [] ->
        (* 1| let a = 1;
         * 2|
         * 3| /* comment at end of whitespace region */
         * 4| let b = 2;
        *)
        if range.lnum_end = cl.loc_end.pos_lnum
        then
          let subLayout = breakline formattedComment subLayout in
          Layout.Whitespace (nextRegion, subLayout)
          (* 1| let a = 1;
           * 2| /* comment at start of whitespace region */
           * 3|
           * 4| let b = 2;
          *)
        else if range.lnum_start = cl.loc_start.pos_lnum
        then
          let subLayout =
            breakline formattedComment (insertBlankLines 1 subLayout)
          in
          let nextRegion = WhitespaceRegion.modifyNewlines nextRegion 0 in
          Whitespace (nextRegion, subLayout)
          (* 1| let a = 1;
           * 2|
           * 3| /* comment floats in whitespace region */
           * 4|
           * 5| let b = 2;
          *)
        else
          let subLayout =
            breakline formattedComment (insertBlankLines 1 subLayout)
          in
          Whitespace (nextRegion, subLayout)
      (* The whitespace region contains already inserted comments *)
      | prevComment :: _cs ->
        let pcl = Comment.location prevComment in
        (* check if the comment is attached to the start of the region *)
        let attachedToStartRegion = cl.loc_start.pos_lnum = range.lnum_start in
        let nextRegion =
          (* 1| let a = 1;
           * 2| /* comment sits on the beginning of the region */
           * 3| /* previous comment */
           * 4|
           * 5| let b = 2;
          *)
          if attachedToStartRegion
          then
            (* we don't want a newline between `let a = 1` and the `comment sits
             * on the beginning of the region` comment*)
            WhitespaceRegion.modifyNewlines nextRegion 0
            (* 1| let a = 1;
             * 2|
             * 3| /* comment isn't located at the beginnin of a region*/
             * 4| /* previous comment */
             * 5|
             * 6| let b = 2;
            *)
          else nextRegion
        in
        (* 1| let a = 1;
         * 2| /* comment */
         * 3|                      --> whitespace between
         * 4| /* previous comment */
         * 5| let b = 1;
        *)
        if Reason_location.hasSpaceBetween pcl cl
        then
          (* pcl.loc_start.pos_lnum - cl.loc_end.pos_lnum > 1 then *)
          let subLayout =
            breakline formattedComment (insertBlankLines 1 subLayout)
          in
          let withComment = Layout.Whitespace (nextRegion, subLayout) in
          withComment
          (* 1| let a = 1;
           * 2|
           * 3| /* comment */          | no whitespace between `comment`
           * 4| /* previous comment */ | and `previous comment`
           * 5| let b = 1;
          *)
        else
          let subLayout = breakline formattedComment subLayout in
          let withComment = Layout.Whitespace (nextRegion, subLayout) in
          withComment

    (** * prependSingleLineComment inserts a single line comment right above
        layout *)
    let rec prependSingleLineComment comment layout =
      match layout with
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, prependSingleLineComment comment sub)
      | Sequence (config, hd :: tl) when config.break = Always_rec ->
        Sequence (config, prependSingleLineComment comment hd :: tl)
      | Whitespace (info, sub) ->
        insertCommentIntoWhitespaceRegion comment info sub
      | layout -> breakline (formatComment comment) layout

    (* breakAncestors break ancestors above node, but not comment attachment
       itself.*)
    let appendComment ~breakAncestors layout comment =
      let text = Comment.wrap comment in
      let layout =
        match layout with
        | Layout.Whitespace (info, sublayout) ->
          Layout.Whitespace
            ( info
            , makeList
                ~break:Layout.Never
                ~postSpace:true
                [ sublayout; atom text ] )
        | layout ->
          makeList ~break:Layout.Never ~postSpace:true [ layout; atom text ]
      in
      if breakAncestors
      then
        makeList
          ~inline:(true, true)
          ~postSpace:false
          ~preSpace:true
          ~indent:0
          ~break:Always_rec
          [ layout ]
      else layout

    (** * [looselyAttachComment layout comment] preorderly walks the layout and
        * find a place where the comment can be loosely attached to *)
    let rec looselyAttachComment ~breakAncestors layout comment =
      let location = Comment.location comment in
      match layout with
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, looselyAttachComment ~breakAncestors sub comment)
      | Layout.Whitespace (info, sub) ->
        Layout.Whitespace
          (info, looselyAttachComment ~breakAncestors sub comment)
      | Easy _ -> inline ~postSpace:true layout (formatComment comment)
      | Sequence (listConfig, subLayouts)
        when List.exists (Layout.contains_location ~location) subLayouts ->
        (* If any of the subLayout strictly contains this comment, recurse into
           to it *)
        let recurse_sublayout layout =
          if Layout.contains_location layout ~location
          then looselyAttachComment ~breakAncestors layout comment
          else layout
        in
        Sequence (listConfig, List.map recurse_sublayout subLayouts)
      | Sequence (listConfig, subLayouts) when subLayouts == [] ->
        (* If there are no subLayouts (empty body), create a Sequence of just
           the comment *)
        Sequence (listConfig, [ formatComment comment ])
      | Sequence (listConfig, subLayouts) ->
        let beforeComment, afterComment =
          Reason_syntax_util.pick_while (Layout.is_before ~location) subLayouts
        in
        let newSubLayout =
          match List.rev beforeComment with
          | [] ->
            Reason_syntax_util.map_first
              (prependSingleLineComment comment)
              afterComment
          | hd :: tl ->
            List.rev_append
              (appendComment ~breakAncestors hd comment :: tl)
              afterComment
        in
        Sequence (listConfig, newSubLayout)
      | Label (formatter, left, right) ->
        let newLeft, newRight =
          match Layout.get_location left, Layout.get_location right with
          | None, None ->
            left, looselyAttachComment ~breakAncestors right comment
          | _, Some loc2 when Reason_syntax_util.location_contains loc2 location
            ->
            left, looselyAttachComment ~breakAncestors right comment
          | Some loc1, _ when Reason_syntax_util.location_contains loc1 location
            ->
            looselyAttachComment ~breakAncestors left comment, right
          | Some loc1, Some _
            when Reason_syntax_util.location_is_before location loc1 ->
            prependSingleLineComment comment left, right
          | Some _, Some loc2
            when Reason_syntax_util.location_is_before location loc2 ->
            left, prependSingleLineComment comment right
          | _ -> left, appendComment ~breakAncestors right comment
        in
        Label (formatter, newLeft, newRight)

    (** * [insertSingleLineComment layout comment] preorderly walks the layout
        and * find a place where the SingleLineComment can be fit into *)
    let rec insertSingleLineComment layout comment =
      let location = Comment.location comment in
      match layout with
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, insertSingleLineComment sub comment)
      | Layout.Whitespace (info, sub) ->
        let range = WhitespaceRegion.range info in
        if Range.containsLoc range location
        then insertCommentIntoWhitespaceRegion comment info sub
        else Layout.Whitespace (info, insertSingleLineComment sub comment)
      | Easy _ -> prependSingleLineComment comment layout
      | Sequence (listConfig, subLayouts) when subLayouts == [] ->
        (* If there are no subLayouts (empty body), create a Sequence of just the
         * comment. We need to be careful when the empty body contains a //-style
         * comment. Example:
         *   let make = () => {
         *     //
         *   };
         * It is clear that the sequence needs to always break here, otherwise
         * we get a parse error: let make = () => { // };
         * The closing brace and semicolon `};` would become part of the comment…
        *)
        let listConfig =
          if Reason_comment.isLineComment comment
          then { listConfig with break = Always_rec }
          else listConfig
        in
        Sequence (listConfig, [ formatComment comment ])
      | Sequence (listConfig, subLayouts) ->
        let beforeComment, afterComment =
          Reason_syntax_util.pick_while (Layout.is_before ~location) subLayouts
        in
        (match afterComment with
        (* Nothing in the list is after comment, attach comment to the statement
           before the comment *)
        | [] ->
          let break sublayout = breakline sublayout (formatComment comment) in
          Sequence (listConfig, Reason_syntax_util.map_last break beforeComment)
        | hd :: tl ->
          let afterComment =
            match Layout.get_location hd with
            | Some loc when Reason_syntax_util.location_contains loc location ->
              insertSingleLineComment hd comment :: tl
            | Some loc ->
              Layout.SourceMap (loc, prependSingleLineComment comment hd) :: tl
            | _ -> prependSingleLineComment comment hd :: tl
          in
          Sequence (listConfig, beforeComment @ afterComment))
      | Label (formatter, left, right) ->
        let leftLoc = Layout.get_location left in
        let rightLoc = Layout.get_location right in
        let newLeft, newRight =
          match leftLoc, rightLoc with
          | None, None -> left, insertSingleLineComment right comment
          | _, Some loc2 when Reason_syntax_util.location_contains loc2 location
            ->
            left, insertSingleLineComment right comment
          | Some loc1, _ when Reason_syntax_util.location_contains loc1 location
            ->
            insertSingleLineComment left comment, right
          | Some loc1, Some _
            when Reason_syntax_util.location_is_before location loc1 ->
            prependSingleLineComment comment left, right
          | Some _, Some loc2
            when Reason_syntax_util.location_is_before location loc2 ->
            left, prependSingleLineComment comment right
          | _ -> left, breakline right (formatComment comment)
        in
        Label (formatter, newLeft, newRight)

    let rec attachCommentToNodeRight layout comment =
      match layout with
      | Layout.Sequence (config, sub) when snd config.wrap <> "" ->
        (* jwalke: This is quite the abuse of the "wrap" config *)
        let lwrap, rwrap = config.wrap in
        let rwrap = rwrap ^ " " ^ Comment.wrap comment in
        Layout.Sequence ({ config with wrap = lwrap, rwrap }, sub)
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, attachCommentToNodeRight sub comment)
      | layout -> inline ~postSpace:true layout (formatComment comment)

    let rec attachCommentToNodeLeft comment layout =
      match layout with
      | Layout.Sequence (config, sub) when snd config.wrap <> "" ->
        let lwrap, rwrap = config.wrap in
        let lwrap = Comment.wrap comment ^ " " ^ lwrap in
        Layout.Sequence ({ config with wrap = lwrap, rwrap }, sub)
      | Layout.SourceMap (loc, sub) ->
        Layout.SourceMap (loc, attachCommentToNodeLeft comment sub)
      | layout -> Layout.Label (inlineLabel, formatComment comment, layout)

    (* [tryPerfectlyAttachComment layout comment] postorderly walk the [layout] and tries
     *  to perfectly attach a comment with a layout node.
     *
     *  Perfectly attach here means a comment's start location is equal to the node's end location
     *  and vice versa.
     *
     *  If the comment can be perfectly attached to any layout node, returns (newLayout, None),
     *  meaning the comment is consumed. Otherwise returns the (unchangedLayout, Some comment),
     *  meaning the comment is not consumed.
     *
     * "perfect attachment" doesn't make sense for end of line comments:
     *
     *       {
     *         x: 0,
     *         y: 0
     *       }
     *
     * One of these will be "perfectly attached" to the zero and the other won't.
     * Why should the comma have such an influence? Trailing commas and semicolons
     * may be inserted or removed, an we need end-of-line comments to never be
     * impacted by that. Therefore, never try to "perfectly" attach EOL comments.
    *)
    let rec tryPerfectlyAttachComment layout = function
      | None -> layout, None
      | Some comment -> perfectlyAttachComment comment layout

    and perfectlyAttachComment comment = function
      | Layout.Sequence (listConfig, subLayouts) ->
        let distributeCommentIntoSubLayouts (i, processed, newComment) layout =
          let layout, newComment =
            tryPerfectlyAttachComment layout newComment
          in
          i + 1, layout :: processed, newComment
        in
        let _, processed, consumed =
          List.fold_left
            distributeCommentIntoSubLayouts
            (0, [], Some comment)
            (List.rev subLayouts)
        in
        Layout.Sequence (listConfig, processed), consumed
      | Layout.Label (labelFormatter, left, right) ->
        let newRight, comment = perfectlyAttachComment comment right in
        let newLeft, comment = tryPerfectlyAttachComment left comment in
        Layout.Label (labelFormatter, newLeft, newRight), comment
      | Layout.SourceMap (loc, subLayout) ->
        let commloc = Comment.location comment in
        if
          loc.loc_end.Lexing.pos_lnum = loc.loc_start.Lexing.pos_lnum
          && commloc.loc_start.Lexing.pos_cnum = loc.loc_end.Lexing.pos_cnum
        then
          ( Layout.SourceMap
              ( loc
              , makeList
                  ~inline:(true, true)
                  ~break:Always
                  [ unbreaklayout (attachCommentToNodeRight subLayout comment) ]
              )
          , None )
        else
          let layout, comment = perfectlyAttachComment comment subLayout in
          (match comment with
          | None -> Layout.SourceMap (loc, layout), None
          | Some comment ->
            if commloc.loc_end.Lexing.pos_cnum = loc.loc_start.Lexing.pos_cnum
            then
              ( Layout.SourceMap (loc, attachCommentToNodeLeft comment layout)
              , None )
            else if
              commloc.loc_start.Lexing.pos_cnum = loc.loc_end.Lexing.pos_cnum
            then
              ( Layout.SourceMap (loc, attachCommentToNodeRight layout comment)
              , None )
            else Layout.SourceMap (loc, layout), Some comment)
      | Whitespace (info, subLayout) ->
        (match perfectlyAttachComment comment subLayout with
        | newLayout, None -> Whitespace (info, newLayout), None
        | newLayout, Some c -> Whitespace (info, newLayout), Some c)
      | layout -> layout, Some comment

    let insertRegularComment layout comment =
      match perfectlyAttachComment comment layout with
      | layout, None -> layout
      | layout, Some _ ->
        looselyAttachComment ~breakAncestors:false layout comment

    let insertEndOfLineComment layout comment =
      looselyAttachComment ~breakAncestors:true layout comment

    let rec partitionComments_ ((singleLines, endOfLines, regulars) as soFar)
      = function
      | [] -> soFar
      | com :: tl ->
        (match Comment.category com with
        | Comment.EndOfLine ->
          partitionComments_ (singleLines, com :: endOfLines, regulars) tl
        | Comment.SingleLine ->
          partitionComments_ (com :: singleLines, endOfLines, regulars) tl
        | Comment.Regular ->
          partitionComments_ (singleLines, endOfLines, com :: regulars) tl)

    let partitionComments comments =
      let singleLines, endOfLines, regulars =
        partitionComments_ ([], [], []) comments
      in
      singleLines, List.rev endOfLines, regulars

    (*
       * Partition single line comments based on a location into two lists:
     * - one contains the comments before/same height of that location
     * - the other contains the comments after the location
    *)
    let partitionSingleLineComments loc singleLineComments =
      let before, after =
        List.fold_left
          (fun (before, after) comment ->
             let cl = Comment.location comment in
             let isAfter = loc.loc_end.pos_lnum < cl.loc_start.pos_lnum in
             if isAfter
             then before, comment :: after
             else comment :: before, after)
          ([], [])
          singleLineComments
      in
      List.rev before, after

    (*
       * appends all [singleLineComments] after the [layout].
     * [loc] marks the end of [layout]
    *)
    let appendSingleLineCommentsToEnd loc layout singleLineComments =
      let rec aux prevLoc layout i = function
        | comment :: cs ->
          let loc = Comment.location comment in
          let formattedComment = formatComment comment in
          let commentLayout =
            if Reason_location.hasSpaceBetween loc prevLoc
            then insertBlankLines 1 formattedComment
            else formattedComment
          in
          (* The initial layout breaks ugly with `breakline`,
           * an inline list (that never breaks) fixes this *)
          let newLayout =
            if i == 0
            then
              makeList
                ~inline:(true, true)
                ~break:Never
                [ layout; commentLayout ]
            else breakline layout commentLayout
          in
          aux loc newLayout (i + 1) cs
        | [] -> layout
      in
      aux loc layout 0 singleLineComments

    (*
       * For simplicity, the formatting of comments happens in two parts in context of a source map:
     * 1) insert the singleLineComments with the interleaving algorithm contained in
     *    `insertSingleLineComment` for all comments overlapping with the sourcemap.
     *    A `Layout.Whitespace` node signals an intent to preserve whitespace here.
     * 2) SingleLineComments after the sourcemap, e.g. at the end of .re/.rei file,
     *    get attached with `appendSingleLineCommentsToEnd`. Due to the fact there
     *    aren't any real ocaml ast nodes anymore after the sourcemap (end of a
     *    file), the printing of the comments can be done in one pass with
     *    `appendSingleLineCommentsToEnd`. This is more performant and
     *    simplifies the implementation of comment attachment.
    *)
    let attachSingleLineComments singleLineComments = function
      | Layout.SourceMap (loc, subLayout) ->
        let before, after =
          partitionSingleLineComments loc singleLineComments
        in
        let layout = List.fold_left insertSingleLineComment subLayout before in
        appendSingleLineCommentsToEnd loc layout after
      | layout ->
        List.fold_left insertSingleLineComment layout singleLineComments

    let format_layout ?comments ppf layout =
      let easy =
        match comments with
        | None -> Layout.to_easy_format layout
        | Some comments ->
          let singleLines, endOfLines, regulars = partitionComments comments in
          (* TODO: Stop generating multiple versions of the tree, and instead
             generate one new tree. *)
          (* Layout.dump Format.std_formatter layout; *)
          let layout = List.fold_left insertRegularComment layout regulars in
          let layout = consolidateSeparator layout in
          let layout =
            List.fold_left insertEndOfLineComment layout endOfLines
          in
          (* Layout.dump Format.std_formatter layout; *)
          let layout = attachSingleLineComments singleLines layout in
          (* Layout.dump Format.std_formatter layout; *)
          let layout = insertLinesAboveItems layout in
          let layout = Layout.to_easy_format layout in
          (* Layout.dump_easy Format.std_formatter layout; *)
          layout
      in
      let buf = Buffer.create 1000 in
      let fauxmatter = Format.formatter_of_buffer buf in
      let _ = Format.pp_set_margin fauxmatter settings.width in
      if debugWithHtml.contents
      then Easy_format.Pretty.define_styles fauxmatter html_escape html_style;
      let _ = Easy_format.Pretty.to_formatter fauxmatter easy in
      let trimmed =
        Reason_syntax_util.processLineEndingsAndStarts (Buffer.contents buf)
      in
      Format.fprintf ppf "%s\n" trimmed;
      Format.pp_print_flush ppf ()

    let rev_and_len xs =
      let rec rev_and_len acc len xs =
        match xs with
        | [] -> acc, len
        | x :: xs -> rev_and_len (x :: acc) (len + 1) xs
      in
      rev_and_len [] 0 xs

    let partitionFinalWrapping listTester wrapFinalItemSetting x =
      let rev, len = rev_and_len x in
      match rev, wrapFinalItemSetting with
      | [], _ ->
        raise (NotPossible "shouldnt be partitioning 0 label attachments")
      | _, NeverWrapFinalItem -> None
      | last :: revEverythingButLast, WrapFinalListyItemIfFewerThan max ->
        if (not (listTester last)) || len >= max
        then None
        else Some (List.rev revEverythingButLast, last)

    let semiTerminated term = makeList [ term; atom ";" ]

    (* postSpace is so that when comments are interleaved, we still use spacing
       rules. *)
    let makeLetSequence ?(wrap = "{", "}") letItems =
      makeList
        ~break:Always_rec
        ~inline:(true, false)
        ~wrap
        ~postSpace:true
        ~sep:(SepFinal (";", ";"))
        letItems

    let makeLetSequenceSingleLine ?(wrap = "{", "}") letItems =
      makeList
        ~break:IfNeed
        ~inline:(true, false)
        ~wrap
        ~preSpace:true
        ~postSpace:true
        ~sep:(Sep ";")
        letItems

    (* postSpace is so that when comments are interleaved, we still use spacing
       rules. *)
    let makeUnguardedLetSequence ?(sep = Layout.SepFinal (";", ";")) letItems =
      makeList
        ~break:Always_rec
        ~inline:(true, true)
        ~wrap:("", "")
        ~indent:0
        ~postSpace:true
        ~sep
        letItems

    let formatSimpleAttributed x y =
      makeList
        ~wrap:("(", ")")
        ~break:IfNeed
        ~indent:0
        ~postSpace:true
        (List.concat [ y; [ x ] ])

    let formatAttributed ?(labelBreak = `Auto) x y =
      label
        ~break:labelBreak
        ~indent:0
        ~space:true
        (makeList ~inline:(true, true) ~postSpace:true y)
        x

    (* For when the type constraint should be treated as a separate breakable
       line item itself not docked to some value/pattern label. fun x y :
       retType => blah; *)
    let formatJustTheTypeConstraint typ =
      makeList ~postSpace:false ~sep:(Sep " ") [ atom ":"; typ ]

    let formatTypeConstraint one two =
      label ~space:true (makeList ~postSpace:false [ one; atom ":" ]) two

    let formatCoerce expr optType coerced =
      match optType with
      | None ->
        label ~space:true (makeList ~postSpace:true [ expr; atom ":>" ]) coerced
      | Some typ ->
        label
          ~space:true
          (makeList
             ~postSpace:true
             [ formatTypeConstraint expr typ; atom ":>" ])
          coerced

    (* Standard function application style indentation - no special wrapping
     * behavior.
     *
     * Formats like this:
     *
     *   let result =
     *     someFunc
     *       (10, 20);
     *
     *
     * Instead of this:
     *
     *   let result =
     *     someFunc (
     *       10,
     *       20
     *     );
     *
     * The outer list wrapping fixes #566: format should break the whole
     * application before breaking arguments.
    *)
    let formatIndentedApplication headApplicationItem argApplicationItems =
      makeList
        ~inline:(true, true)
        ~postSpace:true
        ~break:IfNeed
        [ label
            ~space:true
            headApplicationItem
            (makeAppList argApplicationItems)
        ]

    (* The loc, is an optional location or the returned app terms *)
    let formatAttachmentApplication
          finalWrapping
          (attachTo : (bool * Layout.t) option)
          (appTermItems, loc)
      =
      let partitioning = finalWrapping appTermItems in
      match partitioning with
      | None ->
        (match appTermItems, attachTo with
        | [], _ -> raise (NotPossible "No app terms")
        | [ hd ], None -> source_map ?loc hd
        | [ hd ], Some (useSpace, toThis) ->
          label ~space:useSpace toThis (source_map ?loc hd)
        | hd :: tl, None -> source_map ?loc (formatIndentedApplication hd tl)
        | hd :: tl, Some (useSpace, toThis) ->
          label
            ~space:useSpace
            toThis
            (source_map ?loc (formatIndentedApplication hd tl)))
      | Some (attachedList, wrappedListy) ->
        (match attachedList, attachTo with
        | [], Some (useSpace, toThis) ->
          label ~space:useSpace toThis (source_map ?loc wrappedListy)
        | [], None ->
          (* Not Sure when this would happen *)
          source_map ?loc wrappedListy
        | _ :: _, Some (useSpace, toThis) ->
          (* TODO: Can't attach location to this - maybe rewrite anyways *)
          let attachedArgs = makeAppList attachedList in
          label
            ~space:useSpace
            toThis
            (label ~space:true attachedArgs wrappedListy)
        | _ :: _, None ->
          (* Args that are "attached to nothing" *)
          let appList = makeAppList attachedList in
          source_map ?loc (label ~space:true appList wrappedListy))

    (* Preprocesses an expression term for the sake of label attachments ([letx
       = expr]or record [field: expr]). Function application should have special
       treatment when placed next to a label. (The invoked function term should
       "stick" to the label in some cases). In others, the invoked function term
       should become a new label for the remaining items to be indented
       under. *)
    let applicationFinalWrapping x =
      partitionFinalWrapping isSequencey settings.funcApplicationLabelStyle x

    let curriedFunctionFinalWrapping x =
      partitionFinalWrapping isSequencey settings.funcCurriedPatternStyle x

    let typeApplicationFinalWrapping typeApplicationItems =
      partitionFinalWrapping
        isSequencey
        settings.funcApplicationLabelStyle
        typeApplicationItems

    (* add parentheses to binders when they are in fact infix or prefix
       operators *)
    let protectIdentifier txt =
      let needs_parens = needs_parens txt in
      let txt =
        if Reason_syntax_util.is_andop txt || Reason_syntax_util.is_letop txt
        then Reason_syntax_util.compress_letop_identifier txt
        else txt
      in
      if not needs_parens
      then atom txt
      else if needs_spaces txt
      then makeList ~wrap:("(", ")") ~pad:(true, true) [ atom txt ]
      else atom ("(" ^ txt ^ ")")

    let protectLongIdentifier longPrefix txt =
      makeList [ longPrefix; atom "."; protectIdentifier txt ]

    let paren b fu ppf x =
      if b then Format.fprintf ppf "(%a)" fu x else fu ppf x

    let constant_string_for_primitive ppf s =
      let hasQuote = try String.index s '"' with Not_found -> -1 in
      let hasNewline = try String.index s '\n' with Not_found -> -1 in
      if hasQuote > -1 || hasNewline > -1
      then Format.fprintf ppf "{|%s|}" s
      else Format.fprintf ppf "%S" s

    let tyvar ppf str = Format.fprintf ppf "'%s" str

    (* In some places parens shouldn't be printed for readability:
     * e.g. Some((-1)) should be printed as Some(-1)
     * In `1 + (-1)` -1 should be wrapped in parens for readability
    *)
    let constant ?raw_literal ?(parens = true) ppf = function
      | Pconst_char i -> Format.fprintf ppf "%C" i
      | Pconst_string (i, _, None) ->
        (match raw_literal with
        | Some text -> Format.fprintf ppf "\"%s\"" text
        | None ->
          Format.fprintf ppf "\"%s\"" (Reason_syntax_util.escape_string i))
      | Pconst_string (i, _, Some delim) ->
        Format.fprintf ppf "{%s|%s|%s}" delim i delim
      | Pconst_integer (i, None) ->
        paren (parens && i.[0] = '-') (fun ppf -> Format.fprintf ppf "%s") ppf i
      | Pconst_integer (i, Some m) ->
        paren
          (parens && i.[0] = '-')
          (fun ppf (i, m) -> Format.fprintf ppf "%s%c" i m)
          ppf
          (i, m)
      | Pconst_float (i, None) ->
        paren (parens && i.[0] = '-') (fun ppf -> Format.fprintf ppf "%s") ppf i
      | Pconst_float (i, Some m) ->
        paren
          (parens && i.[0] = '-')
          (fun ppf (i, m) -> Format.fprintf ppf "%s%c" i m)
          ppf
          (i, m)

    let is_punned_labelled_pattern_no_attrs p lbl =
      match p.ppat_attributes, p.ppat_desc with
      | _ :: _, _ -> false
      | ( []
        , Ppat_constraint
            ({ ppat_desc = Ppat_var { txt; _ }; ppat_attributes = []; _ }, _) )
      | [], Ppat_var { txt; _ } ->
        txt = lbl
      | _ -> false

    let isLongIdentWithDot = function Ldot _ -> true | _ -> false

    (* Js.t -> useful for bucklescript sugar `Js.t({. foo: bar})` -> `{. "foo":
       bar}` *)
    let isJsDotTLongIdent ident =
      match ident with Ldot (Lident "Js", "t") -> true | _ -> false

    let recordRowIsPunned pld =
      let name = pld.pld_name.txt in
      match pld.pld_type with
      | { ptyp_desc =
            Ptyp_constr
              ( { txt; _ }
              , (* don't pun parameterized types, e.g. {tag: tag 'props} *)
                [] )
        ; (* Don't pun types that have attributes attached, e.g. { foo: [@bar]
             foo } *)
          ptyp_attributes = []
        ; _
        }
        when Longident.last_exn txt = name
             (* Don't pun types from other modules, e.g. type bar = {foo:
                Baz.foo}; *)
             && isLongIdentWithDot txt == false ->
        true
      | _ -> false

    let isPunnedJsxArg lbl ident =
      (not (isLongIdentWithDot ident.txt)) && Longident.last_exn ident.txt = lbl

    let is_unit_pattern x =
      match x.ppat_desc with
      | Ppat_construct ({ txt = Lident "()"; _ }, None) -> true
      | _ -> false

    let is_ident_pattern x =
      match x.ppat_desc with Ppat_var _ -> true | _ -> false

    let is_any_pattern x = x.ppat_desc = Ppat_any

    let is_direct_pattern x =
      x.ppat_attributes == []
      &&
      match x.ppat_desc with
      | Ppat_construct ({ txt = Lident "()"; _ }, None) -> true
      | _ -> false

    let isJSXComponent expr =
      match expr with
      | { pexp_desc = Pexp_apply ({ pexp_desc = Pexp_ident _; _ }, args)
        ; pexp_attributes
        ; _
        }
      | { pexp_desc =
            Pexp_apply ({ pexp_desc = Pexp_letmodule (_, _, _); _ }, args)
        ; pexp_attributes
        ; _
        } ->
        let { Reason_attributes.jsxAttrs; _ } =
          Reason_attributes.partitionAttributes pexp_attributes
        in
        let hasLabelledChildrenLiteral =
          List.exists
            (function Labelled "children", _ -> true | _ -> false)
            args
        in
        let rec hasSingleNonLabelledUnitAndIsAtTheEnd l =
          match l with
          | [] -> false
          | ( Nolabel
            , { pexp_desc = Pexp_construct ({ txt = Lident "()"; _ }, _); _ } )
            :: [] ->
            true
          | (Nolabel, _) :: _ -> false
          | _ :: rest -> hasSingleNonLabelledUnitAndIsAtTheEnd rest
        in
        if
          jsxAttrs != []
          && hasLabelledChildrenLiteral
          && hasSingleNonLabelledUnitAndIsAtTheEnd args
        then true
        else false
      | _ -> false

    (* Some cases require special formatting when there's a function application
     * with a single argument containing some kind of structure with braces/parens/brackets.
     * Example: `foo({a: 1, b: 2})` needs to be formatted as
     *  foo({
     *    a: 1,
     *    b: 2
     *  })
     *  when the line length dictates breaking. Notice how `({` and `})` 'hug'.
     *  Also applies to (poly)variants because they can be seen as a form of "function application".
     *  This function says if a list of expressions fulfills the need to be formatted like
     *  the example above. *)
    let isSingleArgParenApplication = function
      | [ { pexp_attributes = []; pexp_desc = Pexp_record _; _ } ]
      | [ { pexp_attributes = []; pexp_desc = Pexp_tuple _; _ } ]
      | [ { pexp_attributes = []; pexp_desc = Pexp_array _; _ } ]
      | [ { pexp_attributes = []; pexp_desc = Pexp_object _; _ } ] ->
        true
      | [ { pexp_attributes = []; pexp_desc = Pexp_extension (s, _); _ } ]
        when s.txt = "mel.obj" ->
        true
      | [ ({ pexp_attributes = []; _ } as exp) ] when is_simple_list_expr exp ->
        true
      | _ -> false

    (* Determines if the arguments of a constructor pattern match need
     * special printing. If there's one argument & they have some kind of wrapping,
     * they're wrapping need to 'hug' the surrounding parens.
     * Example:
     *  switch x {
     *  | Some({
     *      a,
     *      b,
     *    }) => ()
     *  }
     *
     *  Notice how ({ and }) hug.
     *  This applies for records, arrays, tuples & lists.
     *  See `singleArgParenPattern` for the acutal formatting
    *)
    let isSingleArgParenPattern = function
      | [ { ppat_attributes = []; ppat_desc = Ppat_record _; _ } ]
      | [ { ppat_attributes = []; ppat_desc = Ppat_array _; _ } ]
      | [ { ppat_attributes = []; ppat_desc = Ppat_tuple _; _ } ] ->
        true
      | [ { ppat_attributes = []
          ; ppat_desc = Ppat_construct ({ txt = Lident "::"; _ }, _)
          ; _
          }
        ] ->
        true
      | _ -> false

    (* Flattens a resolvedRule into a list of infixChain nodes.
     * When foo |> f |> z gets parsed, we get the following tree:
     *         |>
     *        /  \
     *    foo      |>
     *            /  \
     *          f      z
     * To format this recursive tree in a way that allows nice breaking
     * & respects the print-width, we need some kind of flattened
     * version of the above tree. `computeInfixChain` transforms the tree
     * in a flattened version which allows flexible formatting.
     * E.g. we get
     *  [LayoutNode foo; InfixToken |>; LayoutNode f; InfixToken |>; LayoutNode z]
    *)
    let rec computeInfixChain = function
      | LayoutNode layoutNode -> [ Layout layoutNode ]
      | InfixTree (op, leftResolvedRule, rightResolvedRule) ->
        computeInfixChain leftResolvedRule
        @ [ InfixToken op ]
        @ computeInfixChain rightResolvedRule

    let equalityOperators = [ "!="; "!=="; "==="; "=="; ">="; "<="; "<"; ">" ]

    (* Formats a flattened list of infixChain nodes into a list of layoutNodes
     * which allow smooth line-breaking
     * e.g. [LayoutNode foo; InfixToken |>; LayoutNode f; InfixToken |>; LayoutNode z]
     * becomes
     * [
     *   foo
     * ; |> f        --> label
     * ; |> z        --> label
     * ]
     * If you make a list out of this items, we get smooth line breaking
     *  foo |> f |> z
     * becomes
     *  foo
     *  |> f
     *  |> z
     *  when the print-width forces line breaks.
    *)
    let formatComputedInfixChain infixChainList =
      let layout_of_group group currentToken =
        (* Represents the `foo` in
         * foo
         * |> f
         * |> z *)
        match group with
        | [] | [ _ ] -> makeList ~inline:(true, true) ~sep:(Sep " ") group
        | _ ->
          (* Basic equality operators require special formatting, we can't give it
           * 'classic' infix operator formatting, otherwise we would get
           * let example =
           *  true
           *  != false
           *  && "a"
           *  == "b"
           * *)
          if List.mem currentToken equalityOperators
          then
            let hd = List.hd group in
            let tl =
              makeList ~inline:(true, true) ~sep:(Sep " ") (List.tl group)
            in
            makeList
              ~inline:(true, true)
              ~sep:(Sep " ")
              ~break:IfNeed
              [ hd; tl ]
          else if currentToken.[0] = '#'
          then
            let isSharpEqual = currentToken = sharpOpEqualToken in
            makeList ~postSpace:isSharpEqual group
          else
            (* Represents `|> f` in foo |> f
             * We need a label here to indent possible closing parens
             * on the same height as the infix operator
             * e.g.
             * >|= (
             *   fun body =>
             *     Printf.sprintf
             *       "okokok" uri meth headers body
             * )   <-- notice how this closing paren is on the same height as >|=
            *)
            label
              ~break:`Never
              ~space:true
              (atom currentToken)
              (List.nth group 1)
      in
      let rec print acc group currentToken l =
        match l with
        | x :: xs ->
          (match x with
          | InfixToken t ->
            (* = or := *)
            if List.mem t requireIndentFor
            then
              let groupNode =
                makeList
                  ~inline:(true, true)
                  ~sep:(Sep " ")
                  (print [] group currentToken [] @ [ atom t ])
              in
              let children =
                makeList
                  ~inline:(true, true)
                  ~preSpace:true
                  ~break:IfNeed
                  (print [] [] t xs)
              in
              print (acc @ [ label ~space:true groupNode children ]) [] t []
              (* Represents:
               * List.map @@
               * List.length
               *
               * Notice how we want the `@@` on the first line.
               * Extra indent puts pressure on the subsequent line lengths
               * *)
            else if t = "@@"
            then
              let groupNode =
                makeList ~inline:(true, true) ~sep:(Sep " ") (group @ [ atom t ])
              in
              print (acc @ [ groupNode ]) [] t xs
              (* != !== === == >= <= < > etc *)
            else if List.mem t equalityOperators
            then print acc (print [] group currentToken [] @ [ atom t ]) t xs
            else if requireNoSpaceFor t
            then
              if currentToken = "" || requireNoSpaceFor currentToken
              then print acc (group @ [ atom t ]) t xs
              else
                (* a + b + foo##bar##baz
                 * `foo` needs to be picked from the current group
                 * and inserted into a new one. This way `foo`
                 * gets the special "chained"-printing:
                 * foo##bar##baz. *)
                match List.rev group with
                | hd :: tl ->
                  let acc =
                    acc @ [ layout_of_group (List.rev tl) currentToken ]
                  in
                  print acc [ hd; atom t ] t xs
                | [] -> print acc (group @ [ atom t ]) t xs
            else
              print
                (acc @ [ layout_of_group group currentToken ])
                [ atom t ]
                t
                xs
          | Layout layoutNode ->
            print acc (group @ [ layoutNode ]) currentToken xs)
        | [] ->
          if List.mem currentToken requireIndentFor
          then acc @ group
          else acc @ [ layout_of_group group currentToken ]
      in
      let l = print [] [] "" infixChainList in
      makeList ~inline:(true, true) ~sep:(Sep " ") ~break:IfNeed l

    (** * [groupAndPrint] will print every item in [items] according to the
        function [xf]. * [getLoc] will extract the location from an item. Based
        on the difference * between the location of two items, if there's
        whitespace between the two * (taken possible comments into account),
        items get grouped. * Every group designates a series of layout nodes "in
        need * of whitespace above". A group gets decorated with a Whitespace
        node * containing enough info to interleave whitespace at a later time
        during * printing. *)
    let groupAndPrint ~xf ~getLoc ~comments items =
      let rec group prevLoc curr acc = function
        (* group items *)
        | x :: xs ->
          let item = xf x in
          let loc = getLoc x in
          (* Get the range between the current and previous item
           * Example:
           * 1| let a = 1;
           * 2|            --> this is the range between the two
           * 3| let b = 2;
           * *)
          let range = Range.makeRangeBetween prevLoc loc in
          (* If there's whitespace interleaved, append the new layout node
           * to a new group, otherwise keep it in the current group.
           * Takes possible comments interleaved into account.
           *
           * Example:
           * 1| let a = 1;
           * 2|
           * 3| let b = 2;
           * 4| let c = 3;
           * `let b = 2` will mark the start of a new group
           * `let c = 3` will be added to the group containing `let b = 2`
          *)
          if Range.containsWhitespace ~range ~comments ()
          then group loc [ range, item ] (List.rev curr :: acc) xs
          else group loc ((range, item) :: curr) acc xs
        (* convert groups into "Layout.Whitespace" *)
        | [] ->
          let groups = List.rev (List.rev curr :: acc) in
          List.mapi
            (fun i group ->
               match group with
               | curr :: xs ->
                 let range, x = curr in
                 (* if this is the first group of all "items", the number of
                  * newlines interleaved should be 0, else we collapse all newlines
                  * to 1.
                  *
                  * Example:
                  * module Abc = {
                  *   let a = 1;
                  *
                  *   let b = 2;
                  * }
                  * `let a = 1` should be wrapped in a `Layout.Whitespace` because a
                  * user might put comments above the `let a = 1`.
                  * e.g.
                  * module Abc = {
                  *   /* comment 1 */
                  *
                  *   /* comment 2 */
                  *   let a = 1;
                  *
                  *  A Whitespace-node will automatically take care of the whitespace
                  *  interleaving between the comments.
                 *)
                 let newlines = if i > 0 then 1 else 0 in
                 let region = WhitespaceRegion.make ~range ~newlines () in
                 let firstLayout = Layout.Whitespace (region, x) in
                 (* the first layout node of every group taks care of the
                  * whitespace above a group*)
                 firstLayout :: List.map snd xs
               | [] -> [])
            groups
      in
      match items with
      | first :: rest ->
        List.concat (group (getLoc first) [] [] (first :: rest))
      | [] -> []

    let printer =
      object (self : 'self)
        val pipe = false
        val semi = false
        val inline_braces = false
        val preserve_braces = true

        (* *Mutable state* in the printer to keep track of all comments
         * Used when whitespace needs to be interleaved.
         * The printing algorithm needs to take the comments into account in between
         * two items, to correctly determine if there's whitespace between two items.
         * The ast doesn't know if there are comments between two items, since
         * comments are store separately. The location diff between two items
         * might indicate whitespace between the two. While in reality there are
         * comments filling that whitespace. The printer needs access to the comments
         * for this reason.
         *
         * Example:
         * 1| let a = 1;
         * 2|
         * 3|
         * 4| let b = 2;
         *  -> here we can just diff the locations between `let a = 1` and `let b = 2`
         *
         * 1| let a = 1;
         * 2| /* a comment */
         * 3| /* another comment */
         * 4| let b = 2;
         *  -> here the location diff will result into false info if we don't include
         *  the comments in the diffing
        *)
        val mutable comments = []
        method comments = comments
        method trackComment comment = comments <- comment :: comments

        (* The test and first branch of ternaries must be guarded *)
        method under_pipe = {<pipe = true>}
        method under_semi = {<semi = true>}
        method reset_semi = {<semi = false>}
        method reset_pipe = {<pipe = false>}
        method reset = {<pipe = false; semi = false>}
        method inline_braces = {<inline_braces = true>}
        method dont_preserve_braces = {<preserve_braces = false>}

        method reset_request_braces =
          {<inline_braces = false; preserve_braces = true>}

        method longident =
          function
          | Lident s -> protectIdentifier s
          | Ldot (longPrefix, s) ->
            protectLongIdentifier (self#longident longPrefix) s
          | Lapply (y, s) ->
            makeList [ self#longident y; atom "("; self#longident s; atom ")" ]

        (* This form allows applicative functors. *)
        method longident_class_or_type_loc x = self#longident x.txt

        (* TODO: Fail if observing applicative functors for this form. *)
        method longident_loc (x : Longident.t Location.loc) =
          source_map ~loc:x.loc (self#longident x.txt)

        method constant ?raw_literal ?(parens = true) =
          wrap (constant ?raw_literal ~parens)

        method constant_string_for_primitive =
          wrap constant_string_for_primitive

        method tyvar = wrap tyvar

        (* c ['a,'b] *)
        method class_params_def =
          function [] -> atom "" | l -> makeTup (List.map self#type_param l)

        (* This will fall through to the simple version. *)
        method non_arrowed_core_type x = self#non_arrowed_non_simple_core_type x

        method core_type2 x =
          let { Reason_attributes.stdAttrs; uncurried; _ } =
            Reason_attributes.partitionAttributes x.ptyp_attributes
          in
          let uncurried =
            uncurried
            ||
            try Hashtbl.find uncurriedTable x.ptyp_loc with
            | Not_found -> false
          in
          if stdAttrs != []
          then
            formatAttributed
              (self#non_arrowed_simple_core_type
                 { x with ptyp_attributes = [] })
              (self#attributes stdAttrs)
          else
            let x = if uncurried then { x with ptyp_attributes = [] } else x in
            match x.ptyp_desc with
            | Ptyp_arrow _ ->
              let rec allArrowSegments ?(uncurried = false) acc = function
                | { ptyp_desc = Ptyp_arrow (l, ct1, ct2)
                  ; ptyp_attributes = []
                  ; _
                  } ->
                  allArrowSegments
                    ~uncurried:false
                    ((l, ct1, false || uncurried) :: acc)
                    ct2
                | rhs ->
                  let rhs = self#core_type2 rhs in
                  let is_tuple typ =
                    match typ.ptyp_desc with Ptyp_tuple _ -> true | _ -> false
                  in
                  (match acc with
                  | [ (Nolabel, lhs, uncurried) ] when not (is_tuple lhs) ->
                    let t = self#non_arrowed_simple_core_type lhs in
                    let lhs =
                      if uncurried
                      then makeList ~wrap:("(. ", ")") ~postSpace:true [ t ]
                      else t
                    in
                    lhs, rhs
                  | acc ->
                    let params = List.rev_map self#type_with_label acc in
                    makeCommaBreakableListSurround "(" ")" params, rhs)
              in
              let lhs, rhs = allArrowSegments ~uncurried [] x in
              let normalized =
                makeList
                  ~preSpace:true
                  ~postSpace:true
                  ~inline:(true, true)
                  ~break:IfNeed
                  ~sep:(Sep "=>")
                  [ lhs; rhs ]
              in
              source_map ~loc:x.ptyp_loc normalized
            | Ptyp_poly (sl, ct) ->
              let ct = self#core_type ct in
              let poly =
                match sl with
                | [] -> ct
                | sl ->
                  makeList
                    ~break:IfNeed
                    ~postSpace:true
                    [ makeList
                        [ makeList
                            ~postSpace:true
                            (List.map (fun { txt; _ } -> self#tyvar txt) sl)
                        ; atom "."
                        ]
                    ; ct
                    ]
              in
              source_map ~loc:x.ptyp_loc poly
            | _ -> self#non_arrowed_core_type x

        (* Same as core_type2 but can be aliased *)
        method core_type x =
          let { Reason_attributes.stdAttrs; uncurried; _ } =
            Reason_attributes.partitionAttributes x.ptyp_attributes
          in
          let () =
            if uncurried then Hashtbl.add uncurriedTable x.ptyp_loc true
          in
          if stdAttrs != []
          then
            formatAttributed
              (self#non_arrowed_simple_core_type
                 { x with ptyp_attributes = [] })
              (self#attributes stdAttrs)
          else
            match x.ptyp_desc with
            | Ptyp_alias (ct, s) ->
              source_map
                ~loc:x.ptyp_loc
                (label
                   ~space:true
                   (self#core_type ct)
                   (makeList ~postSpace:true [ atom "as"; atom ("'" ^ s) ]))
            | _ -> self#core_type2 x

        method type_with_label (lbl, c, uncurried) =
          let typ = self#core_type c in
          let t =
            match lbl with
            | Nolabel -> typ
            | Labelled lbl ->
              label ~space:true (atom (namedArgSym ^ lbl ^ ":")) typ
            | Optional lbl ->
              label
                ~space:true
                (atom (namedArgSym ^ lbl ^ ":"))
                (label typ (atom "=?"))
          in
          if uncurried then makeList ~postSpace:true [ atom "."; t ] else t

        method type_param (ct, (a, _)) =
          makeList [ atom (type_variance a); self#core_type ct ]

        (* According to the parse rule [type_declaration], the "type declaration"'s
         * physical location (as indicated by [td.ptype_loc]) begins with the
         * identifier and includes the constraints. *)
        method formatOneTypeDef
          prepend
          name
          assignToken
          ({ ptype_params; ptype_kind; ptype_loc; _ } as td) =
          let equalInitiatedSegments, constraints =
            self#type_declaration_binding_segments td
          in
          let formattedTypeParams = List.map self#type_param ptype_params in
          let binding = makeList ~postSpace:true [ prepend; name ] in

          (*    /-----------everythingButConstraints--------------  | -constraints--\
           *   /-innerL---| ------innerR--------------------------\
           *  /binding\     /typeparams\ /--equalInitiatedSegments-\
           *  type name      'v1    'v1  =  foo = private bar        constraint a = b
          *)
          let labelWithParams =
            match formattedTypeParams with
            | [] -> binding
            | l -> label binding (makeTup l)
          in
          let everythingButConstraints =
            let nameParamsEquals =
              makeList ~postSpace:true [ labelWithParams; assignToken ]
            in
            match equalInitiatedSegments with
            | [] -> labelWithParams
            | _ :: _ :: _ :: _ ->
              raise (NotPossible "More than two type segments.")
            | hd :: [] ->
              formatAttachmentApplication
                typeApplicationFinalWrapping
                (Some (true, nameParamsEquals))
                (hd, None)
            | [ hd; hd2 ] ->
              let first =
                makeList
                  ~postSpace:true
                  ~break:IfNeed
                  ~inline:(true, true)
                  (hd @ [ atom "=" ])
              in
              (* Because we want a record as a label with the opening brace on the same line
               * and the closing brace indented at the beginning, we can't wrap it in a list here
               * Example:
               * type doubleEqualsRecord =
               *  myRecordWithReallyLongName = {   <- opening brace on the same line
               *    xx: int,
               *    yy: int
               *  };                               <- closing brace indentation
              *)
              let second =
                match ptype_kind with
                | Ptype_record _ -> List.hd hd2
                | _ ->
                  makeList
                    ~postSpace:true
                    ~break:IfNeed
                    ~inline:(true, true)
                    hd2
              in
              label
                ~space:true
                nameParamsEquals
                (label ~space:true first second)
          in
          let everything =
            match constraints with
            | [] -> everythingButConstraints
            | hd :: tl ->
              makeList
                ~break:IfNeed
                ~postSpace:true
                ~indent:0
                ~inline:(true, true)
                (everythingButConstraints :: hd :: tl)
          in
          source_map ~loc:ptype_loc everything

        method formatOneTypeExt prepend name assignToken te =
          let privateAtom = atom "pri" in
          let privatize scope lst =
            match scope with Public -> lst | Private -> privateAtom :: lst
          in
          let equalInitiatedSegments =
            let segments =
              List.map
                self#type_extension_binding_segments
                te.ptyext_constructors
            in
            let privatized_segments = privatize te.ptyext_private segments in
            [ makeList
                ~break:Always_rec
                ~postSpace:true
                ~inline:(true, true)
                privatized_segments
            ]
          in
          let formattedTypeParams = List.map self#type_param te.ptyext_params in
          let binding = makeList ~postSpace:true [ prepend; name ] in
          let labelWithParams =
            match formattedTypeParams with
            | [] -> binding
            | l -> label binding (makeTup l)
          in
          let everything =
            let nameParamsEquals =
              makeList ~postSpace:true [ labelWithParams; assignToken ]
            in
            formatAttachmentApplication
              typeApplicationFinalWrapping
              (Some (true, nameParamsEquals))
              (equalInitiatedSegments, None)
          in
          source_map ~loc:te.ptyext_path.loc everything

        method type_extension_binding_segments
          { pext_kind; pext_loc; pext_attributes; pext_name } =
          let normalize lst =
            match lst with
            | [] -> raise (NotPossible "should not be called")
            | [ hd ] -> hd
            | _ :: _ -> makeList lst
          in
          let add_bar name attrs args =
            let lbl =
              match args with None -> name | Some args -> label name args
            in
            if attrs != []
            then
              label
                ~space:true
                (makeList
                   ~postSpace:true
                   [ atom "|"
                   ; makeList
                       ~postSpace:true
                       ~break:Layout.IfNeed
                       ~inline:(true, true)
                       (self#attributes attrs)
                   ])
                lbl
            else makeList ~postSpace:true [ atom "|"; lbl ]
          in
          let sourceMappedName = atom ~loc:pext_name.loc pext_name.txt in
          let resolved =
            match pext_kind with
            | Pext_decl (_, ctor_args, gadt) ->
              let formattedArgs =
                match ctor_args with
                | Pcstr_tuple [] -> []
                | Pcstr_tuple args ->
                  [ makeTup
                      (List.map self#non_arrowed_non_simple_core_type args)
                  ]
                | Pcstr_record r ->
                  [ self#record_declaration ~wrap:("({", "})") r ]
              in
              let formattedGadt =
                match gadt with
                | None -> None
                | Some x ->
                  Some
                    (makeList
                       [ formatJustTheTypeConstraint (self#core_type x) ])
              in
              formattedArgs, formattedGadt
            (* type bar += Foo = Attr.Foo *)
            | Pext_rebind rebind ->
              let r = self#longident_loc rebind in
              (* we put an empty space before the '=': we don't have access to the fact
               * that we need a space because of the Pext_rebind later *)
              let prepend = atom " =" in
              [ makeList ~postSpace:true [ prepend; r ] ], None
          in
          (*
             *  The first element of the tuple represents constructor arguments,
           *  the second an optional formatted gadt.
           *
           *  Case 1: No constructor arguments, neither a gadt
           *    type attr = ..;
           *    type attr += | Str
           *
           *  Case 2: No constructor arguments, is a gadt
           *    type attr = ..;
           *    type attr += | Str :attr
           *
           *  Case 3: Has Constructor args, not a gadt
           *    type attr  = ..;
           *    type attr += | Str(string);
           *    type attr += | Point(int, int);
           *
           *  Case 4: Has Constructor args & is a gadt
           *    type attr  = ..;
           *    type attr += | Point(int, int) :attr;
          *)
          let everything =
            match resolved with
            | [], None -> add_bar sourceMappedName pext_attributes None
            | [], Some gadt ->
              add_bar sourceMappedName pext_attributes (Some gadt)
            | ctorArgs, None ->
              add_bar
                sourceMappedName
                pext_attributes
                (Some (normalize ctorArgs))
            | ctorArgs, Some gadt ->
              add_bar
                sourceMappedName
                pext_attributes
                (Some (normalize (ctorArgs @ [ gadt ])))
          in
          source_map ~loc:pext_loc everything

        (* shared by [Pstr_type, Psig_type]*)
        method type_def_list ?(eq_symbol = "=") ?extension rf l =
          (* As oposed to used in type substitution. *)
          let formatOneTypeDefStandard prepend td =
            let itm =
              self#formatOneTypeDef
                prepend
                (atom ~loc:td.ptype_name.loc td.ptype_name.txt)
                (atom eq_symbol)
                td
            in
            let { Reason_attributes.stdAttrs; docAttrs; _ } =
              Reason_attributes.partitionAttributes
                ~partDoc:true
                td.ptype_attributes
            in
            let layout = self#attach_std_item_attrs stdAttrs itm in
            self#attachDocAttrsToLayout
              ~stdAttrs
              ~docAttrs
              ~loc:td.ptype_loc
              ~layout
              ()
          in

          match l with
          | [] -> raise (NotPossible "asking for type list of nothing")
          | hd :: tl ->
            let first =
              match rf with
              | Recursive ->
                let label = add_extension_sugar "type" extension in
                formatOneTypeDefStandard (atom label) hd
              | Nonrecursive -> formatOneTypeDefStandard (atom "type nonrec") hd
            in
            (match tl with
            (* Exactly one type *)
            | [] -> first
            | _ :: _ as typeList ->
              let items =
                (hd.ptype_loc, first)
                :: List.map
                     (fun ptyp ->
                        ( ptyp.ptype_loc
                        , formatOneTypeDefStandard (atom "and") ptyp ))
                     typeList
              in
              makeList
                ~indent:0
                ~inline:(true, true)
                ~break:Always_rec
                (groupAndPrint
                   ~xf:snd
                   ~getLoc:fst
                   ~comments:self#comments
                   items))

        method type_variant_list lst =
          match lst with
          | [] -> [ atom "|" ]
          | _ -> List.map (fun x -> self#type_variant_leaf x) lst

        method type_variant_leaf
          ?opt_ampersand:(a = false)
          ?polymorphic:(p = false) =
          self#type_variant_leaf1 a p true

        method type_variant_leaf_nobar
          ?opt_ampersand:(a = false)
          ?polymorphic:(p = false) =
          self#type_variant_leaf1 a p false

        (* TODOATTRIBUTES: Attributes on the entire variant leaf are likely
         * not parsed or printed correctly. *)
        method type_variant_leaf1 opt_ampersand polymorphic print_bar x =
          let { pcd_name; pcd_args; pcd_res; pcd_loc; pcd_attributes; _ } = x in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes ~partDoc:true pcd_attributes
          in
          let ampersand_helper i arg =
            let ct = self#core_type arg in
            let ct =
              match arg.ptyp_desc with
              | Ptyp_tuple _ -> ct
              | _ -> makeTup [ ct ]
            in
            if i == 0 && not opt_ampersand then ct else label (atom "&") ct
          in
          let args =
            match pcd_args with
            | Pcstr_record r -> [ self#record_declaration ~wrap:("({", "})") r ]
            | Pcstr_tuple [] -> []
            | Pcstr_tuple l when polymorphic -> List.mapi ampersand_helper l
            (* Here's why this works. With the new syntax, all the args, are
               already inside of a safely guarded place like Constructor(here,
               andHere). Compare that to the previous syntax Constructor here
               andHere. In the previous syntax, we needed to require that we
               print "non-arrowed" types for here, and andHere to avoid
               something like Constructor a=>b c=>d. In the new syntax, we don't
               care if here and andHere have unguarded arrow types like a=>b
               because they're safely separated by commas. *)
            | Pcstr_tuple l -> [ makeTup (List.map self#core_type l) ]
          in
          let gadtRes =
            match pcd_res with
            | None -> None
            | Some x -> Some (formatJustTheTypeConstraint (self#core_type x))
          in
          let normalize lst =
            match lst with
            | [] -> raise (NotPossible "should not be called")
            | [ hd ] -> hd
            | _ :: _ ->
              makeList ~inline:(true, true) ~break:IfNeed ~postSpace:true lst
          in
          let add_bar constructor =
            makeList
              ~postSpace:true
              (if print_bar then [ atom "|"; constructor ] else [ constructor ])
          in
          (* In some cases (e.g. inline records) we want the label with bar & the gadt resolution
           * as a list.
           *   | If {
           *       pred: expr bool,
           *       true_branch: expr 'a,
           *       false_branch: expr 'a
           *     }                           ==> end of label
           *     :expr 'a;                   ==> gadt res
           * The label & the gadt res form two separate units combined into a list.
           * This is necessary to properly align the closing '}' on the same height as the 'If'.
          *)
          let add_bar_2 ?gadt name args =
            let lbl = label name args in
            let fullLbl =
              match gadt with
              | Some g -> makeList ~inline:(true, true) ~break:IfNeed [ lbl; g ]
              | None -> lbl
            in
            add_bar fullLbl
          in

          let prefix = if polymorphic then "`" else "" in
          let sourceMappedName =
            atom ~loc:pcd_name.loc (prefix ^ pcd_name.txt)
          in
          let sourceMappedNameWithAttributes =
            let layout =
              match stdAttrs with
              | [] -> sourceMappedName
              | stdAttrs ->
                formatAttributed sourceMappedName (self#attributes stdAttrs)
            in
            match docAttrs with
            | [] -> layout
            | docAttrs ->
              makeList
                ~break:Always
                ~inline:(true, true)
                [ makeList (self#attributes docAttrs); layout ]
          in
          let constructorName =
            makeList ~postSpace:true [ sourceMappedNameWithAttributes ]
          in
          let everything =
            match args, gadtRes with
            | [], None -> add_bar sourceMappedNameWithAttributes
            | [], Some gadt -> add_bar_2 sourceMappedNameWithAttributes gadt
            | _ :: _, None -> add_bar_2 constructorName (normalize args)
            | _ :: _, Some gadt ->
              (match pcd_args with
              | Pcstr_record _ ->
                add_bar_2 ~gadt constructorName (normalize args)
              | _ -> add_bar_2 constructorName ~gadt (normalize args))
          in
          source_map ~loc:pcd_loc everything

        method record_declaration ?(wrap = "{", "}") ?assumeRecordLoc lbls =
          let recordRow pld =
            let hasPunning = recordRowIsPunned pld in
            let name =
              if hasPunning
              then [ atom pld.pld_name.txt ]
              else [ atom pld.pld_name.txt; atom ":" ]
            in
            let name = source_map ~loc:pld.pld_name.loc (makeList name) in
            let withMutable =
              match pld.pld_mutable with
              | Immutable -> name
              | Mutable -> makeList ~postSpace:true [ atom "mutable"; name ]
            in
            let recordRow =
              if hasPunning
              then label withMutable (atom "")
              else label ~space:true withMutable (self#core_type pld.pld_type)
            in
            let recordRow =
              match pld.pld_attributes with
              | [] -> recordRow
              | attrs ->
                let { Reason_attributes.stdAttrs; docAttrs; _ } =
                  Reason_attributes.partitionAttributes ~partDoc:true attrs
                in
                let stdAttrsLayout =
                  makeList
                    ~inline:(true, true)
                    ~postSpace:true
                    (self#attributes stdAttrs)
                in
                let docAttrsLayout =
                  makeList ~inline:(true, true) (self#attributes docAttrs)
                in
                let children =
                  match docAttrs, stdAttrs with
                  | [], [] -> [ recordRow ]
                  | _, [] -> [ docAttrsLayout; recordRow ]
                  | [], _ -> [ stdAttrsLayout; recordRow ]
                  | _, _ -> [ docAttrsLayout; stdAttrsLayout; recordRow ]
                in
                makeList ~inline:(true, true) ~break:Always_rec children
            in
            source_map ~loc:pld.pld_loc recordRow
          in
          let rows = List.map recordRow lbls in
          (* if a record type has more than 1 row, always break *)
          let break =
            match rows with
            | [] | [ _ ] -> Layout.IfNeed
            | _ -> Layout.Always_rec
          in
          source_map
            ?loc:assumeRecordLoc
            (makeList ~wrap ~sep:commaTrail ~postSpace:true ~break rows)

        (* Returns the type declaration partitioned into three segments - one
           suitable for appending to a label, the actual type manifest and the
           list of constraints. *)
        method type_declaration_binding_segments x =
          (* Segments of the type binding (occuring after the type keyword) that
           * should begin with "=". Zero to two total sections.
           * This is just a straightforward reverse mapping from the original parser:
           *  type_kind:
           *      /*empty*/
           *        { (Ptype_abstract, Public, None) }
           *    | EQUAL core_type
           *        { (Ptype_abstract, Public, Some $2) }
           *    | EQUAL PRIVATE core_type
           *        { (Ptype_abstract, Private, Some $3) }
           *    | EQUAL constructor_declarations
           *        { (Ptype_variant(List.rev $2), Public, None) }
           *    | EQUAL PRIVATE constructor_declarations
           *        { (Ptype_variant(List.rev $3), Private, None) }
           *    | EQUAL private_flag BAR constructor_declarations
           *        { (Ptype_variant(List.rev $4), $2, None) }
           *    | EQUAL DOTDOT
           *        { (Ptype_open, Public, None) }
           *    | EQUAL private_flag LBRACE label_declarations opt_comma RBRACE
           *        { (Ptype_record(List.rev $4), $2, None) }
           *    | EQUAL core_type EQUAL private_flag opt_bar constructor_declarations
           *        { (Ptype_variant(List.rev $6), $4, Some $2) }
           *    | EQUAL core_type EQUAL DOTDOT
           *        { (Ptype_open, Public, Some $2) }
           *    | EQUAL core_type EQUAL private_flag LBRACE label_declarations opt_comma RBRACE
           *        { (Ptype_record(List.rev $6), $4, Some $2) }
          *)
          let privateAtom = atom "pri" in
          let privatize scope lst =
            match scope with Public -> lst | Private -> privateAtom :: lst
          in

          let estimateRecordOpenBracePoint () =
            match x.ptype_params with
            | [] -> x.ptype_name.loc.loc_end
            | _ ->
              (fst (List.nth x.ptype_params (List.length x.ptype_params - 1)))
                .ptyp_loc
                .loc_end
          in

          let equalInitiatedSegments =
            match x.ptype_kind, x.ptype_private, x.ptype_manifest with
            (* /*empty*/ {(Ptype_abstract, Public, None)} *)
            | Ptype_abstract, Public, None -> []
            (* EQUAL core_type {(Ptype_abstract, Public, Some _)} *)
            | Ptype_abstract, Public, Some y -> [ [ self#core_type y ] ]
            (* EQUAL PRIVATE core_type {(Ptype_abstract, Private, Some $3)} *)
            | Ptype_abstract, Private, Some y ->
              [ [ privateAtom; self#core_type y ] ]
            (* EQUAL constructor_declarations {(Ptype_variant _., Public, None)} *)
            (* This case is redundant *)
            (* | (Ptype_variant lst, Public, None) -> [ *)
            (*     [makeSpacedBreakableInlineList (List.map type_variant_leaf lst)] *)
            (*   ] *)
            (* EQUAL PRIVATE constructor_declarations {(Ptype_variant _, Private, None)} *)
            | Ptype_variant lst, Private, None ->
              [ [ privateAtom
                ; makeList
                    ~break:IfNeed
                    ~postSpace:true
                    ~inline:(true, true)
                    (self#type_variant_list lst)
                ]
              ]
            (* EQUAL private_flag BAR constructor_declarations {(Ptype_variant
               _, $2, None)} *)
            | Ptype_variant lst, scope, None ->
              [ privatize
                  scope
                  [ makeList
                      ~break:Always_rec
                      ~postSpace:true
                      ~inline:(true, true)
                      (self#type_variant_list lst)
                  ]
              ]
            (* EQUAL DOTDOT {(Ptype_open, Public, None)} *)
            | Ptype_open, Public, None -> [ [ atom ".." ] ]
            | Ptype_open, Private, None -> [ [ privateAtom; atom ".." ] ]
            (* Super confusing how record/variants' manifest is not actually the
               description of the structure. What's in the manifest in that case
               is the *second* EQUALS asignment. *)
            (* EQUAL private_flag LBRACE label_declarations opt_comma RBRACE
               {(Ptype_record _, $2, None)} *)
            | Ptype_record lst, scope, None ->
              let assumeRecordLoc =
                { loc_start = estimateRecordOpenBracePoint ()
                ; loc_end = x.ptype_loc.loc_end
                ; loc_ghost = false
                }
              in
              [ privatize scope [ self#record_declaration ~assumeRecordLoc lst ]
              ]
            (* And now all of the forms involving *TWO* equals *)
            (* Again, super confusing how manifests of variants/records
               represent the structure after the second equals. *)
            (* ================================================*)

            (* EQUAL core_type EQUAL private_flag opt_bar
               constructor_declarations { (Ptype_variant _, _, Some _)} *)
            | Ptype_variant lst, scope, Some mani ->
              [ [ self#core_type mani ]
              ; (let variant =
                   makeList
                     ~break:IfNeed
                     ~postSpace:true
                     ~inline:(true, true)
                     (self#type_variant_list lst)
                 in
                 privatize scope [ variant ])
              ]
            (* EQUAL core_type EQUAL DOTDOT {(Ptype_open, Public, Some $2)} *)
            | Ptype_open, Public, Some mani ->
              [ [ self#core_type mani ]; [ atom ".." ] ]
            (* EQUAL core_type EQUAL private_flag LBRACE label_declarations
               opt_comma RBRACE {(Ptype_record _, $4, Some $2)} *)
            | Ptype_record lst, scope, Some mani ->
              let declaration = self#record_declaration lst in
              let record =
                match scope with
                | Public -> [ declaration ]
                | Private -> [ label ~space:true privateAtom declaration ]
              in
              [ [ self#core_type mani ]; record ]
            (* Everything else is impossible *)
            (* ================================================*)
            | _, _, _ ->
              raise (NotPossible "Encountered impossible type specification")
          in

          let makeConstraint (ct1, ct2, _) =
            let constraintEq =
              makeList
                ~postSpace:true
                [ atom "constraint"; self#core_type ct1; atom "=" ]
            in
            label ~space:true constraintEq (self#core_type ct2)
          in
          let constraints = List.map makeConstraint x.ptype_cstrs in
          equalInitiatedSegments, constraints

        (* "non-arrowed" means "a type where all arrows are inside at least one level of parens"
         *
         * z => z: not a "non-arrowed" type.
         * (a, b): a "non-arrowed" type.
         * (z=>z): a "non-arrowed" type because the arrows are guarded by parens.
         *
         * A "non arrowed, non simple" type would be one that is not-arrowed, and also
         * not "simple". Simple means it is "clearly one unit" like (a, b), identifier,
         * "hello", None.
        *)
        method non_arrowed_non_simple_core_type x =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.ptyp_attributes
          in
          if stdAttrs != []
          then
            formatAttributed
              (self#non_arrowed_simple_core_type
                 { x with ptyp_attributes = [] })
              (self#attributes stdAttrs)
          else
            match x.ptyp_desc with
            (* This significantly differs from the standard OCaml
               printer/parser: Type constructors are no longer simple *)
            | _ -> self#non_arrowed_simple_core_type x

        method type_param_list_element =
          function
          | { ptyp_attributes = []; ptyp_desc = Ptyp_package (lid, cstrs); _ }
            ->
            self#typ_package ~mod_prefix:true lid cstrs
          | t -> self#core_type t

        method non_arrowed_simple_core_type x =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.ptyp_attributes
          in
          if stdAttrs != []
          then
            formatSimpleAttributed
              (self#non_arrowed_simple_core_type
                 { x with ptyp_attributes = [] })
              (self#attributes stdAttrs)
          else
            let result =
              match x.ptyp_desc with
              (*   LPAREN core_type_comma_list RPAREN %prec below_NEWDOT *)
              (*       { match $2 with *)
              (*         | [] -> raise Parse_error *)
              (*         | one::[] -> one *)
              (*         | moreThanOne -> mktyp(Ptyp_tuple(List.rev moreThanOne)) } *)
              | Ptyp_tuple l ->
                makeTup (List.map self#type_param_list_element l)
              | Ptyp_object (l, o) -> self#unparseObject l o
              | Ptyp_package (lid, cstrs) ->
                self#typ_package ~protect:true ~mod_prefix:true lid cstrs
              (*   | QUOTE ident *)
              (*       { mktyp(Ptyp_var $2) } *)
              | Ptyp_var s -> ensureSingleTokenSticksToLabel (self#tyvar s)
              (*   | UNDERSCORE *)
              (*       { mktyp(Ptyp_any) } *)
              | Ptyp_any -> ensureSingleTokenSticksToLabel (atom "_")
              (*   | type_longident *)
              (*       { mktyp(Ptyp_constr(mkrhs $1 1, [])) } *)
              | Ptyp_constr (li, []) ->
                (* [ensureSingleTokenSticksToLabel] loses location information
                   which is important when you are embedded inside a list and
                   comments are to be interleaved around you. Therefore, we wrap
                   the result in the correct [SourceMap]. *)
                source_map
                  ~loc:li.loc
                  (ensureSingleTokenSticksToLabel (self#longident_loc li))
              | Ptyp_constr (li, l) ->
                (match l with
                | [ { ptyp_desc = Ptyp_object ((_ :: _ as l), o); _ } ]
                  when isJsDotTLongIdent li.txt ->
                  (* should have one or more rows, Js.t({..}) should print as Js.t({..})
                   * {..} has a totally different meaning than Js.t({..}) *)
                  self#unparseObject ~withStringKeys:true l o
                | [ { ptyp_desc = Ptyp_object (l, o); _ } ]
                  when not (isJsDotTLongIdent li.txt) ->
                  label
                    (self#longident_loc li)
                    (self#unparseObject ~wrap:("(", ")") l o)
                | [ { ptyp_desc =
                        Ptyp_constr
                          ( lii
                          , [ { ptyp_desc = Ptyp_object ((_ :: _ as ll), o); _ }
                            ] )
                    ; _
                    }
                  ]
                  when isJsDotTLongIdent lii.txt ->
                  label
                    (self#longident_loc li)
                    (self#unparseObject
                       ~withStringKeys:true
                       ~wrap:("(", ")")
                       ll
                       o)
                | _ ->
                  (* small guidance: in `type foo = bar`, we're now at the `bar`
                     part *)

                  (* The single identifier has to be wrapped in a
                     [ensureSingleTokenSticksToLabel] to avoid (@see
                     @avoidSingleTokenWrapping): *)
                  label
                    (self#longident_loc li)
                    (makeTup (List.map self#type_param_list_element l)))
              | Ptyp_variant (l, closed, low) ->
                let pcd_attributes = x.ptyp_attributes in
                let pcd_res = None in
                let variant_helper i rf =
                  match rf.prf_desc with
                  | Rtag (label, opt_ampersand, ctl) ->
                    let pcd_args = Pcstr_tuple ctl in
                    let all_attrs =
                      List.concat [ pcd_attributes; rf.prf_attributes ]
                    in
                    self#type_variant_leaf
                      ~opt_ampersand
                      ~polymorphic:true
                      { pcd_name = label
                      ; pcd_args
                      ; pcd_res
                      ; pcd_loc = label.loc
                      ; pcd_attributes = all_attrs
                      ; pcd_vars = []
                      }
                  | Rinherit ct ->
                    (* '| type' is required if the Rinherit is not the first
                       row_field in the list *)
                    if i = 0
                    then self#core_type ct
                    else
                      makeList ~postSpace:true [ atom "|"; self#core_type ct ]
                in
                let designator, tl =
                  match closed, low with
                  | Closed, None -> "", []
                  | Closed, Some tl -> "<", tl
                  | Open, _ -> ">", []
                in
                let node_list = List.mapi variant_helper l in
                let ll = List.map (fun t -> atom ("`" ^ t)) tl in
                let tag_list =
                  makeList ~postSpace:true ~break:IfNeed (atom ">" :: ll)
                in
                let type_list =
                  if tl != [] then node_list @ [ tag_list ] else node_list
                in
                let break =
                  match type_list with
                  | _ :: _ :: _ -> Layout.Always_rec
                  | [] | _ :: [] -> IfNeed
                in
                makeList
                  ~wrap:("[" ^ designator, "]")
                  ~pad:(true, false)
                  ~postSpace:true
                  ~break
                  type_list
              | Ptyp_class (li, []) ->
                makeList [ atom "#"; self#longident_loc li ]
              | Ptyp_class (li, l) ->
                label
                  (makeList [ atom "#"; self#longident_loc li ])
                  (makeTup (List.map self#core_type l))
              | Ptyp_extension e -> self#extension e
              | Ptyp_arrow (_, _, _) | Ptyp_alias (_, _) | Ptyp_poly (_, _) ->
                makeList ~wrap:("(", ")") ~break:IfNeed [ self#core_type x ]
            in
            source_map ~loc:x.ptyp_loc result
        (* TODO: ensure that we have a form of desugaring that protects *)
        (* when final argument of curried pattern is a type constraint: *)
        (* | COLON non_arrowed_core_type EQUALGREATER expr { mkexp_constraint $4
           (Some $2, None) } *)
        (*                         \----/   \--/
         *                         constraint coerce
         *
         *                         Creates a ghost expression:
         *                         mkexp_constraint | Some t, None -> ghexp(Pexp_constraint(e, t))
         *)

        method pattern_list_split_cons acc =
          function
          | { ppat_desc =
                Ppat_construct
                  ( { txt = Lident "::"; _ }
                  , Some ([], { ppat_desc = Ppat_tuple [ pat1; pat2 ]; _ }) )
            ; _
            } ->
            self#pattern_list_split_cons (pat1 :: acc) pat2
          | p -> List.rev acc, p

        (* Adds parens to the right sub-tree when it is not a single node:
         *
         * A | B                   is formatted as    A | B
         * A | (B | C)             is formatted as    A | (B | C)
         *
         * Also, adds parens to both sub-trees when both of them
         * are not a single node:
         * (A | B) | (C | D)       is formatted as    A | B | (C | D)
         * A | B | (C | D)         is formatted as    A | B | (C | D)
         * (A | B) | C             is formatted as    A | B | C
         * A | B | C               is formatted as    A | B | C
         *
        *)
        method or_pattern p1 p2 =
          let p1_raw, p2_raw = self#pattern p1, self#pattern p2 in
          let left, right =
            match p2.ppat_desc with
            | Ppat_or _ -> p1_raw, formatPrecedence p2_raw
            | _ -> p1_raw, p2_raw
          in
          makeList
            ~break:IfNeed
            ~inline:(true, true)
            ~sep:(Sep "|")
            ~postSpace:true
            ~preSpace:true
            [ left; right ]

        (* Renders level 3 or simpler patterns:
         *
         * Simpler
         * ^   -----------
         * |   1.     [ ], { }, X.{  }, ident, (any-other-pattern-with-parens-around)
         * |   2.     F(args), lazy(foo), [@attr] 1-2
         * |   3.     pat as alias, pat | pat
         * |   4.     1-3 : typ
         * v   ------------
         * Complex
         *
         * Assumes visually rendered attributes have already been rendered.
        *)
        method pattern_at_least_as_simple_as_alias_or_or x =
          let { Reason_attributes.arityAttrs = _; stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.ppat_attributes
          in
          match stdAttrs, x.ppat_desc with
          | [], Ppat_or (p1, p2) -> self#or_pattern p1 p2
          | [], Ppat_alias (p, s) ->
            let raw_pattern = self#pattern p in
            let pattern_with_precedence =
              match p.ppat_desc with
              | Ppat_or (p1, p2) -> formatPrecedence (self#or_pattern p1 p2)
              | Ppat_constraint _ -> makeList ~wrap:("(", ")") [ raw_pattern ]
              | _ -> raw_pattern
            in
            label
              ~space:true
              (source_map ~loc:p.ppat_loc pattern_with_precedence)
              (makeList
                 ~postSpace:true
                 [ atom "as"; source_map ~loc:s.loc (protectIdentifier s.txt) ])
            (* RA*)
          | _ -> self#pattern_at_least_as_simple_as_application x

        (* Formats a pattern that is a least as "simple" as function application
         * style syntax. Produces formatting that is as simple as either 1 or 2.
         *
         * Simpler
         * ^   -----------
         * |   1.     [ ], { }, X.{  }, ident, (any-other-pattern-with-parens-around)
         * |   2.     F(args), lazy(foo), [@attr] 1-2
         * |   3.     pat as alias, pat | pat
         * |   4.     1-3 : typ
         * v   ------------
         * Complex
         *
         *
         * 1. and 2. do not need parens around them in order to apply attributes to
         * them. 3. does need parens around it to apply attributes to the whole
         * pattern.
         *
         * Assumes visually rendered attributes have already been rendered.
        *)
        method pattern_at_least_as_simple_as_application x =
          (* TODOATTRIBUTES: Handle the stdAttrs here *)
          let { Reason_attributes.stdAttrs; arityAttrs; _ } =
            Reason_attributes.partitionAttributes x.ppat_attributes
          in
          let formattedPattern =
            match x.ppat_desc with
            | Ppat_variant (l, Some p) ->
              if arityAttrs != []
              then
                raise
                  (NotPossible
                     "Should never see embedded attributes on poly variant")
              else
                source_map
                  ~loc:x.ppat_loc
                  (self#constructor_pattern
                     (atom ("`" ^ l))
                     p
                     ~polyVariant:true
                     ~arityIsClear:true)
            | Ppat_lazy p ->
              label (atom "lazy") (formatPrecedence (self#simple_pattern p))
            | Ppat_construct (({ txt; _ } as li), po)
              when not (txt = Lident "::") ->
              (* FIXME The third field always false *)
              let formattedConstruction =
                match po with
                (* TODO: Check the explicit_arity field on the
                   pattern/constructor attributes to determine if should desugar
                   to an *actual* tuple. *)
                (* | Some ({ *)
                (*   ppat_desc=Ppat_tuple l; *)
                (*   ppat_attributes=[{txt="explicit_arity"; loc}] *)
                (* }) -> *)
                (* label ~space:true (self#longident_loc li)
                   (makeSpacedBreakableInlineList (List.map self#simple_pattern
                   l)) *)
                | Some (_, pattern) ->
                  let arityIsClear = isArityClear arityAttrs in
                  self#constructor_pattern
                    ~arityIsClear
                    (self#longident_loc li)
                    pattern
                | None -> self#longident_loc li
              in
              source_map ~loc:x.ppat_loc formattedConstruction
            | _ -> self#simple_pattern { x with ppat_attributes = arityAttrs }
          in
          if stdAttrs != []
          then formatAttributed formattedPattern (self#attributes stdAttrs)
          else formattedPattern

        (* Format a pattern with no particular requirements of simplicity. For example when
         * formatting a pattern *inside* one tuple position:
         *        |
         *        v
         * let (x : int, foo) = ..
         *
         *
         * Renders level 3 or simpler patterns:
         *
         * Simpler
         * ^   -----------
         * |   1.     [ ], { }, X.{  }, ident, (any-other-pattern-with-parens-around)
         * |   2.     F(args), lazy(foo), [@attr] 1-2
         * |   3.     pat as alias, pat | pat
         * |   4.     1-3 : typ
         * v   ------------
         * Complex
         *
         * Assumes visually rendered attributes have already been rendered.
        *)
        method pattern x =
          let { Reason_attributes.arityAttrs = _; stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.ppat_attributes
          in
          match stdAttrs, x.ppat_desc with
          | [], Ppat_constraint (p, ct) ->
            let pat, typ =
              match p, ct with
              | ( { ppat_desc = Ppat_unpack unpack; _ }
                , { ptyp_desc = Ptyp_package (lid, cstrs); _ } ) ->
                let unpack =
                  match unpack.txt with None -> "_" | Some unpack -> unpack
                in
                ( makeList ~postSpace:true [ atom "module"; atom unpack ]
                , self#typ_package ~mod_prefix:false lid cstrs )
              | _ ->
                (* Have to call pattern_at_least_as_simple_as_alias_or_or because
                 * we don't want to allow *another* nested type annotation without
                 * first adding parens *)
                ( self#pattern_at_least_as_simple_as_alias_or_or p
                , self#core_type ct )
            in
            formatTypeConstraint pat typ
          | _ -> self#pattern_at_least_as_simple_as_alias_or_or x

        method patternList ?(wrap = "", "") pat =
          let pat_list, pat_last = self#pattern_list_split_cons [] pat in
          let pat_list = List.map self#pattern pat_list in
          match pat_last with
          | { ppat_desc = Ppat_construct ({ txt = Lident "[]"; _ }, _); _ } ->
            (* [x,y,z] *)
            let lwrap, rwrap = wrap in
            makeList
              pat_list
              ~break:Layout.IfNeed
              ~sep:commaTrail
              ~postSpace:true
              ~wrap:(lwrap ^ "[", "]" ^ rwrap)
          | _ ->
            (* x::y *)
            makeES6List pat_list (self#pattern pat_last) ~wrap

        (* In some contexts the Ptyp_package needs to be protected by parens, or
         * the `module` keyword needs to be added.
         * Example: let f = (module Add: S.Z, x) => Add.add(x);
         *  It's clear that `S.Z` is a module because it constraints the
         *  `module Add` pattern. No need to add "module" before `S.Z`.
         *
         * Example2:
         *   type t = (module Console);
         *   In this case the "module" keyword needs to be printed to indicate
         *   usage of a first-class-module.
        *)
        method typ_package ?(protect = false) ?(mod_prefix = true) lid cstrs =
          let packageIdent =
            let packageIdent = self#longident_loc lid in
            if mod_prefix
            then makeList ~postSpace:true [ atom "module"; packageIdent ]
            else packageIdent
          in
          let unwrapped_layout =
            match cstrs with
            | [] -> packageIdent
            | cstrs ->
              label
                ~space:true
                (makeList ~postSpace:true [ packageIdent; atom "with" ])
                (makeList
                   ~inline:(true, true)
                   ~break:IfNeed
                   ~sep:(Sep " and ")
                   (List.map
                      (fun (s, ct) ->
                         label
                           ~space:true
                           (makeList
                              ~break:IfNeed
                              ~postSpace:true
                              [ atom "type"; self#longident_loc s; atom "=" ])
                           (self#core_type ct))
                      cstrs))
          in
          if protect
          then makeList ~postSpace:true ~wrap:("(", ")") [ unwrapped_layout ]
          else unwrapped_layout

        method simple_pattern x =
          let { Reason_attributes.arityAttrs; stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.ppat_attributes
          in
          if stdAttrs != []
          then
            formatSimpleAttributed
              (self#simple_pattern { x with ppat_attributes = arityAttrs })
              (self#attributes stdAttrs)
          else
            let itm =
              match x.ppat_desc with
              | Ppat_construct ({ loc; txt = Lident (("()" | "[]") as x) }, _)
                ->
                (* Patterns' locations might include a leading bar depending on the
                 * context it was parsed in. Therefore, we need to include further
                 * information about the contents of the pattern such as tokens etc,
                 * in order to get comments to be distributed correctly.*)
                atom ~loc x
              | Ppat_construct ({ txt = Lident "::"; _ }, _) ->
                self#patternList x (* LIST PATTERN *)
              | Ppat_construct (li, None) ->
                source_map ~loc:x.ppat_loc (self#longident_loc li)
              | Ppat_any -> atom "_"
              | Ppat_var { loc; txt } ->
                (* To prevent this:
                 *
                 *   let oneArgShouldWrapToAlignWith
                 *     theFunctionNameBinding => theFunctionNameBinding;
                 *
                 * And instead do:
                 *
                 *   let oneArgShouldWrapToAlignWith
                 *       theFunctionNameBinding => theFunctionNameBinding;
                 *
                 * We have to do something to the non "listy" patterns. Non listy
                 * patterns don't indent the same amount as listy patterns when docked
                 * to a label.
                 *
                 * If wrapping the non-listy pattern in [ensureSingleTokenSticksToLabel]
                 * you'll get the following (even though it should wrap)
                 *
                 *   let oneArgShouldWrapToAlignWith theFunctionNameBinding => theFunctionNameBinding;
                *)
                source_map ~loc (protectIdentifier txt)
              | Ppat_array l -> self#patternArray l
              | Ppat_unpack s ->
                let s = match s.txt with None -> "_" | Some s -> s in
                makeList
                  ~wrap:("(", ")")
                  ~break:IfNeed
                  ~postSpace:true
                  [ atom "module"; atom s ]
              | Ppat_open (lid, pat) ->
                (* let someFn Qualified.{ record } = ... *)
                let needsParens =
                  match pat.ppat_desc with
                  | Ppat_exception _ -> true
                  | _ -> false
                in
                let pat = self#simple_pattern pat in
                label
                  (label (self#longident_loc lid) (atom "."))
                  (if needsParens then formatPrecedence pat else pat)
              | Ppat_type li -> makeList [ atom "#"; self#longident_loc li ]
              | Ppat_record (l, closed) -> self#patternRecord l closed
              | Ppat_tuple l -> self#patternTuple l
              | Ppat_constant c ->
                let raw_literal, _ =
                  Reason_attributes.extract_raw_literal x.ppat_attributes
                in
                self#constant ?raw_literal c
              | Ppat_interval (c1, c2) ->
                makeList
                  ~postSpace:true
                  [ self#constant c1; atom ".."; self#constant c2 ]
              | Ppat_variant (l, None) -> makeList [ atom "`"; atom l ]
              | Ppat_constraint _ -> formatPrecedence (self#pattern x)
              | Ppat_lazy p ->
                formatPrecedence
                  (label
                     (atom "lazy")
                     (formatPrecedence (self#simple_pattern p)))
              | Ppat_extension e -> self#extension e
              | Ppat_exception p ->
                (* An exception pattern with an alias should be wrapped in (...)
                 * The rules for what goes to the right of the exception are a little (too) nuanced.
                 * It accepts "non simple" parameters, except in the case of `as`.
                 * Here we consistently apply "simplification" to the exception argument.
                 * Example:
                 *   | exception (Sys_error _ as exc) => raise exc
                 *  parses correctly while
                 *   | Sys_error _ as exc => raise exc
                 *  results in incorrect parsing with type error otherwise.
                *)
                makeList
                  ~postSpace:true
                  [ atom "exception"; self#simple_pattern p ]
              | _ -> formatPrecedence (self#pattern x)
              (* May have a redundant sourcemap *)
            in
            source_map ~loc:x.ppat_loc itm

        method label_exp lbl opt pat =
          let term = self#pattern pat in
          let param =
            match lbl with
            | Nolabel -> term
            | (Labelled lbl | Optional lbl)
              when is_punned_labelled_pattern_no_attrs pat lbl ->
              makeList [ atom namedArgSym; term ]
            | Labelled lbl | Optional lbl ->
              let lblLayout =
                makeList
                  ~sep:(Sep " ")
                  ~break:Layout.Never
                  [ atom (namedArgSym ^ lbl); atom "as" ]
              in
              label lblLayout ~space:true term
          in
          match opt, lbl with
          | None, Optional _ -> makeList [ param; atom "=?" ]
          | None, _ -> param
          | Some o, _ ->
            makeList
              [ param; atom "="; self#unparseProtectedExpr ~forceParens:true o ]

        method access op cls e1 e2 =
          makeList
            [ (* Important that this be not breaking - at least to preserve same
                 behavior as stock desugarer. It might even be required (double
                 check in parser.mly) *)
              e1
            ; atom op
            ; e2
            ; atom cls
            ]

        method simple_get_application x =
          let { Reason_attributes.stdAttrs; jsxAttrs; _ } =
            Reason_attributes.partitionAttributes x.pexp_attributes
          in
          match x.pexp_desc, stdAttrs, jsxAttrs with
          | _, _ :: _, [] -> None (* Has some printed attributes - not simple *)
          | Pexp_apply ({ pexp_desc = Pexp_ident loc; _ }, l), [], _jsx :: _ ->
            (* TODO: Soon, we will allow the final argument to be an identifier
               which represents the entire list. This would be written as
               `<tag>...list</tag>`. If you imagine there being an implicit []
               inside the tag, then it would be consistent with array spread:
               [...list] evaluates to the thing as list. *)
            let hasLabelledChildrenLiteral =
              List.exists
                (function Labelled "children", _ -> true | _ -> false)
                l
            in
            let rec hasSingleNonLabelledUnitAndIsAtTheEnd l =
              match l with
              | [] -> false
              | ( Nolabel
                , { pexp_desc = Pexp_construct ({ txt = Lident "()"; _ }, _)
                  ; _
                  } )
                :: [] ->
                true
              | (Nolabel, _) :: _ -> false
              | _ :: rest -> hasSingleNonLabelledUnitAndIsAtTheEnd rest
            in
            if
              hasLabelledChildrenLiteral
              && hasSingleNonLabelledUnitAndIsAtTheEnd l
            then
              match loc.txt with
              | Ldot (moduleLid, "createElement") ->
                Some
                  (self#formatJSXComponent
                     (String.concat "." (Longident.flatten_exn moduleLid))
                     l)
              | lid ->
                Some
                  (self#formatJSXComponent
                     (String.concat "." (Longident.flatten_exn lid))
                     l)
            else None
          | ( Pexp_apply
                ( { pexp_desc =
                      Pexp_letmodule
                        ( _
                        , ({ pmod_desc = Pmod_apply _; _ } as app)
                        , { pexp_desc = Pexp_ident loc; _ } )
                  ; _
                  }
                , l )
            , []
            , _jsx :: _ ) ->
            (* TODO: Soon, we will allow the final argument to be an identifier
               which represents the entire list. This would be written as
               `<tag>...list</tag>`. If you imagine there being an implicit []
               inside the tag, then it would be consistent with array spread:
               [...list] evaluates to the thing as list. *)
            let rec extract_apps args = function
              | { pmod_desc = Pmod_apply (m1, { pmod_desc = Pmod_ident loc; _ })
                ; _
                } ->
                let arg = String.concat "." (Longident.flatten_exn loc.txt) in
                extract_apps (arg :: args) m1
              | { pmod_desc = Pmod_ident loc; _ } ->
                String.concat "." (Longident.flatten_exn loc.txt) :: args
              | _ ->
                failwith
                  "Functors in JSX tags support only module names as parameters"
            in
            let hasLabelledChildrenLiteral =
              List.exists
                (function Labelled "children", _ -> true | _ -> false)
                l
            in
            let rec hasSingleNonLabelledUnitAndIsAtTheEnd l =
              match l with
              | [] -> false
              | ( Nolabel
                , { pexp_desc = Pexp_construct ({ txt = Lident "()"; _ }, _)
                  ; _
                  } )
                :: [] ->
                true
              | (Nolabel, _) :: _ -> false
              | _ :: rest -> hasSingleNonLabelledUnitAndIsAtTheEnd rest
            in
            if
              hasLabelledChildrenLiteral
              && hasSingleNonLabelledUnitAndIsAtTheEnd l
            then
              match Longident.flatten_exn loc.txt with
              | [] | [ _ ] ->
                Some (self#formatJSXComponent (Longident.last_exn loc.txt) l)
              | _ ->
                if Longident.last_exn loc.txt = "createElement"
                then
                  match extract_apps [] app with
                  | ftor :: args ->
                    let applied = ftor ^ "(" ^ String.concat ", " args ^ ")" in
                    Some
                      (self#formatJSXComponent
                         ~closeComponentName:ftor
                         applied
                         l)
                  | _ -> None
                else None
            else None
          | _ -> None

        method sugar_set_expr_parts e =
          if e.pexp_attributes != []
          then None (* should also check attributes underneath *)
          else
            match e.pexp_desc with
            | Pexp_apply
                ( { pexp_desc =
                      Pexp_ident { txt = Ldot (Lident "Array", "set"); _ }
                  ; _
                  }
                , [ (_, e1); (_, e2); (_, e3) ] ) ->
              let prec = Custom "prec_lbracket" in
              let lhs =
                self#unparseResolvedRule
                  (self#ensureExpression ~reducesOnToken:prec e1)
              in
              Some (self#access "[" "]" lhs (self#unparseExpr e2), e3)
            | Pexp_apply
                ( { pexp_desc =
                      Pexp_ident { txt = Ldot (Lident "String", "set"); _ }
                  ; _
                  }
                , [ (_, e1); (_, e2); (_, e3) ] ) ->
              let prec = Custom "prec_lbracket" in
              let lhs =
                self#unparseResolvedRule
                  (self#ensureExpression ~reducesOnToken:prec e1)
              in
              Some (self#access ".[" "]" lhs (self#unparseExpr e2), e3)
            | Pexp_apply
                ( { pexp_desc =
                      Pexp_ident
                        { txt = Ldot (Ldot (Lident "Bigarray", array), "set")
                        ; _
                        }
                  ; _
                  }
                , label_exprs ) ->
              (match array with
              | "Genarray" ->
                (match label_exprs with
                | [ (_, a); (_, { pexp_desc = Pexp_array ls; _ }); (_, c) ] ->
                  let formattedList = List.map self#unparseExpr ls in
                  let lhs =
                    makeList
                      [ self#simple_enough_to_be_lhs_dot_send a; atom "." ]
                  in
                  let rhs =
                    makeList
                      ~break:IfNeed
                      ~postSpace:true
                      ~sep:commaSep
                      ~wrap:("{", "}")
                      formattedList
                  in
                  Some (label lhs rhs, c)
                | _ -> None)
              | "Array1" | "Array2" | "Array3" ->
                (match label_exprs with
                | (_, a) :: rest ->
                  (match List.rev rest with
                  | (_, v) :: rest ->
                    let args = List.map snd (List.rev rest) in
                    let formattedList = List.map self#unparseExpr args in
                    let lhs =
                      makeList
                        [ self#simple_enough_to_be_lhs_dot_send a; atom "." ]
                    in
                    let rhs =
                      makeList
                        ~break:IfNeed
                        ~postSpace:true
                        ~sep:commaSep
                        ~wrap:("{", "}")
                        formattedList
                    in
                    Some (label lhs rhs, v)
                  | _ -> assert false)
                | _ -> assert false)
              | _ -> None)
            | _ -> None
        (** Detects "sugar expressions" (sugar for array/string setters) and
            returns their separate parts. *)

        (* How would we know not to print the sequence without { }; protecting the let a?
         *
         *                        let a
         *                         |
         *                       sequence
         *                      /        \
         *                let a           print a
         *                alert a
         * let res = {
         *   let a = something();
         *   {                     \
         *     alert(a);           | portion to be parsed as a sequence()
         *     let a = 20;         | The final ; print(a) causes the entire
         *     alert(a);           | portion to be parsed as a sequence()
         *   };                    |
         *   print (a);            /
         * }
         *
         * ******************************************************************
         * Any time the First expression of a sequence is another sequence, or (as in
         * this case) a let, wrapping the first sequence expression in { } is
         * required.
         * ******************************************************************
        *)

        (** TODO: Configure the optional ability to print the *minimum* number
            of parens. It's simply a matter of changing [higherPrecedenceThan]
            to [higherOrEqualPrecedenceThan]. *)

        (* The point of the function is to ensure that
           ~reducesAfterRight:rightExpr will reduce at the proper time when it
           is reparsed, possibly wrapping it in parenthesis if needed. It
           ensures a rule doesn't reduce until *after* `reducesAfterRight` gets
           a chance to reduce. Example: The addition rule which has precedence
           of rightmost token "+", in `x + a * b` should not reduce until after
           the a * b gets a chance to reduce. This function would determine the
           minimum parens to ensure that. *)
        method ensureContainingRule ~withPrecedence ~reducesAfterRight () =
          match self#unparseExprRecurse reducesAfterRight with
          | SpecificInfixPrecedence ({ shiftPrecedence; _ }, rightRecurse) ->
            if higherPrecedenceThan shiftPrecedence withPrecedence
            then rightRecurse
            else if higherPrecedenceThan withPrecedence shiftPrecedence
            then
              LayoutNode
                (formatPrecedence
                   ~loc:reducesAfterRight.pexp_loc
                   (self#unparseResolvedRule rightRecurse))
            else if isRightAssociative ~prec:withPrecedence
            then rightRecurse
            else
              LayoutNode
                (formatPrecedence
                   ~loc:reducesAfterRight.pexp_loc
                   (self#unparseResolvedRule rightRecurse))
          | FunctionApplication itms ->
            let funApplExpr =
              formatAttachmentApplication
                applicationFinalWrapping
                None
                (itms, Some reducesAfterRight.pexp_loc)
            in
            (* Little hack: need to print parens for the `bar` application in
               e.g. `foo->other##(bar(baz))` or `foo->other->(bar(baz))`. *)
            if higherPrecedenceThan withPrecedence (Custom "prec_functionAppl")
            then
              LayoutNode
                (formatPrecedence ~loc:reducesAfterRight.pexp_loc funApplExpr)
            else LayoutNode funApplExpr
          | PotentiallyLowPrecedence itm ->
            LayoutNode (formatPrecedence ~loc:reducesAfterRight.pexp_loc itm)
          | Simple itm -> LayoutNode itm

        method ensureExpression ~reducesOnToken expr =
          match self#unparseExprRecurse expr with
          | SpecificInfixPrecedence ({ reducePrecedence; _ }, leftRecurse) ->
            if higherPrecedenceThan reducePrecedence reducesOnToken
            then leftRecurse
            else if higherPrecedenceThan reducesOnToken reducePrecedence
            then
              LayoutNode
                (formatPrecedence
                   ~loc:expr.pexp_loc
                   (self#unparseResolvedRule leftRecurse))
            else if isLeftAssociative ~prec:reducesOnToken
            then leftRecurse
            else
              LayoutNode
                (formatPrecedence
                   ~loc:expr.pexp_loc
                   (self#unparseResolvedRule leftRecurse))
          | FunctionApplication itms ->
            LayoutNode
              (formatAttachmentApplication
                 applicationFinalWrapping
                 None
                 (itms, Some expr.pexp_loc))
          | PotentiallyLowPrecedence itm ->
            LayoutNode (formatPrecedence ~loc:expr.pexp_loc itm)
          | Simple itm -> LayoutNode itm

        method unparseExpr x =
          match self#unparseExprRecurse x with
          | SpecificInfixPrecedence (_, resolvedRule) ->
            self#unparseResolvedRule resolvedRule
          | FunctionApplication itms ->
            formatAttachmentApplication
              applicationFinalWrapping
              None
              (itms, Some x.pexp_loc)
          | PotentiallyLowPrecedence itm -> itm
          | Simple itm -> itm
        (** Attempts to unparse: The beginning of a more general printing
            algorithm, that determines how to print based on precedence of
            tokens and rules. The end goal is that this should be completely
            auto-generated from the Menhir parsing tables. We could move more
            and more into this function.

            You could always just call self#expression, but `unparseExpr` will
            render infix/prefix/unary/terary fixities in their beautiful forms
            while minimizing parenthesis. *)

        (* This method may not even be needed *)
        method unparseUnattributedExpr x =
          match Reason_attributes.partitionAttributes x.pexp_attributes with
          | { docAttrs = []; stdAttrs = []; _ } -> self#unparseExpr x
          | _ -> makeList ~wrap:("(", ")") [ self#unparseExpr x ]

        (* ensureExpr ensures that the expression is wrapped in parens
         * e.g. is necessary in cases like:
         * let display = (:message=("hello": string)) => 1;
         * but not in cases like:
         * let f = (a: bool) => 1;
         * TODO: in the future we should probably use the type ruleCategory
         * to 'automatically' ensure the validity of a constraint expr with parens...
        *)
        method unparseProtectedExpr ?(forceParens = false) e =
          let itm =
            match e with
            | { pexp_attributes = []; pexp_desc = Pexp_constraint (x, ct); _ }
              ->
              let x = self#unparseExpr x in
              let children =
                [ x; label ~space:true (atom ":") (self#core_type ct) ]
              in
              if forceParens
              then makeList ~wrap:("(", ")") children
              else makeList children
            | { pexp_attributes; pexp_desc = Pexp_constant c; _ } ->
              (* When we have Some(-1) or someFunction(-1, -2), the arguments -1 and -2
               * pass through this case. In this context they don't need to be wrapped in extra parens
               * Some((-1)) should be printed as Some(-1). This is in contrast with
               * 1 + (-1) where we print the parens for readability. *)
              let raw_literal, pexp_attributes =
                Reason_attributes.extract_raw_literal pexp_attributes
              in
              let constant = self#constant ?raw_literal ~parens:forceParens c in
              (match pexp_attributes with
              | [] -> constant
              | attrs ->
                let formattedAttrs =
                  makeSpacedBreakableInlineList
                    (List.map self#item_attribute attrs)
                in
                makeSpacedBreakableInlineList [ formattedAttrs; constant ])
            | { pexp_desc = Pexp_fun _; _ } -> self#formatPexpFun e
            | x -> self#unparseExpr x
          in
          source_map ~loc:e.pexp_loc itm

        method simplifyUnparseExpr
          ?(inline = false)
          ?(even_wrap_simple = false)
          ?(wrap = "(", ")")
          x =
          match self#unparseExprRecurse x, even_wrap_simple with
          | SpecificInfixPrecedence (_, itm), _ ->
            formatPrecedence
              ~inline
              ~wrap
              ~loc:x.pexp_loc
              (self#unparseResolvedRule itm)
          | FunctionApplication itms, _ ->
            formatPrecedence
              ~inline
              ~wrap
              ~loc:x.pexp_loc
              (formatAttachmentApplication
                 applicationFinalWrapping
                 None
                 (itms, Some x.pexp_loc))
          | PotentiallyLowPrecedence itm, _ | Simple itm, true ->
            formatPrecedence ~inline ~wrap ~loc:x.pexp_loc itm
          | Simple itm, false -> itm

        method unparseResolvedRule =
          function
          | LayoutNode layoutNode -> layoutNode
          | InfixTree _ as infixTree ->
            formatComputedInfixChain (computeInfixChain infixTree)

        method unparseExprApplicationItems x =
          match self#unparseExprRecurse x with
          | SpecificInfixPrecedence (_, wrappedRule) ->
            let itm = self#unparseResolvedRule wrappedRule in
            [ itm ], Some x.pexp_loc
          | FunctionApplication itms -> itms, Some x.pexp_loc
          | PotentiallyLowPrecedence itm -> [ itm ], Some x.pexp_loc
          | Simple itm -> [ itm ], Some x.pexp_loc

        (* Provides beautiful printing for pipe first sugar:
         * foo
         * ->f(a, b)
         * ->g(c, d)
        *)
        method formatPipeFirst e =
          let module PipeFirstTree = struct
            type exp = Parsetree.expression

            type flatNode =
              | Exp of exp
              | ExpU of exp (* uncurried *)
              | Args of (Asttypes.arg_label * exp) list

            type flatT = flatNode list

            type node =
              { exp : exp
              ; args : (Asttypes.arg_label * exp) list
              ; uncurried : bool
              }

            type t = node list

            let formatNode ?prefix ?(first = false) { exp; args; uncurried } =
              let formatLayout expr =
                let formatted =
                  if first
                  then
                    self#ensureExpression
                      ~reducesOnToken:(Token pipeFirstToken)
                      expr
                  else
                    match expr with
                    (* a->foo(x, _) and a->(foo(x, _)) are equivalent under pipe first
                     * (a->foo)(x, _) is unnatural and desugars to
                     *    (__x) => (a |. foo)(x, __x)
                     * Under `->`, it makes more sense to desugar into
                     *  a |. (__x => foo(x, __x))
                     *
                     * Hence we don't need parens in this case.
                    *)
                    | expr when Reason_heuristics.isUnderscoreApplication expr
                      ->
                      LayoutNode (self#unparseExpr expr)
                    | _ ->
                      self#ensureContainingRule
                        ~withPrecedence:(Token pipeFirstToken)
                        ~reducesAfterRight:expr
                        ()
                in
                self#unparseResolvedRule formatted
              in
              let parens =
                match exp.pexp_desc with
                | Pexp_apply (e, _) ->
                  printedStringAndFixityExpr e = UnaryPostfix "^"
                | _ -> false
              in
              let layout =
                match args with
                | [] ->
                  let e = formatLayout exp in
                  (match prefix with Some l -> makeList [ l; e ] | None -> e)
                | args ->
                  let args =
                    List.map
                      (fun (label, arg) ->
                         label, self#process_underscore_application arg)
                      args
                  in
                  let fakeApplExp =
                    let loc_end =
                      match List.rev args with
                      | (_, e) :: _ -> e.pexp_loc.loc_end
                      | _ -> exp.pexp_loc.loc_end
                    in
                    { exp with pexp_loc = { exp.pexp_loc with loc_end } }
                  in
                  makeList
                    (self#formatFunAppl
                       ?prefix
                       ~jsxAttrs:[]
                       ~args
                       ~funExpr:exp
                       ~applicationExpr:fakeApplExp
                       ~uncurried
                       ())
              in
              if parens then formatPrecedence layout else layout
          end
          in
          (* Imagine: foo->f(a, b)->g(c,d)
           * The corresponding parsetree looks more like:
           *   (((foo->f)(a,b))->g)(c, d)
           * The extra Pexp_apply nodes, e.g. (foo->f), result into a
           * nested/recursive ast which is pretty inconvenient in terms of printing.
           * For printing purposes we actually want something more like:
           *  foo->|f(a,b)|->|g(c, d)|
           * in order to provide to following printing:
           *  foo
           *  ->f(a, b)
           *  ->g(c, d)
           * The job of "flatten" is to turn the inconvenient, nested ast
           *  (((foo->f)(a,b))->g)(c, d)
           * into
           *  [Exp foo; Exp f; Args [a; b]; Exp g; Args [c; d]]
           * which can be processed for printing purposes.
          *)
          let rec flatten ?(uncurried = false) acc = function
            | { pexp_desc =
                  Pexp_apply
                    ( { pexp_desc = Pexp_ident { txt = Longident.Lident "|."; _ }
                      ; _
                      }
                    , [ (Nolabel, arg1); (Nolabel, arg2) ] )
              ; _
              } ->
              flatten (PipeFirstTree.Exp arg2 :: acc) arg1
            | { pexp_attributes
              ; pexp_desc =
                  Pexp_apply
                    ( { pexp_desc =
                          Pexp_apply
                            ( { pexp_desc =
                                  Pexp_ident { txt = Longident.Lident "|."; _ }
                              ; _
                              }
                            , [ (Nolabel, arg1); (Nolabel, arg2) ] )
                      ; _
                      }
                    , args )
              ; _
              } as e ->
              let args = PipeFirstTree.Args args in
              (match pexp_attributes with
              | [ { attr_name = { txt = "u" | "bs"; _ }
                  ; attr_payload = PStr []
                  ; _
                  }
                ] ->
                flatten (PipeFirstTree.ExpU arg2 :: args :: acc) arg1
              | [] ->
                (* the uncurried attribute might sit on the Pstr_eval
                 * enclosing the Pexp_apply*)
                if uncurried
                then flatten (PipeFirstTree.ExpU arg2 :: args :: acc) arg1
                else flatten (PipeFirstTree.Exp arg2 :: args :: acc) arg1
              | _ -> PipeFirstTree.Exp e :: acc)
            | { pexp_desc = Pexp_ident { txt = Longident.Lident "|."; _ }; _ }
              ->
              acc
            | arg -> PipeFirstTree.Exp arg :: acc
          in
          (* Given: foo->f(a, b)->g(c, d)
           * We get the following PipeFirstTree.flatNode list:
           *   [Exp foo; Exp f; Args [a; b]; Exp g; Args [c; d]]
           * The job of `parse` is to turn the "flat representation"
           * (a.k.a. PipeFirstTree.flastNode list) into a more convenient structure
           * that allows us to express the segments: "foo" "f(a, b)" "g(c, d)".
           * PipeFirstTree.t expresses those segments.
           *  [{exp = foo; args = []}; {exp = f; args = [a; b]}; {exp = g; args = [c; d]}]
          *)
          let rec parse acc = function
            | PipeFirstTree.Exp e :: PipeFirstTree.Args args :: xs ->
              parse
                (PipeFirstTree.{ exp = e; args; uncurried = false } :: acc)
                xs
            | PipeFirstTree.ExpU e :: PipeFirstTree.Args args :: xs ->
              parse
                (PipeFirstTree.{ exp = e; args; uncurried = true } :: acc)
                xs
            | PipeFirstTree.Exp e :: xs ->
              parse
                (PipeFirstTree.{ exp = e; args = []; uncurried = false } :: acc)
                xs
            | _ -> List.rev acc
          in
          (* Given: foo->f(. a,b);
           * The uncurried attribute doesn't sit on the Pexp_apply, but sits on
           * the top level Pstr_eval. We don't have access to top-level context here,
           * hence the lookup in the global uncurriedTable to correctly determine
           * if we need to print uncurried. *)
          let uncurried =
            try Hashtbl.find uncurriedTable e.pexp_loc with Not_found -> false
          in
          (* Turn
           *  foo->f(a, b)->g(c, d)
           * into
           *  [Exp foo; Exp f; Args [a; b]; Exp g; Args [c; d]]
          *)
          let (flatNodes : PipeFirstTree.flatT) = flatten ~uncurried [] e in
          (* Turn
           *  [Exp foo; Exp f; Args [a; b]; Exp g; Args [c; d]]
           * into
           *  [{exp = foo; args = []}; {exp = f; args = [a; b]}; {exp = g; args = [c; d]}]
          *)
          let (pipetree : PipeFirstTree.t) = parse [] flatNodes in
          (* Turn
           *  [{exp = foo; args = []}; {exp = f; args = [a; b]}; {exp = g; args = [c; d]}]
           * into
           *  [foo; ->f(a, b); ->g(c, d)]
          *)
          let pipeSegments =
            match pipetree with
            (* Special case printing of
             * foo->bar(
             *  aa,
             *  bb,
             * )
             *
             *  We don't want
             *  foo
             *  ->bar(
             *      aa,
             *      bb
             *    )
             *
             *  Notice how `foo->bar` shouldn't break, it wastes space and is
             *  inconsistent with
             *  foo.bar(
             *    aa,
             *    bb,
             *  )
            *)
            | [ ({ exp = { pexp_desc = Pexp_ident _; _ }; _ } as hd); last ] ->
              let prefix =
                Some
                  (makeList
                     [ PipeFirstTree.formatNode ~first:true hd; atom "->" ])
              in
              [ PipeFirstTree.formatNode ?prefix last ]
            | hd :: tl ->
              let hd = PipeFirstTree.formatNode ~first:true hd in
              let tl =
                List.map
                  (fun node ->
                     makeList [ atom "->"; PipeFirstTree.formatNode node ])
                  tl
              in
              hd :: tl
            | [] -> []
          in
          (* Provide nice breaking for: [foo; ->f(a, b); ->g(c, d)]
           * foo
           * ->f(a, b)
           * ->g(c, d)
          *)
          makeList ~break:IfNeed ~inline:(true, true) pipeSegments

        (*
           * Replace (__x) => foo(__x) with foo(_)
        *)
        method process_underscore_application x =
          let process_application expr =
            let process_arg (l, e) =
              match e.pexp_desc with
              | Pexp_ident ({ txt = Lident "__x"; _ } as id) ->
                let pexp_desc = Pexp_ident { id with txt = Lident "_" } in
                l, { e with pexp_desc }
              | _ -> l, e
            in
            match expr.pexp_desc with
            | Pexp_apply (e_fun, args) ->
              let pexp_desc = Pexp_apply (e_fun, List.map process_arg args) in
              { expr with pexp_desc }
            | _ -> expr
          in
          match x.pexp_desc with
          | Pexp_fun
              ( Nolabel
              , None
              , { ppat_desc = Ppat_var { txt = "__x"; _ }; _ }
              , ({ pexp_desc = Pexp_apply _; _ } as e) ) ->
            process_application e
          | Pexp_fun (l, eo, p, e) ->
            let e_processed = self#process_underscore_application e in
            if e == e_processed
            then x
            else { x with pexp_desc = Pexp_fun (l, eo, p, e_processed) }
          | _ -> x

        method unparseExprRecurse x =
          let x = self#process_underscore_application x in

          (* If there are any attributes, render unary like `(~-) x [@ppx]`, and
             infix like `(+) x y [@attr]` *)
          let { Reason_attributes.arityAttrs
              ; stdAttrs
              ; jsxAttrs
              ; stylisticAttrs
              ; uncurried
              ; _
              }
            =
            Reason_attributes.partitionAttributes
              ~allowUncurry:(Reason_heuristics.bsExprCanBeUncurried x)
              x.pexp_attributes
          in
          let stylisticAttrs =
            Reason_attributes.maybe_remove_stylistic_attrs
              stylisticAttrs
              ~should_preserve:preserve_braces
          in
          let () =
            if uncurried then Hashtbl.add uncurriedTable x.pexp_loc true
          in
          let x =
            { x with
              pexp_attributes =
                stylisticAttrs @ arityAttrs @ stdAttrs @ jsxAttrs
            }
          in
          (* If there's any attributes, recurse without them, then apply them to
             the ends of functions, or simplify infix printings then append. *)
          match stdAttrs, x.pexp_desc with
          | _, Pexp_letop _ ->
            (* `Pexp_letop` is a bit different than `let` bindings because the
               attributes are in `Pexp_letop` rather than the `value_binding`
               type (check https://github.com/ocaml/ocaml/issues/9301 too), so
               we must treat it a bit differently if we want to print the
               attributes inside the braces. *)
            FunctionApplication [ makeLetSequence (self#letList x) ]
          | _ :: _, _ ->
            let withoutVisibleAttrs =
              { x with
                pexp_attributes = stylisticAttrs @ arityAttrs @ jsxAttrs
              }
            in
            let attributesAsList = List.map self#attribute stdAttrs in
            let itms =
              match self#unparseExprRecurse withoutVisibleAttrs with
              | SpecificInfixPrecedence ({ reducePrecedence; _ }, wrappedRule)
                ->
                let itm = self#unparseResolvedRule wrappedRule in
                (match reducePrecedence with
                (* doesn't need wrapping; we know how to parse *)
                | Custom "prec_lbracket" | Token "." -> [ itm ]
                | _ -> [ formatPrecedence ~loc:x.pexp_loc itm ])
              | FunctionApplication itms -> itms
              | PotentiallyLowPrecedence itm ->
                [ formatPrecedence ~loc:x.pexp_loc itm ]
              | Simple itm -> [ itm ]
            in
            FunctionApplication
              [ makeList
                  ~break:IfNeed
                  ~inline:(true, true)
                  ~indent:0
                  ~postSpace:true
                  (List.concat [ attributesAsList; itms ])
              ]
          | [], _ ->
            (match self#simplest_expression x with
            | Some se -> Simple se
            | None ->
              let self = self#reset_request_braces in
              (match x.pexp_desc with
              | Pexp_apply (e, ls) ->
                let ls =
                  List.map
                    (fun (l, expr) ->
                       l, self#process_underscore_application expr)
                    ls
                in
                (match e, ls with
                | e, _ when Reason_heuristics.isPipeFirst e ->
                  let prec = Token pipeFirstToken in
                  SpecificInfixPrecedence
                    ( { reducePrecedence = prec; shiftPrecedence = prec }
                    , LayoutNode (self#formatPipeFirst x) )
                | ( { pexp_desc =
                        Pexp_ident { txt = Ldot (Lident "Array", "get"); _ }
                    ; _
                    }
                  , [ (_, e1); (_, e2) ] ) ->
                  (match e1.pexp_desc with
                  | Pexp_ident { txt = Lident "_"; _ } ->
                    let k = atom "Array.get" in
                    let v =
                      makeList
                        ~postSpace:true
                        ~sep:(Layout.Sep ",")
                        ~wrap:("(", ")")
                        [ atom "_"; self#unparseExpr e2 ]
                    in
                    Simple (label k v)
                  | _ ->
                    let prec = Custom "prec_lbracket" in
                    let lhs =
                      self#unparseResolvedRule
                        (self#ensureExpression ~reducesOnToken:prec e1)
                    in
                    let rhs = self#unparseExpr e2 in
                    SpecificInfixPrecedence
                      ( { reducePrecedence = prec; shiftPrecedence = prec }
                      , LayoutNode (self#access "[" "]" lhs rhs) ))
                | ( { pexp_desc =
                        Pexp_ident { txt = Ldot (Lident "String", "get"); _ }
                    ; _
                    }
                  , [ (_, e1); (_, e2) ] ) ->
                  if Reason_heuristics.isUnderscoreIdent e1
                  then
                    let k = atom "String.get" in
                    let v =
                      makeList
                        ~postSpace:true
                        ~sep:(Layout.Sep ",")
                        ~wrap:("(", ")")
                        [ atom "_"; self#unparseExpr e2 ]
                    in
                    Simple (label k v)
                  else
                    let prec = Custom "prec_lbracket" in
                    let lhs =
                      self#unparseResolvedRule
                        (self#ensureExpression ~reducesOnToken:prec e1)
                    in
                    let rhs = self#unparseExpr e2 in
                    SpecificInfixPrecedence
                      ( { reducePrecedence = prec; shiftPrecedence = prec }
                      , LayoutNode (self#access ".[" "]" lhs rhs) )
                | ( { pexp_desc =
                        Pexp_ident
                          { txt =
                              Ldot (Ldot (Lident "Bigarray", "Genarray"), "get")
                          ; _
                          }
                    ; _
                    }
                  , [ (_, e1); (_, ({ pexp_desc = Pexp_array ls; _ } as e2)) ] )
                  ->
                  if Reason_heuristics.isUnderscoreIdent e1
                  then
                    let k = atom "Bigarray.Genarray.get" in
                    let v =
                      makeList
                        ~postSpace:true
                        ~sep:(Layout.Sep ",")
                        ~wrap:("(", ")")
                        [ atom "_"; self#unparseExpr e2 ]
                    in
                    Simple (label k v)
                  else
                    let formattedList = List.map self#unparseExpr ls in
                    let lhs =
                      makeList
                        [ self#simple_enough_to_be_lhs_dot_send e1; atom "." ]
                    in
                    let rhs =
                      makeList
                        ~break:IfNeed
                        ~postSpace:true
                        ~sep:commaSep
                        ~wrap:("{", "}")
                        formattedList
                    in
                    let prec = Custom "prec_lbracket" in
                    SpecificInfixPrecedence
                      ( { reducePrecedence = prec; shiftPrecedence = prec }
                      , LayoutNode (label lhs rhs) )
                | ( { pexp_desc =
                        Pexp_ident
                          { txt =
                              Ldot
                                ( Ldot
                                    ( Lident "Bigarray"
                                    , (("Array1" | "Array2" | "Array3") as
                                       arrayIdent) )
                                , "get" )
                          ; _
                          }
                    ; _
                    }
                  , (_, e1) :: rest ) ->
                  if Reason_heuristics.isUnderscoreIdent e1
                  then
                    let k = atom ("Bigarray." ^ arrayIdent ^ ".get") in
                    let v =
                      makeList
                        ~postSpace:true
                        ~sep:(Layout.Sep ",")
                        ~wrap:("(", ")")
                        (atom "_"
                        :: List.map (fun (_, e) -> self#unparseExpr e) rest)
                    in
                    Simple (label k v)
                  else
                    let formattedList =
                      List.map self#unparseExpr (List.map snd rest)
                    in
                    let lhs =
                      makeList
                        [ self#simple_enough_to_be_lhs_dot_send e1; atom "." ]
                    in
                    let rhs =
                      makeList
                        ~break:IfNeed
                        ~postSpace:true
                        ~sep:commaSep
                        ~wrap:("{", "}")
                        formattedList
                    in
                    let prec = Custom "prec_lbracket" in
                    SpecificInfixPrecedence
                      ( { reducePrecedence = prec; shiftPrecedence = prec }
                      , LayoutNode (label lhs rhs) )
                | _ ->
                  (match self#sugar_set_expr_parts x with
                  (* Returns None if there's attributes - would render as regular function *)
                  (* Format as if it were an infix function application with identifier "=" *)
                  | Some (simplyFormatedLeftItm, rightExpr) ->
                    let tokenPrec = Token updateToken in
                    let rightItm =
                      self#ensureContainingRule
                        ~withPrecedence:tokenPrec
                        ~reducesAfterRight:rightExpr
                        ()
                    in
                    let leftWithOp =
                      makeList
                        ~postSpace:true
                        [ simplyFormatedLeftItm; atom updateToken ]
                    in
                    let expr =
                      label
                        ~space:true
                        leftWithOp
                        (self#unparseResolvedRule rightItm)
                    in
                    SpecificInfixPrecedence
                      ( { reducePrecedence = tokenPrec
                        ; shiftPrecedence = tokenPrec
                        }
                      , LayoutNode expr )
                  | None ->
                    (match printedStringAndFixityExpr e, ls with
                    (* We must take care not to print two subsequent prefix
                       operators without spaces between them (`! !` could become
                       `!!` which is totally different). *)
                    | AlmostSimplePrefix prefixStr, [ (Nolabel, rightExpr) ] ->
                      let forceSpace =
                        match rightExpr.pexp_desc with
                        | Pexp_apply (ee, _) ->
                          (match printedStringAndFixityExpr ee with
                          | AlmostSimplePrefix _ -> true
                          | _ -> false)
                        | _ -> false
                      in
                      let prec = Token prefixStr in
                      let rightItm =
                        self#unparseResolvedRule
                          (self#ensureContainingRule
                             ~withPrecedence:prec
                             ~reducesAfterRight:rightExpr
                             ())
                      in
                      SpecificInfixPrecedence
                        ( { reducePrecedence = prec; shiftPrecedence = prec }
                        , LayoutNode
                            (label ~space:forceSpace (atom prefixStr) rightItm)
                        )
                    | UnaryPostfix postfixStr, [ (Nolabel, leftExpr) ] ->
                      let forceSpace =
                        match leftExpr.pexp_desc with
                        | Pexp_apply (ee, _) ->
                          (match printedStringAndFixityExpr ee with
                          | UnaryPostfix "^" | AlmostSimplePrefix _ -> true
                          | _ -> false)
                        | _ -> false
                      in
                      let leftItm =
                        match leftExpr.pexp_desc with
                        | Pexp_apply (e, _) ->
                          (match printedStringAndFixityExpr e with
                          | Infix printedIdent
                            when requireNoSpaceFor printedIdent
                                 || Reason_heuristics.isPipeFirst e ->
                            self#unparseExpr leftExpr
                          | _ -> self#simplifyUnparseExpr leftExpr)
                        | Pexp_field _ -> self#unparseExpr leftExpr
                        | _ -> self#simplifyUnparseExpr leftExpr
                      in
                      Simple (label ~space:forceSpace leftItm (atom postfixStr))
                    | ( Infix printedIdent
                      , [ (Nolabel, leftExpr); (Nolabel, rightExpr) ] ) ->
                      let infixToken = Token printedIdent in
                      let rightItm =
                        self#ensureContainingRule
                          ~withPrecedence:infixToken
                          ~reducesAfterRight:rightExpr
                          ()
                      in
                      let leftItm =
                        self#ensureExpression
                          ~reducesOnToken:infixToken
                          leftExpr
                      in
                      (* Left exprs of infix tokens which we don't print spaces
                         for (e.g. `##`) need to be wrapped in parens in the
                         case of postfix `^`. Otherwise, printing will be
                         ambiguous as `^` is also a valid start of an infix
                         operator. *)
                      let formattedLeftItm =
                        match leftItm with
                        | LayoutNode x ->
                          (match leftExpr.pexp_desc with
                          | Pexp_apply (e, _) ->
                            (match printedStringAndFixityExpr e with
                            | UnaryPostfix "^"
                              when requireNoSpaceFor printedIdent ->
                              LayoutNode
                                (formatPrecedence ~loc:leftExpr.pexp_loc x)
                            | _ -> leftItm)
                          | _ -> leftItm)
                        | InfixTree _ -> leftItm
                      in
                      let infixTree =
                        InfixTree (printedIdent, formattedLeftItm, rightItm)
                      in
                      SpecificInfixPrecedence
                        ( { reducePrecedence = infixToken
                          ; shiftPrecedence = infixToken
                          }
                        , infixTree )
                    (* Will be rendered as `(+) a b c` which is parsed with
                       higher precedence than all the other forms unparsed
                       here.*)
                    | UnaryPlusPrefix printedIdent, [ (Nolabel, rightExpr) ] ->
                      let prec = Custom "prec_unary" in
                      let rightItm =
                        self#unparseResolvedRule
                          (self#ensureContainingRule
                             ~withPrecedence:prec
                             ~reducesAfterRight:rightExpr
                             ())
                      in
                      let expr =
                        label ~space:true (atom printedIdent) rightItm
                      in
                      SpecificInfixPrecedence
                        ( { reducePrecedence = prec
                          ; shiftPrecedence = Token printedIdent
                          }
                        , LayoutNode expr )
                    | ( (UnaryMinusPrefix printedIdent as x)
                      , [ (Nolabel, rightExpr) ] )
                    | ( (UnaryNotPrefix printedIdent as x)
                      , [ (Nolabel, rightExpr) ] ) ->
                      let forceSpace =
                        match x with
                        | UnaryMinusPrefix _ -> true
                        | _ ->
                          (match rightExpr.pexp_desc with
                          | Pexp_apply
                              ( { pexp_desc = Pexp_ident { txt = Lident s; _ }
                                ; _
                                }
                              , _ ) ->
                            isSimplePrefixToken s
                          | _ -> false)
                      in
                      let prec = Custom "prec_unary" in
                      let rightItm =
                        self#unparseResolvedRule
                          (self#ensureContainingRule
                             ~withPrecedence:prec
                             ~reducesAfterRight:rightExpr
                             ())
                      in
                      let expr =
                        label ~space:forceSpace (atom printedIdent) rightItm
                      in
                      SpecificInfixPrecedence
                        ( { reducePrecedence = prec
                          ; shiftPrecedence = Token printedIdent
                          }
                        , LayoutNode expr )
                    (* Will need to be rendered in self#expression as (~-) x y
                       z. *)
                    | _, _ ->
                      (* This case will happen when there is something like
                       *
                       *   Bar.createElement a::1 b::2 [] [@bla] [@JSX]
                       *
                       * At this point the bla will be stripped (because it's a visible
                       * attribute) but the JSX will still be there.
                      *)

                      (* this case also happens when we have something like:
                       * List.map((a) => a + 1, numbers);
                       * We got two "List.map" as Pexp_ident & a list of arguments:
                       * [`(a) => a + 1`; `numbers`]
                       *
                       * Another possible case is:
                       * describe("App", () =>
                       *   test("math", () =>
                       *     Expect.expect(1 + 2) |> toBe(3)));
                      *)
                      let uncurried =
                        try Hashtbl.find uncurriedTable x.pexp_loc with
                        | Not_found -> false
                      in
                      FunctionApplication
                        (self#formatFunAppl
                           ~uncurried
                           ~jsxAttrs
                           ~args:ls
                           ~applicationExpr:x
                           ~funExpr:e
                           ()))))
              | Pexp_field (e, li) ->
                let prec = Token "." in
                let leftItm =
                  self#unparseResolvedRule
                    (self#ensureExpression ~reducesOnToken:prec e)
                in
                let { Reason_attributes.stdAttrs; _ } =
                  Reason_attributes.partitionAttributes e.pexp_attributes
                in
                let formattedLeftItm =
                  if stdAttrs == []
                  then leftItm
                  else formatPrecedence ~loc:e.pexp_loc leftItm
                in
                let layout =
                  label
                    (makeList [ formattedLeftItm; atom "." ])
                    (self#longident_loc li)
                in
                SpecificInfixPrecedence
                  ( { reducePrecedence = prec; shiftPrecedence = prec }
                  , LayoutNode layout )
              | Pexp_construct (li, Some eo)
                when not (is_simple_construct (view_expr x)) ->
                (match view_expr x with
                (* TODO: Explicit arity *)
                | `normal ->
                  let arityIsClear = isArityClear arityAttrs in
                  FunctionApplication
                    [ self#constructor_expression
                        ~arityIsClear
                        stdAttrs
                        (self#longident_loc li)
                        eo
                    ]
                | _ -> assert false)
              | Pexp_variant (l, Some eo) ->
                if arityAttrs != []
                then
                  raise
                    (NotPossible
                       "Should never see embedded attributes on poly variant")
                else
                  FunctionApplication
                    [ self#constructor_expression
                        ~polyVariant:true
                        ~arityIsClear:true
                        stdAttrs
                        (atom ("`" ^ l))
                        eo
                    ]
              (* TODO: Should protect this identifier *)
              | Pexp_setinstvar (s, rightExpr) ->
                let rightItm =
                  self#unparseResolvedRule
                    (self#ensureContainingRule
                       ~withPrecedence:(Token updateToken)
                       ~reducesAfterRight:rightExpr
                       ())
                in
                let expr =
                  label
                    ~space:true
                    (makeList
                       ~postSpace:true
                       [ protectIdentifier s.txt; atom updateToken ])
                    rightItm
                in
                SpecificInfixPrecedence
                  ( { reducePrecedence = Token updateToken
                    ; shiftPrecedence = Token updateToken
                    }
                  , LayoutNode expr )
              | Pexp_setfield (leftExpr, li, rightExpr) ->
                let rightItm =
                  self#unparseResolvedRule
                    (self#ensureContainingRule
                       ~withPrecedence:(Token updateToken)
                       ~reducesAfterRight:rightExpr
                       ())
                in
                let leftItm =
                  self#unparseResolvedRule
                    (self#ensureExpression ~reducesOnToken:(Token ".") leftExpr)
                in
                let leftLbl =
                  label (makeList [ leftItm; atom "." ]) (self#longident_loc li)
                in
                let expr =
                  label
                    ~space:true
                    (makeList ~postSpace:true [ leftLbl; atom updateToken ])
                    rightItm
                in
                SpecificInfixPrecedence
                  ( { reducePrecedence = Token updateToken
                    ; shiftPrecedence = Token updateToken
                    }
                  , LayoutNode expr )
              | Pexp_match (e, l) when detectTernary l != None ->
                (match detectTernary l with
                | None -> raise (Invalid_argument "Impossible")
                | Some (tt, ff) ->
                  let ifTrue = self#reset_request_braces#unparseExpr tt in
                  let testItem =
                    self#unparseResolvedRule
                      (self#reset_request_braces#ensureExpression
                         e
                         ~reducesOnToken:(Token "?"))
                  in
                  let ifFalse =
                    self#unparseResolvedRule
                      (self#reset_request_braces#ensureContainingRule
                         ~withPrecedence:(Token ":")
                         ~reducesAfterRight:ff
                         ())
                  in
                  let trueBranch =
                    label ~space:true ~break:`Never (atom "?") ifTrue
                  in
                  let falseBranch =
                    label ~space:true ~break:`Never (atom ":") ifFalse
                  in
                  let expr =
                    label
                      ~space:true
                      testItem
                      (makeList
                         ~break:IfNeed
                         ~sep:(Sep " ")
                         ~inline:(true, true)
                         [ trueBranch; falseBranch ])
                  in
                  SpecificInfixPrecedence
                    ( { reducePrecedence = Token ":"
                      ; shiftPrecedence = Token "?"
                      }
                    , LayoutNode expr ))
              | _ ->
                (match self#expression_requiring_parens_in_infix x with
                | Some e -> e
                | None ->
                  raise (Invalid_argument "No match for unparsing expression"))))

        method formatNonSequencyExpression ?parent e =
          (* Instead of printing:
           *   let result =  { open Fmt; strf(foo);}
           *
           * We format as:
           *   let result = Fmt.(strf(foo))
           *
           * (Also see https://github.com/facebook/Reason/issues/114)
          *)
          match e.pexp_attributes, e.pexp_desc with
          | [], Pexp_record _ (* syntax sugar for M.{x:1} *)
          | [], Pexp_tuple _ (* syntax sugar for M.(a, b) *)
          | [], Pexp_object { pcstr_fields = []; _ } (* syntax sugar for M.{} *)
          | [], Pexp_construct ({ txt = Lident "::"; _ }, Some _)
          | [], Pexp_construct ({ txt = Lident "[]"; _ }, _)
          | [], Pexp_extension ({ txt = "mel.obj"; _ }, _) ->
            self#simplifyUnparseExpr e (* syntax sugar for M.[x,y] *)
          (* syntax sugar for the rest, wrap with parens to avoid ambiguity.
           * E.g., avoid M.(M2.v) being printed as M.M2.v
           * Or ReasonReact.(<> {string("Test")} </>);
          *)
          | _ ->
            (match parent with
            | Some parent
              when Reason_attributes.has_open_notation_attr
                     parent.pexp_attributes ->
              makeList
                ~break:IfNeed
                ~inline:(true, false)
                ~postSpace:true
                ~wrap:("(", ")")
                ~sep:(SepFinal (";", ""))
                (self#letList e)
            | Some _ | None ->
              makeList ~wrap:("(", ")") ~break:IfNeed [ self#unparseExpr e ])

        (* It's not enough to only check if precedence of an infix left/right is
         * greater than the infix itself. We also should likely pay attention to
         * left/right associativity. So how do we render the minimum number of
         * parenthesis?
         *
         * The intuition is that sequential right associative operators will
         * naturally build up deep trees on the right side (left builds up left-deep
         * trees). So by default, we add parens to model the tree structure that
         * we're rendering except when the parser will *naturally* parse the tree
         * structure that the parens assert.
         *
         * Sequential identical infix operators:
         * ------------------------------------
         * So if we see a nested infix operator of precedence Y, as one side of
         * another infix operator that has the same precedence (Y), that is S
         * associative on the S side of the function application, we don't need to
         * wrap in parens. In more detail:
         *
         * -Add parens around infix binary function application
         *   Exception 1: Unless we are a left-assoc operator of precedence X in the left branch of an operator w/ precedence X.
         *   Exception 2: Unless we are a right-assoc operator of precedence X in the right branch of an operator w/ precedence X.
         *   Exception 3: Unless we are a _any_-assoc X operator in the _any_ branch of an Y operator where X has greater precedence than Y.
         *
         * Note that the exceptions do not specify any special cases for mixing
         * left/right associativity. Precedence is what determines necessity of
         * parens for operators with non-identical precedences. Associativity
         * only determines necessity of parens for identically precedented operators.
         *
         * PLUS is left assoc:
         * - So this one *shouldn't* expand into two consecutive infix +:
         *
         *
         *        [Pexp_apply]
         *          /      \
         *     first +   [Pexp_apply]
         *                  /   \
         *              second + third
         *
         *
         * - This one *should*:
         *
         *                [Pexp_apply]
         *                  /      \
         *       [  Pexp_apply  ] + third
         *          /     \
         *       first +  second
         *
         *
         * COLONCOLON is right assoc, so
         * - This one *should* expand into two consecutive infix ::  :
         *
         *        [Pexp_apply]
         *          /      \
         *     first ::   [Pexp_apply]
         *                  /   \
         *              second :: third
         *
         *
         * - This one *shouldn't*:
         *
         *                [Pexp_apply]
         *                  /      \
         *       [  Pexp_apply  ] :: third
         *          /     \
         *       first ::  second
         *
         *
         * Sequential differing infix operators:
         * ------------------------------------
         *
         * Neither of the following require paren grouping because of rule 3.
         *
         *
         *        [Pexp_apply]
         *          /      \
         *     first  +  [Pexp_apply]
         *                  /   \
         *              second * third
         *
         *
         *                [Pexp_apply]
         *                  /      \
         *        [Pexp_apply  +  third
         *          /     \
         *       first *  second
         *
         *  The previous has nothing to do with the fact that + and * have the same
         *  associativity. Exception 3 applies to the following where :: is right assoc
         *  and + is left. + has higher precedence than ::
         *
         *  - so parens aren't required to group + when it is in a branch of a
         *    lower precedence ::
         *
         *        [Pexp_apply]
         *          /      \
         *     first ::   [Pexp_apply]
         *                  /   \
         *              second + third
         *
         *
         *  - Whereas there is no Exception that applies in this case (Exception 3
         *    doesn't apply) so parens are required around the :: in this case.
         *
         *                [Pexp_apply]
         *                  /      \
         *       [  Pexp_apply  ] + third
         *          /     \
         *       first ::  second
        *)

        method classExpressionToFormattedApplicationItems =
          function
          | { pcl_desc = Pcl_apply (ce, l); _ } ->
            [ label
                (self#simple_class_expr ce)
                (self#label_x_expression_params l)
            ]
          | x -> [ self#class_expr x ]

        method dotdotdotChild expr =
          let self = self#inline_braces in
          match expr with
          | { pexp_desc = Pexp_apply (funExpr, args); _ }
            when printedStringAndFixityExpr funExpr == Normal
                 && Reason_attributes.without_stylistic_attrs
                      expr.pexp_attributes
                    == [] ->
            (match
               self#formatFunAppl
                 ~prefix:(atom "...")
                 ~wrap:("{", "}")
                 ~jsxAttrs:[]
                 ~args
                 ~funExpr
                 ~applicationExpr:expr
                 ()
             with
            | [ x ] -> x
            | xs -> makeList xs)
          | { pexp_desc = Pexp_fun _; _ } ->
            self#formatPexpFun ~prefix:(atom "...") ~wrap:("{", "}") expr
          | _ ->
            (* Currently spreading a list must be wrapped in { }.
             * You can remove the entire even_wrap_simple arg when that is fixed. *)
            let even_wrap_simple =
              match expr with
              | { pexp_desc =
                    Pexp_construct
                      ( { txt = Lident "::"; _ }
                      , Some { pexp_desc = Pexp_tuple _; _ } )
                ; _
                } ->
                not (Reason_attributes.has_jsx_attributes expr.pexp_attributes)
              | _ -> false
            in
            let childLayout =
              self#dont_preserve_braces#simplifyUnparseExpr
                ~even_wrap_simple
                ~wrap:("{", "}")
                expr
            in
            makeList ~break:Never [ atom "..."; childLayout ]

        (*    How JSX is formatted/wrapped. We want the attributes to wrap independently
         *    of children.
         *
         *    <xxx
         *      attr1=blah
         *      attr2=foo>
         *      child
         *      child
         *      child
         *    </x>
         *
         *  +-------------------------------+
         *  |  left   right (list of attrs) |
         *  |   / \   /   \                 |
         *  |   <tag                        |
         *  |     attr1=blah                |
         *  |     attr2=foo                 |
         *  +-------------------------------+
         *   |
         *   |
         *   |
         *   |      left       right  list of children with
         *   |   /       \    /  \     open,close = > </tag>
         *   |  +---------+
         *   +--|         |    >
         *      +---------+
         *
         *      </tag>
        *)
        method formatJSXComponent componentName ?closeComponentName args =
          let self = self#inline_braces in
          let rec processArguments arguments processedAttrs children =
            match arguments with
            | (Labelled "children", { pexp_desc = Pexp_construct (_, None); _ })
              :: tail ->
              processArguments tail processedAttrs None
            | ( Labelled "children"
              , ({ pexp_desc =
                     Pexp_construct
                       ( { txt = Lident "::"; _ }
                       , Some { pexp_desc = Pexp_tuple _; _ } )
                 ; _
                 } as arg) )
              :: tail ->
              (match self#formatJsxChildrenNonSpread arg [] with
              (* Back out of the standard jsx child formatting *)
              | None ->
                processArguments
                  tail
                  processedAttrs
                  (Some [ self#dotdotdotChild arg ])
              | Some chldn -> processArguments tail processedAttrs (Some chldn))
            | (Labelled "children", expr) :: tail ->
              processArguments
                tail
                processedAttrs
                (Some [ self#dotdotdotChild expr ])
            | (Optional lbl, expression) :: tail ->
              let { Reason_attributes.jsxAttrs; _ } =
                Reason_attributes.partitionAttributes expression.pexp_attributes
              in
              let value_has_jsx = jsxAttrs != [] in
              let nextAttr =
                match expression.pexp_desc with
                | Pexp_ident ident when isPunnedJsxArg lbl ident ->
                  makeList ~break:Layout.Never [ atom "?"; atom lbl ]
                | Pexp_construct _ when value_has_jsx ->
                  label
                    (makeList ~break:Layout.Never [ atom lbl; atom "=?" ])
                    (self#simplifyUnparseExpr ~wrap:("{", "}") expression)
                | _ ->
                  label
                    (makeList ~break:Layout.Never [ atom lbl; atom "=?" ])
                    (self#dont_preserve_braces#simplifyUnparseExpr
                       ~wrap:("{", "}")
                       expression)
              in
              processArguments tail (nextAttr :: processedAttrs) children
            | (Labelled lbl, expression) :: tail ->
              let { Reason_attributes.jsxAttrs; _ } =
                Reason_attributes.partitionAttributes expression.pexp_attributes
              in
              let value_has_jsx = jsxAttrs != [] in
              let nextAttr =
                match expression.pexp_desc with
                | Pexp_ident ident when isPunnedJsxArg lbl ident -> atom lbl
                | _ when isJSXComponent expression ->
                  label
                    (atom (lbl ^ "="))
                    (makeList
                       ~break:IfNeed
                       ~wrap:("{", "}")
                       [ self#dont_preserve_braces#simplifyUnparseExpr
                           expression
                       ])
                | Pexp_open (me, e)
                  when self#isSeriesOfOpensFollowedByNonSequencyExpression
                         expression ->
                  label
                    (makeList
                       [ atom lbl
                       ; atom "="
                       ; label
                           (self#moduleExpressionToFormattedApplicationItems
                              me.popen_expr)
                           (atom ".")
                       ])
                    (self#formatNonSequencyExpression e)
                | Pexp_apply (({ pexp_desc = Pexp_ident _; _ } as funExpr), args)
                  when printedStringAndFixityExpr funExpr == Normal
                       && Reason_attributes.without_stylistic_attrs
                            expression.pexp_attributes
                          == [] ->
                  let lhs = makeList [ atom lbl; atom "=" ] in
                  (match
                     self#formatFunAppl
                       ~prefix:lhs
                       ~wrap:("{", "}")
                       ~jsxAttrs:[]
                       ~args
                       ~funExpr
                       ~applicationExpr:expression
                       ()
                   with
                  | [ x ] -> x
                  | xs -> makeList xs)
                | Pexp_apply (eFun, _) ->
                  let lhs = makeList [ atom lbl; atom "=" ] in
                  let rhs =
                    match printedStringAndFixityExpr eFun with
                    | Infix str when requireNoSpaceFor str ->
                      self#unparseExpr expression
                    | _ ->
                      self#dont_preserve_braces#simplifyUnparseExpr
                        ~wrap:("{", "}")
                        expression
                  in
                  label lhs rhs
                | Pexp_construct _ when value_has_jsx ->
                  label
                    (makeList [ atom lbl; atom "=" ])
                    (self#simplifyUnparseExpr ~wrap:("{", "}") expression)
                | Pexp_record _ | Pexp_construct _ | Pexp_array _ | Pexp_tuple _
                | Pexp_match _ | Pexp_extension _ | Pexp_function _ ->
                  label
                    (makeList [ atom lbl; atom "=" ])
                    (self#dont_preserve_braces#simplifyUnparseExpr
                       ~wrap:("{", "}")
                       expression)
                | Pexp_fun _ ->
                  let propName = makeList [ atom lbl; atom "=" ] in
                  self#formatPexpFun
                    ~wrap:("{", "}")
                    ~prefix:propName
                    expression
                | _ ->
                  makeList
                    [ atom lbl
                    ; atom "="
                    ; self#dont_preserve_braces#simplifyUnparseExpr
                        ~wrap:("{", "}")
                        expression
                    ]
              in
              processArguments tail (nextAttr :: processedAttrs) children
            | [] -> processedAttrs, children
            | _ :: tail -> processArguments tail processedAttrs children
          in
          let reversedAttributes, children = processArguments args [] None in
          match children with
          | None ->
            makeList
              ~break:IfNeed
              ~wrap:("<" ^ componentName, "/>")
              ~pad:(true, true)
              ~inline:(false, false)
              ~postSpace:true
              (List.rev reversedAttributes)
          | Some renderedChildren ->
            let openTagAndAttrs =
              match reversedAttributes with
              | [] -> atom ("<" ^ componentName ^ ">")
              | revAttrHd :: revAttrTl ->
                let finalAttrList =
                  List.rev
                    (makeList ~break:Layout.Never [ revAttrHd; atom ">" ]
                    :: revAttrTl)
                in
                let renderedAttrList =
                  makeList
                    ~inline:(true, true)
                    ~break:IfNeed
                    ~pad:(false, false)
                    ~preSpace:true
                    finalAttrList
                in
                label ~space:true (atom ("<" ^ componentName)) renderedAttrList
            in
            label
              openTagAndAttrs
              (makeList
                 ~wrap:
                   ( ""
                   , "</"
                     ^ (match closeComponentName with
                       | None -> componentName
                       | Some close -> close)
                     ^ ">" )
                 ~inline:(true, false)
                 ~break:IfNeed
                 ~pad:(true, true)
                 ~postSpace:true
                 renderedChildren)

        (* Format Pexp_fun expression: (a, b) => a + b;
         * Example: the `onClick` prop with Pexp_fun in
         *  <div
         *    onClick={(event) => {
         *      Js.log(event);
         *      handleChange(event);
         *    }}
         *  />;
         *
         *  The arguments of the callback (Pexp_fun) should be inlined as much as
         *  possible on the same line as `onClick={`.
         *  Also notice the brace-hugging `}}` at the end.
         *
         *  ~prefix -> prefixes the Pexp_fun layout, example `onClick=`
         *  ~wrap -> wraps the `Pexp_fun` in the tuple passed to wrap, e.g. `{` and
         *  `}` for jsx
        *)
        method formatPexpFun ?(prefix = atom "") ?(wrap = "", "") expression =
          let lwrap, rwrap = wrap in
          let { Reason_attributes.stdAttrs; uncurried; _ } =
            Reason_attributes.partitionAttributes expression.pexp_attributes
          in
          if uncurried then Hashtbl.add uncurriedTable expression.pexp_loc true;

          let args, ret =
            (* omit attributes here, we're formatting them manually *)
            self#curriedPatternsAndReturnVal
              { expression with pexp_attributes = [] }
          in
          (* Format `onClick={` *)
          let propName = makeList ~wrap:("", lwrap) [ prefix ] in
          let argsList =
            let args =
              match args with [ argsList ] -> argsList | args -> makeList args
            in
            match stdAttrs with
            | [] -> args
            | attrs ->
              (* attach attributes to the args of the Pexp_fun: `[@attr]
                 (event)` *)
              let attrList =
                makeList
                  ~inline:(true, true)
                  ~break:IfNeed
                  ~postSpace:true
                  (List.map self#attribute attrs)
              in
              let all = [ attrList; args ] in
              makeList ~break:IfNeed ~inline:(true, true) ~postSpace:true all
          in
          (* Format `onClick={(event)` *)
          let propNameWithArgs = label propName argsList in
          (* Pick constraints: (a, b) :string => ...
           * :string is the constraint here *)
          let return, optConstr =
            match ret.pexp_desc with
            | Pexp_constraint (e, ct) -> e, Some (self#non_arrowed_core_type ct)
            | _ -> ret, None
          in
          let returnExpr, leftWrap =
            match self#letList return with
            | [ x ] ->
              (* Format `handleChange(event)}` or
               *  handleChange(event)
               * }
               *
               * If the closing rwrap is empty, we need it to be inline, otherwise
               * we get a empty newline when the layout breaks:
               * ```
               *  handleChange(event)
               *
               * ```
               * (Notice to nonsense newline)
              *)
              let shouldPreserveBraces =
                self#should_preserve_requested_braces return
              in
              let rwrap = if shouldPreserveBraces then "}" ^ rwrap else rwrap in
              let inlineClosing = rwrap = "" in
              let layout =
                makeList
                  ~break:IfNeed
                  ~inline:(true, inlineClosing)
                  ~wrap:("", rwrap)
                  [ x ]
              in
              layout, if shouldPreserveBraces then "{" else ""
            | xs ->
              (* Format `Js.log(event)` and `handleChange(event)` as
               * {
               *   Js.log(event);
               *   handleChange(event);
               * }}
              *)
              let layout =
                makeList
                  ~break:Always_rec
                  ~sep:(SepFinal (";", ";"))
                  ~wrap:("{", "}" ^ rwrap)
                  xs
              in
              layout, ""
          in
          match optConstr with
          | Some typeConstraint ->
            let upToConstraint =
              label
                ~space:true
                (makeList ~wrap:("", ":") [ propNameWithArgs ])
                typeConstraint
            in
            label
              (makeList ~wrap:("", " => " ^ leftWrap) [ upToConstraint ])
              returnExpr
          | None ->
            label
              (makeList ~wrap:("", " => " ^ leftWrap) [ propNameWithArgs ])
              returnExpr

        (* Creates a list of simple module expressions corresponding to module
           expression or functor application. *)
        method moduleExpressionToFormattedApplicationItems ?(prefix = "") x =
          match x with
          (* are we formatting a functor application with a module structure as arg?
           * YourLib.Make({
           *   type t = int;
           *   type s = string;
           * });
           *
           * We should "hug" the parens here: ({ & }) should stick together.
          *)
          | { pmod_desc =
                Pmod_apply
                  ( ({ pmod_desc = Pmod_ident _; _ } as m1)
                  , ({ pmod_desc = Pmod_structure _; _ } as m2) )
            ; _
            } ->
            let modIdent =
              source_map ~loc:m1.pmod_loc (self#simple_module_expr m1)
            in
            let name =
              if prefix <> ""
              then makeList ~postSpace:true [ atom prefix; modIdent ]
              else modIdent
            in
            let arg =
              source_map ~loc:m2.pmod_loc (self#simple_module_expr ~hug:true m2)
            in
            label name arg
          | _ ->
            let rec extract_apps args = function
              | { pmod_desc = Pmod_apply (me1, me2); _ } ->
                let arg =
                  source_map ~loc:me2.pmod_loc (self#simple_module_expr me2)
                in
                extract_apps (arg :: args) me1
              | me ->
                let head = source_map ~loc:me.pmod_loc (self#module_expr me) in
                if args == [] then head else label head (makeTup args)
            in
            let functor_application = extract_apps [] x in
            if prefix <> ""
            then makeList ~postSpace:true [ atom prefix; functor_application ]
            else functor_application

        (* Watch out, if you see something like below (sixteenTuple getting put on a
         * newline), yet a paren-wrapped list wouldn't have had an extra newlin, you
         * might need to wrap the single token (sixteenTuple) in [ensureSingleTokenSticksToLabel].
         * let (
         *    axx,
         *    oxx,
         *    pxx
         *  ):
         *    sixteenTuple = echoTuple (
         *    0,
         *    0,
         *    0
         *  );
        *)

        method formatSimplePatternBinding
          labelOpener
          layoutPattern
          typeConstraint
          appTerms =
          let letPattern =
            label ~break:`Never ~space:true (atom labelOpener) layoutPattern
          in
          let upUntilEqual =
            match typeConstraint with
            | None -> letPattern
            | Some tc -> formatTypeConstraint letPattern tc
          in
          let includingEqual =
            makeList ~postSpace:true [ upUntilEqual; atom "=" ]
          in
          formatAttachmentApplication
            applicationFinalWrapping
            (Some (true, includingEqual))
            appTerms

        (* The [bindingLabel] is either the function name (if let binding) or first
         * arg (if lambda).
         *
         * For defining layout of the following form:
         *
         *     lbl one
         *         two
         *         constraint => {
         *       ...
         *     }
         *
         * If using "=" as the arrow, can also be used for:
         *
         *     met private
         *         myMethod
         *         constraint = fun ...
         *
        *)
        method wrapCurriedFunctionBinding
          ?attachTo
          ~arrow
          ?(sweet = false)
          ?(spaceBeforeArrow = true)
          prefixText
          bindingLabel
          patternList
          returnedAppTerms =
          let allPatterns = bindingLabel :: patternList in
          let partitioning = curriedFunctionFinalWrapping allPatterns in
          let everythingButReturnVal =
            (* Because align_closing is set to false, you get:
             *
             * (Brackets[] inserted to show boundaries between open/close of pattern list)
             * let[firstThing
             *     secondThing
             *     thirdThing]
             *
             * It only wraps to indent four by coincidence: If the "opening" token was
             * longer, you'd get:
             *
             * letReallyLong[firstThing
             *               secondThing
             *               thirdThing]
             *
             * For curried let bindings, we stick the arrow in the *last* pattern:
             * let[firstThing
             *     secondThing
             *     thirdThing =>]
             *
             * But it could have just as easily been the "closing" token corresponding to
             * "let". This works because we have [align_closing = false]. The benefit of
             * shoving it in the last pattern, is that we can turn [align_closing = true]
             * and still have the arrow stuck to the last pattern (which is usually what we
             * want) (See modeTwo below).
            *)
            match partitioning with
            | None when sweet ->
              makeList
                ~pad:(false, spaceBeforeArrow)
                ~wrap:("", arrow)
                ~indent:(settings.space * settings.indentWrappedPatternArgs)
                ~postSpace:true
                ~inline:(true, true)
                ~break:IfNeed
                allPatterns
            | None ->
              (* We want the binding label to break *with* the arguments. Again,
                 there's no apparent way to add additional indenting for the
                 args with this setting. *)

              (* Formats lambdas by treating the first pattern as the
               * "bindingLabel" which is kind of strange in some cases (when
               * you only have one arg that wraps)...
               *
               *    echoTheEchoer (
               *      fun (
               *            a,
               *            p
               *          ) => (
               *        a,
               *        b
               *      )
               *
               * But it makes sense in others (where you have multiple args):
               *
               *    echoTheEchoer (
               *      fun (
               *            a,
               *            p
               *          )
               *          mySecondArg
               *          myThirdArg => (
               *        a,
               *        b
               *      )
               *
               * Try any other convention for wrapping that first arg and it
               * won't look as balanced when adding multiple args.
              *)
              makeList
                ~pad:(true, spaceBeforeArrow)
                ~wrap:(prefixText, arrow)
                ~indent:(settings.space * settings.indentWrappedPatternArgs)
                ~postSpace:true
                ~inline:(true, true)
                ~break:IfNeed
                allPatterns
            | Some (attachedList, wrappedListy) ->
              (* To get *only* the final argument to "break", while not
                 necessarily breaking the prior arguments, we dock everything
                 but the last item to a created label *)
              label
                ~space:true
                (makeList
                   ~pad:(true, spaceBeforeArrow)
                   ~wrap:(prefixText, arrow)
                   ~indent:(settings.space * settings.indentWrappedPatternArgs)
                   ~postSpace:true
                   ~inline:(true, true)
                   ~break:IfNeed
                   attachedList)
                wrappedListy
          in

          let everythingButAppTerms =
            match attachTo with
            | None -> everythingButReturnVal
            | Some toThis -> label ~space:true toThis everythingButReturnVal
          in
          formatAttachmentApplication
            applicationFinalWrapping
            (Some (true, everythingButAppTerms))
            returnedAppTerms

        method leadingCurriedAbstractTypes x =
          let rec argsAndReturn xx =
            match xx.pexp_desc with
            | Pexp_newtype (str, e) ->
              let nextArgs, return = argsAndReturn e in
              str :: nextArgs, return
            | _ -> [], xx.pexp_desc
          in
          argsAndReturn x

        method curriedConstructorPatternsAndReturnVal cl =
          let rec argsAndReturn args = function
            | { pcl_desc = Pcl_fun (label, eo, p, e); pcl_attributes = []; _ }
              ->
              let arg =
                source_map ~loc:p.ppat_loc (self#label_exp label eo p)
              in
              argsAndReturn (arg :: args) e
            | xx ->
              if args == []
              then None, xx
              else Some (makeTup (List.rev args)), xx
          in
          argsAndReturn [] cl

        (* Returns the arguments list (if any, that occur before the =>), and
           the final expression (that is either returned from the function
           (after =>) or that is bound to the value (if there are no arguments,
           and this is just a let pattern binding)). *)
        method curriedPatternsAndReturnVal x =
          let uncurried =
            try Hashtbl.find uncurriedTable x.pexp_loc with Not_found -> false
          in
          let rec extract_args xx =
            let { Reason_attributes.stdAttrs; _ } =
              Reason_attributes.partitionAttributes
                ~allowUncurry:false
                xx.pexp_attributes
            in
            if stdAttrs != []
            then [], xx
            else
              match xx.pexp_desc with
              (* label * expression option * pattern * expression *)
              | Pexp_fun (l, eo, p, e) ->
                let args, ret = extract_args e in
                `Value (l, eo, p) :: args, ret
              | Pexp_newtype (newtype, e) ->
                let args, ret = extract_args e in
                `Type newtype :: args, ret
              | Pexp_constraint _ -> [], xx
              | _ -> [], xx
          in
          let prepare_arg = function
            | `Value (l, eo, p) ->
              source_map ~loc:p.ppat_loc (self#label_exp l eo p)
            | `Type nt -> atom ("type " ^ nt.txt)
          in
          let single_argument_no_parens p ret =
            if uncurried
            then false
            else
              let isUnitPat = is_unit_pattern p in
              let isAnyPat = is_any_pattern p in
              match ret.pexp_desc with
              (* (event) :ReasonReact.event => {...}
               * The above Pexp_fun with constraint ReasonReact.event requires parens
               * surrounding the single argument `event`.*)
              | Pexp_constraint _ when (not isUnitPat) && not isAnyPat -> false
              | _ -> isUnitPat || isAnyPat || is_ident_pattern p
          in
          match extract_args x with
          | [], ret -> [], ret
          | [ `Value (Nolabel, None, p) ], ret
            when is_unit_pattern p && uncurried ->
            [ atom "(.)" ], ret
          | [ (`Value (Nolabel, None, p) as arg) ], ret
            when single_argument_no_parens p ret ->
            [ prepare_arg arg ], ret
          | args, ret -> [ makeTup ~uncurried (List.map prepare_arg args) ], ret

        (* Returns the (curriedModule, returnStructure) for a functor *)
        method curriedFunctorPatternsAndReturnStruct =
          function
          (* string loc * module_type option * module_expr *)
          | { pmod_desc = Pmod_functor (fp, me2); _ } ->
            let firstOne =
              match fp with
              | Unit -> atom ""
              | Named (s, mt') ->
                let s = moduleIdent s in
                self#module_type (makeList [ atom s; atom ":" ]) mt'
            in
            let functorArgsRecurse, returnStructure =
              self#curriedFunctorPatternsAndReturnStruct me2
            in
            firstOne :: functorArgsRecurse, returnStructure
          | me -> [], me

        method isRenderableAsPolymorphicAbstractTypes
          typeVars
          polyType
          leadingAbstractVars
          nonVarifiedType =
          same_ast_modulo_varification_and_extensions polyType nonVarifiedType
          && for_all2' string_loc_equal typeVars leadingAbstractVars

        (* Reinterpret this as a pattern constraint since we don't currently have a
         * way to disambiguate. There is currently a way to disambiguate a parsing
         * from Ppat_constraint vs.  Pexp_constraint. Currently (and consistent with
         * OCaml standard parser):

         *   let (x: typ) = blah;
         *     Becomes Ppat_constraint
         *   let x:poly . type = blah;
         *     Becomes Ppat_constraint
         *   let x:typ = blah;
         *     Becomes Pexp_constraint(ghost)
         *   let x = (blah:typ);
         *     Becomes Pexp_constraint(ghost)
         *
         * How are double constraints represented?
         * let (x:typ) = (blah:typ);
         * If currently both constraints are parsed into a single Pexp_constraint,
         * then something must be lost, and how could you fail type checking on:
         * let x:int = (10:string) ?? Answer: It probably parses into a nested
         * Pexp_constraint.
         *
         * Proposal:
         *
         *   let (x: typ) = blah;
         *     Becomes Ppat_constraint   (still)
         *   let x:poly . type = blah;
         *     Becomes Ppat_constraint   (still)
         *   let x:typ = blah;
         *     Becomes Ppat_constraint
         *   let x = blah:typ;
         *     Becomes Pexp_constraint
         *
         *
         * Reasoning: Allows parsing of any of the currently valid ML forms, but
         * combines the two most similar into one form. The only lossyness is the
         * unnecessary parens, which there is already precedence for dropping in
         * expressions. In the existing approach, preserving a paren-constrained
         * expression is *impossible* because it becomes pretty printed as
         * let x:t =.... In the proposal, it is not impossible - it is only
         * impossible to preserve unnecessary parenthesis around the let binding.
         *
         * The one downside is that integrating with existing code that uses [let x =
         * (blah:typ)] in standard OCaml will be parsed as a Pexp_constraint. There
         * might be some lossiness (beyond parens) that occurs in the original OCaml
         * parser.
        *)

        method locallyAbstractPolymorphicFunctionBinding
          prefixText
          layoutPattern
          funWithNewTypes
          absVars
          bodyType =
          let appTerms = self#unparseExprApplicationItems funWithNewTypes in
          let locallyAbstractTypes = List.map (fun x -> atom x.txt) absVars in
          let typeLayout =
            source_map ~loc:bodyType.ptyp_loc (self#core_type bodyType)
          in
          let polyType =
            label
              ~space:true
              (* TODO: This isn't a correct use of sep! It ruins how
               * comments are interleaved. *)
              (makeList
                 [ makeList ~sep:(Sep " ") (atom "type" :: locallyAbstractTypes)
                 ; atom "."
                 ])
              typeLayout
          in
          self#formatSimplePatternBinding
            prefixText
            layoutPattern
            (Some polyType)
            appTerms

        (*  Intelligently switches between:
         *  Curried function binding w/ constraint on return expr:
         *     lbl patt
         *         pattAux
         *         arg
         *         :constraint => {
         *       ...
         *     }
         *
         *  Constrained:
         *     lbl patt
         *         pattAux...
         *         :constraint = {
         *       ...
         *     }
        *)
        method wrappedBinding prefixText ~arrow pattern patternAux expr =
          let expr = self#process_underscore_application expr in
          let argsList, return = self#curriedPatternsAndReturnVal expr in
          let patternList =
            match patternAux with
            | [] -> pattern
            | _ :: _ ->
              makeList
                ~postSpace:true
                ~inline:(true, true)
                ~break:IfNeed
                (pattern :: patternAux)
          in
          match argsList, return.pexp_desc with
          | [], Pexp_constraint (e, ct) ->
            let typeLayout =
              source_map
                ~loc:ct.ptyp_loc
                (match ct.ptyp_desc with
                | Ptyp_package (li, cstrs) -> self#typ_package li cstrs
                | _ -> self#core_type ct)
            in
            let appTerms = self#unparseExprApplicationItems e in
            self#formatSimplePatternBinding
              prefixText
              patternList
              (Some typeLayout)
              appTerms
          | [], _ ->
            (* simple let binding, e.g. `let number = 5` *)
            (* let f = (. a, b) => a + b; *)
            let appTerms = self#unparseExprApplicationItems expr in
            self#formatSimplePatternBinding prefixText patternList None appTerms
          | _ :: _, _ ->
            let argsWithConstraint, actualReturn =
              self#normalizeFunctionArgsConstraint argsList return
            in
            let fauxArgs = List.concat [ patternAux; argsWithConstraint ] in
            let returnedAppTerms =
              self#unparseExprApplicationItems actualReturn
            in
            (* Attaches the `=` to `f` to recreate javascript function syntax in
             * let f = (a, b) => a + b; *)
            let lbl =
              makeList ~sep:(Sep " ") ~break:Layout.Never [ pattern; atom "=" ]
            in
            self#wrapCurriedFunctionBinding
              prefixText
              ~arrow
              lbl
              fauxArgs
              returnedAppTerms

        (* Similar to the above method. *)
        method wrappedClassBinding prefixText pattern patternAux expr =
          let args, return = self#curriedConstructorPatternsAndReturnVal expr in
          let patternList =
            match patternAux with
            | [] -> pattern
            | _ :: _ ->
              makeList
                ~postSpace:true
                ~inline:(true, true)
                ~break:IfNeed
                (pattern :: patternAux)
          in
          match args, return.pcl_desc with
          | None, Pcl_constraint (e, ct) ->
            let typeLayout =
              source_map ~loc:ct.pcty_loc (self#class_constructor_type ct)
            in
            self#formatSimplePatternBinding
              prefixText
              patternList
              (Some typeLayout)
              (self#classExpressionToFormattedApplicationItems e, None)
          | None, _ ->
            self#formatSimplePatternBinding
              prefixText
              patternList
              None
              (self#classExpressionToFormattedApplicationItems expr, None)
          | Some args, _ ->
            let argsWithConstraint, actualReturn =
              self#normalizeConstructorArgsConstraint [ args ] return
            in
            let fauxArgs = List.concat [ patternAux; argsWithConstraint ] in
            self#wrapCurriedFunctionBinding
              prefixText
              ~arrow:"="
              pattern
              fauxArgs
              ( self#classExpressionToFormattedApplicationItems actualReturn
              , None )

        (* Attaches doc comments to a layout, with whitespace preserved
         * Example:
         * /** Doc comment */
         *
         * /* another random comment */
         * let a = 1;
        *)
        method attachDocAttrsToLayout
          ~(* all std attributes attached on the ast node backing the
                layout *)
          (stdAttrs : Parsetree.attributes)
          ~(* all doc comments attached on the ast node backing the layout *)
          (docAttrs : Parsetree.attributes)
          ~(* location of the layout *)
           loc
          ~(* layout to attach the doc comments to *)
           layout
          () =
          (* compute the correct location of layout
           * Example:
           * 1| /** doc-comment */
           * 2|
           * 3| [@attribute]
           * 4| let a = 1;
           *
           * The location might indicate a start of line 4 for the ast-node
           * representing `let a = 1`. The reality is that `[@attribute]` should be
           * included (start of line 3), to represent the correct start location
           * of the whole layout.
          *)
          let loc =
            match stdAttrs with
            | { attr_name = astLoc; _ } :: _ -> astLoc.loc
            | [] -> loc
          in
          let rec aux prevLoc layout = function
            | ({ attr_name = x; _ } as attr : Parsetree.attribute) :: xs ->
              let newLayout =
                let range = Range.makeRangeBetween x.loc prevLoc in
                let layout =
                  if Range.containsWhitespace ~range ~comments:self#comments ()
                  then
                    let region = WhitespaceRegion.make ~range ~newlines:1 () in
                    Layout.Whitespace (region, layout)
                  else layout
                in
                makeList
                  ~inline:(true, true)
                  ~break:Always
                  [ self#attribute attr; layout ]
              in
              aux x.loc newLayout xs
            | [] -> layout
          in
          aux loc layout (List.rev docAttrs)

        method value_binding
          prefixText
          { pvb_pat; pvb_attributes; pvb_loc; pvb_expr } =
          self#binding
            prefixText
            ~attrs:pvb_attributes
            ~loc:pvb_loc
            ~pat:pvb_pat
            pvb_expr

        method binding_op prefixText { pbop_pat; pbop_loc; pbop_exp; _ } =
          self#binding
            (Reason_syntax_util.escape_stars_slashes prefixText)
            ~loc:pbop_loc
            ~pat:pbop_pat
            pbop_exp

        method binding prefixText ?(attrs = []) ~loc ~pat expr =
          (* TODO: print attributes *)
          let body =
            match pat.ppat_attributes, pat.ppat_desc with
            | [], Ppat_var _ ->
              self#wrappedBinding
                prefixText
                ~arrow:"=>"
                (source_map ~loc:pat.ppat_loc (self#simple_pattern pat))
                []
                expr
            (* Ppat_constraint is used in bindings of the form
             *
             *    let (inParenVar:typ) = ...
             *
             * And in the case of let bindings for explicitly polymorphic type
             * annotations (see parser for more details).
             *
             * See reason_parser.mly for explanation of how we encode the two primary
             * forms of explicit polymorphic annotations in the parse tree, and how
             * we must recover them here.
            *)
            | [], Ppat_open (lid, { ppat_desc = Ppat_record (l, closed); _ }) ->
              (* Special case handling for:
               *
               * let Foo.{
               *   destruct1,
               *   destruct2,
               *   destruct3,
               *   destruct4,
               *   destruct5,
               * } = bar;
              *)
              let upUntilEqual =
                let pat = self#patternRecord l closed in
                label
                  (label
                     ~space:true
                     (atom prefixText)
                     (label (self#longident_loc lid) (atom ".")))
                  pat
              in
              let appTerms = self#unparseExprApplicationItems expr in
              let includingEqual =
                makeList ~postSpace:true [ upUntilEqual; atom "=" ]
              in
              formatAttachmentApplication
                applicationFinalWrapping
                (Some (true, includingEqual))
                appTerms
            | [], Ppat_constraint (p, ty) ->
              (* Locally abstract forall types are *seriously* mangled by the parsing
               * stage, and we have to be very smart about how to recover it.
               *
               *  let df_locallyAbstractFuncAnnotated:
               *    type a b.
               *      a =>
               *      b =>
               *      (inputEchoRecord a, inputEchoRecord b) =
               *    fun (input: a) (input2: b) => (
               *      {inputIs: input},
               *      {inputIs: input2}
               *    );
               *
               * becomes:
               *
               *   let df_locallyAbstractFuncAnnotatedTwo:
               *     'a 'b .
               *     'a => 'b => (inputEchoRecord 'a, inputEchoRecord 'b)
               *    =
               *     fun (type a) (type b) => (
               *       fun (input: a) (input2: b) => ({inputIs: input}, {inputIs:input2}):
               *         a => b => (inputEchoRecord a, inputEchoRecord b)
               *     );
              *)
              let layoutPattern =
                source_map ~loc:pat.ppat_loc (self#simple_pattern p)
              in
              let leadingAbsTypesAndExpr =
                self#leadingCurriedAbstractTypes expr
              in
              (match p.ppat_desc, ty.ptyp_desc, leadingAbsTypesAndExpr with
              | ( Ppat_var _
                , Ptyp_poly (typeVars, varifiedPolyType)
                , ( (_ :: _ as absVars)
                  , Pexp_constraint (funWithNewTypes, nonVarifiedExprType) ) )
                when self#isRenderableAsPolymorphicAbstractTypes
                       typeVars
                       (* If even artificially varified - don't know until
                          returns*)
                       varifiedPolyType
                       absVars
                       nonVarifiedExprType ->
                (* We assume was the case whenever we see this pattern in the
                 * AST, it was because the parser parsed the polymorphic locally
                 * abstract type sugar.
                 *
                 * Ppat_var..Ptyp_poly...Pexp_constraint:
                 *
                 *    let x: 'a 'b . 'a => 'b => 'b =
                 *      fun (type a) (type b) =>
                 *         (fun aVal bVal => bVal : a => b => b);
                 *
                 * We need to be careful not to accidentally detect similar
                 * forms, that cannot be printed as sugar.
                 *
                 *    let x: 'a 'b . 'a => 'b => 'b =
                 *      fun (type a) (type b) =>
                 *         (fun aVal bVal => bVal : int => int => int);
                 *
                 * Should *NOT* be formatted as:
                 *
                 *    let x: type a b. int => int => int = fun aVal bVal => bVal;
                 *
                 * The helper function
                 * [same_ast_modulo_varification_and_extensions] was created to
                 * help compare the varified constraint pattern body, and the
                 * non-varified expression constraint type.
                 *
                 * The second requirement that we check before assuming that the
                 * sugar form is correct, is to make sure the list of type vars
                 * corresponds to a leading prefix of the Pexp_newtype variables.
                *)
                self#locallyAbstractPolymorphicFunctionBinding
                  prefixText
                  layoutPattern
                  funWithNewTypes
                  absVars
                  nonVarifiedExprType
              | _ ->
                let typeLayout =
                  source_map ~loc:ty.ptyp_loc (self#core_type ty)
                in
                let appTerms = self#unparseExprApplicationItems expr in
                self#formatSimplePatternBinding
                  prefixText
                  layoutPattern
                  (Some typeLayout)
                  appTerms)
            | _ ->
              let layoutPattern =
                source_map ~loc:pat.ppat_loc (self#pattern pat)
              in
              let appTerms = self#unparseExprApplicationItems expr in
              self#formatSimplePatternBinding
                prefixText
                layoutPattern
                None
                appTerms
          in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes ~partDoc:true attrs
          in
          let body = makeList ~inline:(true, true) [ body ] in
          let layout =
            self#attach_std_item_attrs stdAttrs (source_map ~loc body)
          in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:pat.ppat_loc
            ~layout
            ()

        (* Ensures that the constraint is formatted properly for sake of
           function binding (formatted without arrows) let x y z :
           no_unguarded_arrows_allowed_here => ret; *)
        method normalizeFunctionArgsConstraint argsList return =
          match return.pexp_desc with
          | Pexp_constraint (e, ct) ->
            let typeLayout =
              source_map
                ~loc:ct.ptyp_loc
                (self#non_arrowed_non_simple_core_type ct)
            in
            ( [ makeList
                  ~break:IfNeed
                  ~inline:(true, true)
                  (argsList @ [ formatJustTheTypeConstraint typeLayout ])
              ]
            , e )
          | _ -> argsList, return

        method normalizeConstructorArgsConstraint argsList return =
          match return.pcl_desc with
          | Pcl_constraint (e, ct) when return.pcl_attributes == [] ->
            let typeLayout =
              source_map
                ~loc:ct.pcty_loc
                (self#non_arrowed_class_constructor_type ct)
            in
            argsList @ [ formatJustTheTypeConstraint typeLayout ], e
          | _ -> argsList, return

        method bindingsLocationRange ?extension l =
          let len = List.length l in
          let fstLoc =
            match extension with
            | Some ({ pexp_loc = { loc_ghost = false; _ }; _ } as ext) ->
              ext.pexp_loc
            | _ -> (List.nth l 0).pvb_loc
          in
          let lstLoc = (List.nth l (len - 1)).pvb_loc in
          { loc_start = fstLoc.loc_start
          ; loc_end = lstLoc.loc_end
          ; loc_ghost = false
          }

        method bindingOpsLocationRange { let_; ands; _ } =
          let fstLoc = let_.pbop_loc in
          let lstLoc =
            match ands with
            | [] -> fstLoc
            | xs ->
              let len = List.length xs in
              (List.nth xs (len - 1)).pbop_loc
          in
          { loc_start = fstLoc.loc_start
          ; loc_end = lstLoc.loc_end
          ; loc_ghost = false
          }

        method bindings ?extension (rf, l) =
          let label = add_extension_sugar "let" extension in
          let label =
            match rf with Nonrecursive -> label | Recursive -> label ^ " rec"
          in
          match l with
          | [ x ] -> self#value_binding label x
          | l ->
            let items =
              List.mapi
                (fun i x ->
                   let loc = extractLocValBinding x in
                   let layout =
                     self#value_binding (if i == 0 then label else "and") x
                   in
                   loc, layout)
                l
            in
            let itemsLayout =
              groupAndPrint
                ~xf:(fun (_, layout) -> layout)
                ~getLoc:(fun (loc, _) -> loc)
                ~comments:self#comments
                items
            in
            makeList
              ~postSpace:true
              ~break:Always
              ~indent:0
              ~inline:(true, true)
              itemsLayout

        method letop_bindings { let_; ands; _ } =
          let label =
            Reason_syntax_util.compress_letop_identifier let_.pbop_op.txt
          in
          let let_item = self#binding_op label let_ in
          match ands with
          | [] -> let_item
          | l ->
            let and_items =
              List.map
                (fun x ->
                   let loc = extractLocBindingOp x in
                   let layout =
                     self#binding_op
                       (Reason_syntax_util.compress_letop_identifier
                          x.pbop_op.txt)
                       x
                   in
                   loc, layout)
                l
            in
            let itemsLayout =
              groupAndPrint
                ~xf:(fun (_, layout) -> layout)
                ~getLoc:(fun (loc, _) -> loc)
                ~comments:self#comments
                ((extractLocBindingOp let_, let_item) :: and_items)
            in
            makeList
              ~postSpace:true
              ~break:Always
              ~indent:0
              ~inline:(true, true)
              itemsLayout

        method pexp_open ~attrs ?extension expr me =
          let openLayout =
            label
              ~space:true
              (atom
                 (add_open_extension_sugar
                    ~override:me.popen_override
                    extension))
              (self#moduleExpressionToFormattedApplicationItems me.popen_expr)
          in
          let attrsOnOpen =
            makeList
              ~inline:(true, true)
              ~postSpace:true
              ~break:Always
              (self#attributes attrs @ [ openLayout ])
          in
          (* Just like the bindings, have to synthesize a location since the *
             Pexp location is parsed (potentially) beginning with the open *
             brace {} in the let sequence. *)
          let layout = source_map ~loc:me.popen_loc attrsOnOpen in
          let loc =
            { me.popen_loc with
              loc_start =
                { me.popen_loc.loc_start with
                  pos_lnum = expr.pexp_loc.loc_start.pos_lnum
                }
            }
          in
          loc, layout

        method letList expr =
          let letModuleBinding ?extension s me =
            let prefixText = add_extension_sugar "module" extension in
            let bindingName = atom ~loc:s.loc (moduleIdent s) in
            let moduleExpr = me in
            let letModuleLayout =
              self#let_module_binding prefixText bindingName moduleExpr
            in
            let letModuleLoc =
              { loc_start = s.loc.loc_start
              ; loc_end = me.pmod_loc.loc_end
              ; loc_ghost = false
              }
            in
            (* Just like the bindings, have to synthesize a location since the
             * Pexp location is parsed (potentially) beginning with the open
             * brace {} in the let sequence. *)
            let layout = source_map ~loc:letModuleLoc letModuleLayout in
            let _, return =
              self#curriedFunctorPatternsAndReturnStruct moduleExpr
            in
            let loc = { letModuleLoc with loc_end = return.pmod_loc.loc_end } in
            loc, layout
          in
          (* Recursively transform a nested ast of "let-items", into a flat
           * list containing the location indicating start/end of the "let-item" and
           * its layout. *)
          let rec processLetList acc expr =
            let { Reason_attributes.stdAttrs
                ; arityAttrs
                ; jsxAttrs
                ; stylisticAttrs
                ; _
                }
              =
              Reason_attributes.partitionAttributes
                ~allowUncurry:false
                expr.pexp_attributes
            in
            match stdAttrs, expr.pexp_desc with
            | [], Pexp_let (rf, l, e) ->
              (* For "letList" bindings, the start/end isn't as simple as with
               * module value bindings. For "let lists", the sequences were formed
               * within braces {}. The parser relocates the first let binding to the
               * first brace. *)
              let bindingsLayout = self#bindings (rf, l) in
              let bindingsLoc = self#bindingsLocationRange l in
              let layout = source_map ~loc:bindingsLoc bindingsLayout in
              processLetList ((bindingsLoc, layout) :: acc) e
            | attrs, Pexp_letop ({ body; _ } as op) ->
              (* For "letList" bindings, the start/end isn't as simple as with
               * module value bindings. For "let lists", the sequences were formed
               * within braces {}. The parser relocates the first let binding to the
               * first brace. *)
              let bindingsLayout = self#letop_bindings op in
              let bindingsLoc = self#bindingOpsLocationRange op in
              let bindingsLayout =
                makeList
                  ~break:IfNeed
                  ~inline:(true, true)
                  ~postSpace:true
                  (self#attributes attrs @ [ bindingsLayout ])
              in
              let layout = source_map ~loc:bindingsLoc bindingsLayout in
              processLetList ((bindingsLoc, layout) :: acc) body
            | attrs, Pexp_open (me, e)
            (* Add this when check to make sure these are handled as regular
               "simple expressions" *)
              when not
                     (self#isSeriesOfOpensFollowedByNonSequencyExpression
                        { expr with pexp_attributes = [] }) ->
              if Reason_attributes.has_open_notation_attr stylisticAttrs
              then
                ( Location.none
                , label
                    (label
                       (self#moduleExpressionToFormattedApplicationItems
                          me.popen_expr)
                       (atom "."))
                    (makeLetSequence ~wrap:("(", ")") (self#letList e)) )
                :: acc
              else
                let loc, layout = self#pexp_open ~attrs expr me in
                processLetList ((loc, layout) :: acc) e
            | [], Pexp_letmodule (s, me, e) ->
              let loc, layout = letModuleBinding s me in
              processLetList ((loc, layout) :: acc) e
            | [], Pexp_letexception (extensionConstructor, expr) ->
              let exc = self#exception_declaration extensionConstructor in
              let layout = source_map ~loc:extensionConstructor.pext_loc exc in
              processLetList
                ((extensionConstructor.pext_loc, layout) :: acc)
                expr
            | [], Pexp_sequence (({ pexp_desc = Pexp_sequence _; _ } as e1), e2)
            | [], Pexp_sequence (({ pexp_desc = Pexp_let _; _ } as e1), e2)
            | [], Pexp_sequence (({ pexp_desc = Pexp_open _; _ } as e1), e2)
            | [], Pexp_sequence (({ pexp_desc = Pexp_letmodule _; _ } as e1), e2)
            | [], Pexp_sequence (e1, e2) ->
              let e1Layout =
                match expression_not_immediate_extension_sugar e1 with
                | Some (extension, e) ->
                  self#attach_std_item_attrs ~extension [] (self#unparseExpr e)
                | None -> self#unparseExpr e1
              in
              let loc = e1.pexp_loc in
              let layout = source_map ~loc e1Layout in
              processLetList ((loc, layout) :: acc) e2
            | _ ->
              let expr =
                { expr with pexp_attributes = arityAttrs @ stdAttrs @ jsxAttrs }
              in
              (match expression_not_immediate_extension_sugar expr with
              | Some
                  ( extension
                  , { pexp_attributes = []; pexp_desc = Pexp_let (rf, l, e); _ }
                  ) ->
                let bindingsLayout = self#bindings ~extension (rf, l) in
                let bindingsLoc =
                  self#bindingsLocationRange ~extension:expr l
                in
                let layout = source_map ~loc:bindingsLoc bindingsLayout in
                processLetList
                  ((extractLocationFromValBindList expr l, layout) :: acc)
                  e
              | Some
                  ( extension
                  , { pexp_attributes = []
                    ; pexp_desc = Pexp_letmodule (s, me, e)
                    ; _
                    } ) ->
                let loc, layout = letModuleBinding ~extension s me in
                processLetList ((loc, layout) :: acc) e
              | Some
                  ( extension
                  , { pexp_attributes = attrs
                    ; pexp_desc = Pexp_open (me, e)
                    ; _
                    } ) ->
                let loc, layout = self#pexp_open ~attrs ~extension expr me in
                processLetList ((loc, layout) :: acc) e
              | Some (extension, e) ->
                let layout =
                  self#attach_std_item_attrs ~extension [] (self#unparseExpr e)
                in
                (expr.pexp_loc, layout) :: acc
              | None ->
                (* Should really do something to prevent infinite loops here.
                   Never allowing a top level call into letList to recurse back
                   to self#unparseExpr- top level calls into letList *must* be
                   one of the special forms above whereas lower level recursive
                   calls may be of any form. *)
                let layout =
                  source_map ~loc:expr.pexp_loc (self#unparseExpr expr)
                in
                (expr.pexp_loc, layout) :: acc)
          in
          let es = processLetList [] expr in
          (* Interleave whitespace between the "let-items" when appropriate *)
          groupAndPrint
            ~xf:(fun (_, layout) -> layout)
            ~getLoc:(fun (loc, _) -> loc)
            ~comments:self#comments
            (List.rev es)

        method constructor_expression
          ?(polyVariant = false)
          ~arityIsClear
          stdAttrs
          ctor
          eo =
          let implicit_arity, arguments =
            match eo.pexp_desc with
            | Pexp_construct ({ txt = Lident "()"; _ }, _) ->
              (* `foo() is a polymorphic variant that contains a single unit construct as expression
               * This requires special formatting: `foo(()) -> `foo() *)
              false, atom "()"
            (* special printing: MyConstructor(()) -> MyConstructor() *)
            | Pexp_tuple l when is_single_unit_construct l -> false, atom "()"
            | Pexp_tuple l when polyVariant == true ->
              false, self#unparseSequence ~wrap:("(", ")") ~construct:`Tuple l
            | Pexp_tuple l ->
              (* There is no ambiguity when the number of tuple components is 1.
                 We don't need put implicit_arity in that case *)
              (match l with
              | exprList when isSingleArgParenApplication exprList ->
                false, self#singleArgParenApplication exprList
              | _ ->
                not arityIsClear, makeTup (List.map self#unparseProtectedExpr l))
            | _ when isSingleArgParenApplication [ eo ] ->
              false, self#singleArgParenApplication [ eo ]
            | _ -> false, makeTup [ self#unparseProtectedExpr eo ]
          in
          let arguments = source_map ~loc:eo.pexp_loc arguments in
          let construction =
            label
              ctor
              (if isSequencey arguments
               then arguments
               else ensureSingleTokenSticksToLabel arguments)
          in
          let attrs =
            if implicit_arity && not polyVariant
            then
              { attr_name = { txt = "implicit_arity"; loc = eo.pexp_loc }
              ; attr_payload = PStr []
              ; attr_loc = eo.pexp_loc
              }
              :: stdAttrs
            else stdAttrs
          in
          match attrs with
          | [] -> construction
          | _ :: _ -> formatAttributed construction (self#attributes attrs)

        (* TODOATTRIBUTES: Handle stdAttrs here (merge with implicit_arity) *)
        method constructor_pattern ?(polyVariant = false) ~arityIsClear ctor po
            =
          let implicit_arity, arguments =
            match po.ppat_desc with
            (* There is no ambiguity when the number of tuple components is 1.
               We don't need put implicit_arity in that case *)
            | Ppat_tuple (([] | _ :: []) as l) -> false, l
            | Ppat_tuple l -> not arityIsClear, l
            | _ -> false, [ po ]
          in
          let space, arguments =
            match arguments with
            | [ x ] when is_direct_pattern x -> true, self#simple_pattern x
            | xs when isSingleArgParenPattern xs ->
              false, self#singleArgParenPattern xs
            (* Optimize the case when it's a variant holding a shot variable -
               avoid trailing*)
            | [ ({ ppat_desc = Ppat_constant (Pconst_string (s, _, None)); _ }
                 as x)
              ]
            | [ ({ ppat_desc = Ppat_construct ({ txt = Lident s; _ }, None); _ }
                 as x)
              ]
            | [ ({ ppat_desc = Ppat_var { txt = s; _ }; _ } as x) ]
              when Reason_heuristics.singleTokenPatternOmmitTrail s ->
              let layout = makeTup ~trailComma:false [ self#pattern x ] in
              false, source_map ~loc:po.ppat_loc layout
            | [ ({ ppat_desc = Ppat_any; _ } as x) ]
            | [ ({ ppat_desc = Ppat_constant (Pconst_char _); _ } as x) ]
            | [ ({ ppat_desc = Ppat_constant (Pconst_integer _); _ } as x) ] ->
              let layout = makeTup ~trailComma:false [ self#pattern x ] in
              false, source_map ~loc:po.ppat_loc layout
            | xs ->
              let layout = makeTup (List.map self#pattern xs) in
              false, source_map ~loc:po.ppat_loc layout
          in
          let construction = label ~space ctor arguments in
          if implicit_arity && not polyVariant
          then
            formatAttributed
              construction
              (self#attributes
                 [ { attr_name = { txt = "implicit_arity"; loc = po.ppat_loc }
                   ; attr_payload = PStr []
                   ; attr_loc = po.ppat_loc
                   }
                 ])
          else construction

        (* Provides special printing for constructor arguments:
         * iff there's one argument & they have some kind of wrapping,
         * they're wrapping need to 'hug' the surrounding parens.
         * Example:
         *  switch x {
         *  | Some({
         *      a,
         *      b,
         *    }) => ()
         *  }
         *
         *  Notice how ({ and }) hug.
         *  This applies for records, arrays, tuples & lists.
         *  Also see `isSingleArgParenPattern` to determine if this kind of wrapping applies.
        *)
        method singleArgParenPattern =
          function
          | [ { ppat_desc = Ppat_record (l, closed); ppat_loc = loc; _ } ] ->
            source_map ~loc (self#patternRecord ~wrap:("(", ")") l closed)
          | [ { ppat_desc = Ppat_array l; ppat_loc = loc; _ } ] ->
            source_map ~loc (self#patternArray ~wrap:("(", ")") l)
          | [ { ppat_desc = Ppat_tuple l; ppat_loc = loc; _ } ] ->
            source_map ~loc (self#patternTuple ~wrap:("(", ")") l)
          | [ ({ ppat_desc = Ppat_construct ({ txt = Lident "::"; _ }, _)
               ; ppat_loc
               ; _
               } as listPattern)
            ] ->
            source_map
              ~loc:ppat_loc
              (self#patternList ~wrap:("(", ")") listPattern)
          | _ -> assert false

        (* TODO: Similar to tuples, do not print parens around type constraints
           (same for lists) *)
        method patternArray ?(wrap = "", "") l =
          let left, right = wrap in
          let wrap = left ^ "[|", "|]" ^ right in
          makeList
            ~wrap
            ~break:IfNeed
            ~postSpace:true
            ~sep:commaTrail
            (List.map self#pattern l)

        method patternTuple ?(wrap = "", "") l =
          let left, right = wrap in
          let wrap = left ^ "(", ")" ^ right in
          makeList
            ~wrap
            ~sep:commaTrail
            ~postSpace:true
            ~break:IfNeed
            (List.map self#pattern l)

        method patternRecord ?(wrap = "", "") l closed =
          let longident_x_pattern (li, p) =
            match li, p.ppat_desc with
            | { txt = ident; _ }, Ppat_var { txt; _ }
              when Longident.last_exn ident = txt ->
              (* record field punning when destructuring. {x: x, y: y} becomes {x, y} *)
              (* works with module prefix too: {MyModule.x: x, y: y} becomes {MyModule.x, y} *)
              self#longident_loc li
            | ( { txt = ident; _ }
              , Ppat_alias
                  ( { ppat_desc = Ppat_var { txt = ident2; _ }; _ }
                  , { txt = aliasIdent; _ } ) )
              when Longident.last_exn ident = ident2 ->
              (* record field punning when destructuring with renaming. {state:
                 state as prevState} becomes {state as prevState *)
              (* works with module prefix too: {ReasonReact.state: state as
                 prevState} becomes {ReasonReact.state as prevState *)
              makeList
                ~sep:(Sep " ")
                [ self#longident_loc li; atom "as"; atom aliasIdent ]
            | _ ->
              let pattern =
                let formatted = self#pattern p in
                let wrap =
                  match p.ppat_desc with
                  | Ppat_constraint (_, _) -> Some ("(", ")")
                  | _ -> None
                in
                makeList ~inline:(true, true) ?wrap [ formatted ]
              in
              label
                ~space:true
                (makeList [ self#longident_loc li; atom ":" ])
                pattern
          in
          let rows =
            List.map longident_x_pattern l
            @ match closed with Closed -> [] | _ -> [ atom "_" ]
          in
          let left, right = wrap in
          let wrap = left ^ "{", "}" ^ right in
          makeList ~wrap ~break:IfNeed ~sep:commaTrail ~postSpace:true rows

        method patternFunction ?extension loc l =
          let estimatedFunLocation =
            { loc_start = loc.loc_start
            ; loc_end =
                { loc.loc_start with
                  pos_cnum = loc.loc_start.Lexing.pos_cnum + 3
                }
            ; loc_ghost = false
            }
          in
          makeList
            ~postSpace:true
            ~break:IfNeed
            ~inline:(true, true)
            ~pad:(false, false)
            (atom
               ~loc:estimatedFunLocation
               (add_extension_sugar funToken extension)
            :: self#case_list l)

        method parenthesized_expr ?break expr =
          let result = self#unparseExpr expr in
          match expr.pexp_attributes, expr.pexp_desc with
          | [], (Pexp_tuple _ | Pexp_construct ({ txt = Lident "()"; _ }, None))
            ->
            result
          | _ -> makeList ~wrap:("(", ")") ?break [ self#unparseExpr expr ]

        (* Expressions requiring parens, in most contexts such as separated by
           infix *)
        method expression_requiring_parens_in_infix x =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.pexp_attributes
          in
          assert (stdAttrs == []);
          (* keep the incoming expression around, an expr with
           * immediate extension sugar might contain less than perfect location
           * info in its children (used for comment interleaving), the expression passed to
           * 'expression_requiring_parens_in_infix' contains the correct location *)
          let originalExpr = x in
          let extension, x = expression_immediate_extension_sugar x in
          match x.pexp_desc with
          (* The only reason Pexp_fun must also be wrapped in parens when under
             pipe, is that its => token will be confused with the match token.
             Simple expression will also invoke `#reset`. *)
          | Pexp_function _ when pipe || semi ->
            None (* Would be rendered as simplest_expression *)
          (* Pexp_function, on the other hand, doesn't need wrapping in parens
             in most cases anymore, since `fun` is not ambiguous anymore (we
             print Pexp_fun as ES6 functions). *)
          | Pexp_function l ->
            let prec = Custom funToken in
            let expr = self#patternFunction ?extension x.pexp_loc l in
            Some
              (SpecificInfixPrecedence
                 ( { reducePrecedence = prec; shiftPrecedence = prec }
                 , LayoutNode expr ))
          | _ ->
            (* The Pexp_function cases above don't use location because comment
               printing breaks for them. *)
            let itm =
              match x.pexp_desc with
              | Pexp_fun _ | Pexp_newtype _ ->
                (* let uncurried = *)
                let args, ret = self#curriedPatternsAndReturnVal x in
                (match args with
                | [] -> raise (NotPossible "no arrow args in unparse ")
                | firstArg :: tl ->
                  (* Suboptimal printing of parens:
                   *
                   *    something >>= fun x => x + 1;
                   *
                   * Will be printed as:
                   *
                   *    something >>= (fun x => x + 1);
                   *
                   * Because the arrow has lower precedence than >>=, but it wasn't
                   * needed because
                   *
                   *    (something >>= fun x) => x + 1;
                   *
                   * Is not a valid parse. Parens around the `=>` weren't needed to
                   * prevent reducing instead of shifting. To optimize this part, we need
                   * a much deeper encoding of the parse rules to print parens only when
                   * needed, testing which rules will be reduced. It really should be
                   * integrated deeply with Menhir.
                   *
                   * One question is, if it's this difficult to describe when parens are
                   * needed, should we even print them with the minimum amount?  We can
                   * instead model everything as "infix" with ranked precedences.
                  *)
                  let retValUnparsed = self#unparseExprApplicationItems ret in
                  Some
                    (self#wrapCurriedFunctionBinding
                       ~sweet:(extension = None)
                       (add_extension_sugar funToken extension)
                       ~arrow:"=>"
                       firstArg
                       tl
                       retValUnparsed))
              | Pexp_try (e, l) ->
                let estimatedBracePoint =
                  { loc_start = e.pexp_loc.loc_end
                  ; loc_end = x.pexp_loc.loc_end
                  ; loc_ghost = false
                  }
                in
                let cases =
                  self#case_list ~allowUnguardedSequenceBodies:true l
                in
                let switchWith =
                  self#dont_preserve_braces#formatSingleArgLabelApplication
                    (atom (add_extension_sugar "try" extension))
                    e
                in
                Some
                  (label
                     ~space:true
                     switchWith
                     (source_map
                        ~loc:estimatedBracePoint
                        (makeList
                           ~indent:settings.trySwitchIndent
                           ~wrap:("{", "}")
                           ~break:Always_rec
                           ~postSpace:true
                           cases)))
              (* These should have already been handled and we should never
                 havgotten this far. *)
              | Pexp_setinstvar _ ->
                raise
                  (Invalid_argument
                     "Cannot handle setinstvar here - call unparseExpr")
              | Pexp_setfield (_, _, _) ->
                raise
                  (Invalid_argument
                     "Cannot handle setfield here - call unparseExpr")
              | Pexp_apply _ ->
                raise
                  (Invalid_argument
                     "Cannot handle apply here - call unparseExpr")
              | Pexp_match (e, l) ->
                let estimatedBracePoint =
                  { loc_start = e.pexp_loc.loc_end
                  ; (* See originalExpr binding, for more info.
                     * It contains the correct location under immediate extension sugar *)
                    loc_end = originalExpr.pexp_loc.loc_end
                  ; loc_ghost = false
                  }
                in
                let cases =
                  self#case_list ~allowUnguardedSequenceBodies:true l
                in
                let switchWith =
                  label
                    ~space:true
                    (atom (add_extension_sugar "switch" extension))
                    (self#parenthesized_expr ~break:IfNeed e)
                in
                let lbl =
                  label
                    ~space:true
                    switchWith
                    (source_map
                       ~loc:estimatedBracePoint
                       (makeList
                          ~indent:settings.trySwitchIndent
                          ~wrap:("{", "}")
                          ~break:Always_rec
                          ~postSpace:true
                          cases))
                in
                Some lbl
              | Pexp_ifthenelse (e1, e2, eo) ->
                let blocks, finalExpression = sequentialIfBlocks eo in
                let rec singleExpression exp =
                  match exp.pexp_desc with
                  | Pexp_ident _ -> true
                  | Pexp_constant _ -> true
                  | Pexp_construct (_, arg) ->
                    (match arg with
                    | None -> true
                    | Some x -> singleExpression x)
                  | _ -> false
                in
                let singleLineIf =
                  singleExpression e1
                  && singleExpression e2
                  &&
                  match eo with
                  | Some expr -> singleExpression expr
                  | None -> true
                in
                let makeLetSequence =
                  if singleLineIf
                  then makeLetSequenceSingleLine
                  else makeLetSequence
                in
                let rec sequence soFar remaining =
                  match remaining, finalExpression with
                  | [], None -> soFar
                  | [], Some e ->
                    let soFarWithElseAppended =
                      makeList ~postSpace:true [ soFar; atom "else" ]
                    in
                    label
                      ~space:true
                      soFarWithElseAppended
                      (source_map
                         ~loc:e.pexp_loc
                         (makeLetSequence (self#letList e)))
                  | hd :: tl, _ ->
                    let e1, e2 = hd in
                    let soFarWithElseIfAppended =
                      label
                        ~space:true
                        (makeList ~postSpace:true [ soFar; atom "else if" ])
                        (makeList ~wrap:("(", ")") [ self#unparseExpr e1 ])
                    in
                    let nextSoFar =
                      label
                        ~space:true
                        soFarWithElseIfAppended
                        (source_map
                           ~loc:e2.pexp_loc
                           (makeLetSequence (self#letList e2)))
                    in
                    sequence nextSoFar tl
                in
                let init =
                  let if_ = atom (add_extension_sugar "if" extension) in
                  let cond = self#parenthesized_expr e1 in
                  label
                    ~space:true
                    (source_map ~loc:e1.pexp_loc (label ~space:true if_ cond))
                    (source_map
                       ~loc:e2.pexp_loc
                       (makeLetSequence (self#letList e2)))
                in
                Some (sequence init blocks)
              | Pexp_while (e1, e2) ->
                let lbl =
                  let while_ = atom (add_extension_sugar "while" extension) in
                  let cond = self#parenthesized_expr e1 in
                  label
                    ~space:true
                    (label ~space:true while_ cond)
                    (source_map
                       ~loc:e2.pexp_loc
                       (makeLetSequence (self#letList e2)))
                in
                Some lbl
              | Pexp_for (s, e1, e2, df, e3) ->
                (*  for longIdentifier in
                 *      (longInit expr) to
                 *      (longEnd expr) {
                 *    print_int longIdentifier;
                 *  };
                *)
                let identifierIn =
                  makeList ~postSpace:true [ self#pattern s; atom "in" ]
                in
                let dockedToFor =
                  makeList
                    ~break:IfNeed
                    ~postSpace:true
                    ~inline:(true, true)
                    ~wrap:("(", ")")
                    [ identifierIn
                    ; makeList
                        ~postSpace:true
                        [ self#unparseExpr e1; self#direction_flag df ]
                    ; self#unparseExpr e2
                    ]
                in
                let upToBody =
                  makeList
                    ~inline:(true, true)
                    ~postSpace:true
                    [ atom (add_extension_sugar "for" extension); dockedToFor ]
                in
                Some
                  (label
                     ~space:true
                     upToBody
                     (source_map
                        ~loc:e3.pexp_loc
                        (makeLetSequence (self#letList e3))))
              | Pexp_new li ->
                Some
                  (label
                     ~space:true
                     (atom "new")
                     (self#longident_class_or_type_loc li))
              | Pexp_assert e ->
                Some (label (atom "assert") (makeTup [ self#unparseExpr e ]))
              | Pexp_lazy e ->
                Some (self#formatSingleArgLabelApplication (atom "lazy") e)
              | Pexp_poly _ ->
                failwith
                  ("This version of the pretty printer assumes it is \
                    impossible to "
                  ^ "construct a Pexp_poly outside of a method definition - \
                     yet it sees one.")
              | _ -> None
            in
            (match itm with
            | None -> None
            | Some i ->
              Some (PotentiallyLowPrecedence (source_map ~loc:x.pexp_loc i)))

        method potentiallyConstrainedExpr x =
          match x.pexp_desc with
          | Pexp_constraint (e, ct) ->
            formatTypeConstraint (self#unparseExpr e) (self#core_type ct)
          | _ -> self#unparseExpr x

        (* Because the rule BANG simple_expr was given %prec below_DOT_AND_SHARP,
         * !x.y.z will parse as !(x.y.z) and not (!x).y.z.
         *
         *     !x.y.z == !((x.y).z)
         *     !x#y#z == !((x#y)#z)
         *
         * So the intuition is: In general, any simple expression can exist to the
         * left of a `.`, except `BANG simple_expr`, which has special precedence,
         * and must be guarded in this one case.
         *
         * TODO: Instead of special casing this here, we should continue to extend
         * unparseExpr to also unparse simple expressions, (by encoding the
         * rules precedence below_DOT_AND_SHARP).
         *
         * TODO:
         *  Some would even have the prefix application be parsed with lower
         *  precedence function *application*. In the case of !, where ! means not,
         *  it makes a lot of sense because (!identifier)(arg) would be meaningless.
         *
         *  !callTheFunction(1, 2, 3)(andEvenCurriedArgs)
         *
         * Only problem is that it could then not appear anywhere simple expressions
         * would appear.
         *
         * We could make a special case for ! followed by one simple expression, and
         * consider the result simple.
         *
         * Alternatively, we can figure out a way to not require simple expressions
         * in the most common locations such as if/while tests. This is really hard
         * (impossible w/ grammars Menhir supports?)
         *
         * if ! myFunc argOne argTwo {
         *
         * } else {
         *
         * };
         *
        *)
        method simple_enough_to_be_lhs_dot_send x =
          match x.pexp_desc with
          | Pexp_apply (eFun, _) ->
            (match printedStringAndFixityExpr eFun with
            | AlmostSimplePrefix _ | UnaryPlusPrefix _ | UnaryMinusPrefix _
            | UnaryNotPrefix _ | UnaryPostfix _ | Infix _ ->
              self#simplifyUnparseExpr x
            | Letop _ | Andop _ | Normal ->
              if x.pexp_attributes == []
              then
                (* `let a = foo().bar` instead of `let a = (foo()).bar *)
                (* same for foo()##bar, foo()#=bar, etc. *)
                self#unparseExpr x
              else self#simplifyUnparseExpr x)
          | _ -> self#simplifyUnparseExpr x

        method unparseRecord
          ?wrap:(lwrap, rwrap = "", "")
          ?(withStringKeys = false)
          ?(allowPunning = true)
          ?(forceBreak = false)
          l
          eo =
          (* forceBreak is a ref which can be set to always break the record rows.
           * Example, when we have a row which contains a nested record,
           * this ref can be set to true from inside the printing of that row,
           * which forces breaks for the outer record structure. *)
          let forceBreak = ref forceBreak in
          let quote = atom "\"" in
          let maybeQuoteFirstElem fst rest =
            if withStringKeys
            then
              match fst.txt with
              | Lident s -> quote :: atom s :: quote :: rest
              | Ldot _ | Lapply _ -> assert false
            else self#longident_loc fst :: rest
          in
          let makeRow (li, e) shouldPun =
            let totalRowLoc =
              { loc_start = li.Asttypes.loc.loc_start
              ; loc_end = e.pexp_loc.loc_end
              ; loc_ghost = false
              }
            in
            let theRow =
              match e.pexp_desc, shouldPun, allowPunning with
              (* record value punning. Turns {foo: foo, bar: 1} into {foo, bar: 1} *)
              (* also turns {Foo.bar: bar, baz: 1} into {Foo.bar, baz: 1} *)
              (* don't turn {bar: Foo.bar, baz: 1} into {bar, baz: 1}, naturally *)
              | Pexp_ident { txt = Lident value; _ }, true, true
                when Longident.last_exn li.txt = value ->
                makeList (maybeQuoteFirstElem li [])
                (* Force breaks for nested records or mel.obj sugar
                 * Example:
                 *  let person = {name: {first: "Bob", last: "Zhmith"}, age: 32};
                 * is a lot less readable than
                 *  let person = {
                 *   "name": {
                 *     "first": "Bob",
                 *     "last": "Zhmith"
                 *   },
                 *  "age": 32
                 *  };
                *)
              | Pexp_record (recordRows, optionalGadt), _, _ ->
                forceBreak := true;
                let keyWithColon =
                  makeList (maybeQuoteFirstElem li [ atom ":" ])
                in
                let value =
                  self#unparseRecord ~forceBreak:true recordRows optionalGadt
                in
                label ~space:true keyWithColon value
              | Pexp_extension (s, p), _, _ when s.txt = "mel.obj" ->
                forceBreak := true;
                let keyWithColon =
                  makeList (maybeQuoteFirstElem li [ atom ":" ])
                in
                let value = self#formatBsObjExtensionSugar ~forceBreak:true p in
                label ~space:true keyWithColon value
              | Pexp_object classStructure, _, _ ->
                forceBreak := true;
                let keyWithColon =
                  makeList (maybeQuoteFirstElem li [ atom ":" ])
                in
                let value =
                  self#classStructure ~forceBreak:true classStructure
                in
                label ~space:true keyWithColon value
              | _ ->
                let argsList, return = self#curriedPatternsAndReturnVal e in
                (match argsList with
                | [] ->
                  let appTerms = self#unparseExprApplicationItems e in
                  let upToColon =
                    makeList (maybeQuoteFirstElem li [ atom ":" ])
                  in
                  formatAttachmentApplication
                    applicationFinalWrapping
                    (Some (true, upToColon))
                    appTerms
                | firstArg :: tl ->
                  let upToColon =
                    makeList (maybeQuoteFirstElem li [ atom ":" ])
                  in
                  let returnedAppTerms =
                    self#unparseExprApplicationItems return
                  in
                  self#wrapCurriedFunctionBinding
                    ~sweet:true
                    ~attachTo:upToColon
                    funToken
                    ~arrow:"=>"
                    firstArg
                    tl
                    returnedAppTerms)
            in
            source_map ~loc:totalRowLoc theRow, totalRowLoc
          in
          let rec getRows l =
            match l with
            | [] -> []
            | hd :: [] -> [ makeRow hd true ]
            | hd :: hd2 :: tl -> makeRow hd true :: getRows (hd2 :: tl)
          in

          let allRows =
            match eo with
            | None ->
              (match l with
              (* No punning (or comma) for records with only a single field.
                 It's ambiguous with an expression in a scope *)
              (* See comment in parser.mly for
                 lbl_expr_list_with_at_least_one_non_punned_field *)
              | [ hd ] -> [ makeRow hd false ]
              | _ -> getRows l)
            (* This case represents a "spread" being present -> {...x, a: 1, b:
               2} *)
            | Some withRecord ->
              let firstRow =
                let row =
                  (* Unclear why "sugar_expr" was special cased hre. *)
                  let appTerms = self#unparseExprApplicationItems withRecord in
                  formatAttachmentApplication
                    applicationFinalWrapping
                    (Some (false, atom "..."))
                    appTerms
                in
                source_map ~loc:withRecord.pexp_loc row, withRecord.pexp_loc
              in
              firstRow :: getRows l
          in
          let break =
            (* if a record has more than 1 row, always break *)
            match !forceBreak, allRows with
            | false, ([] | [ _ ]) -> Layout.IfNeed
            | _ -> Layout.Always_rec
          in
          makeList
            ~wrap:(lwrap ^ "{", "}" ^ rwrap)
            ~break
            ~sep:commaTrail
            ~postSpace:true
            (groupAndPrint ~xf:fst ~getLoc:snd ~comments:self#comments allRows)

        method isSeriesOfOpensFollowedByNonSequencyExpression expr =
          match expr.pexp_attributes, expr.pexp_desc with
          | [], Pexp_let _ -> false
          | [], Pexp_letop _ -> false
          | [], Pexp_sequence _ -> false
          | [], Pexp_letmodule _ -> false
          | ( []
            , Pexp_open
                ( { popen_override
                  ; popen_expr = { pmod_desc = Pmod_ident _; _ }
                  ; _
                  }
                , e ) ) ->
            popen_override == Fresh
            && self#isSeriesOfOpensFollowedByNonSequencyExpression e
          | [], Pexp_open _ -> false
          | [], Pexp_letexception _ -> false
          | [], Pexp_extension ({ txt; _ }, _) -> txt = "mel.obj"
          | _ -> true

        method unparseObject
          ?wrap:(lwrap, rwrap = "", "")
          ?(withStringKeys = false)
          l
          o =
          let core_field_type { pof_desc; pof_attributes; _ } =
            match pof_desc with
            | Otag ({ txt; _ }, ct) ->
              let l = Reason_attributes.extractStdAttrs pof_attributes in
              let row =
                let rowKey =
                  if withStringKeys
                  then makeList ~wrap:("\"", "\"") [ atom txt ]
                  else atom txt
                in
                label
                  ~space:true
                  (makeList ~break:Layout.Never [ rowKey; atom ":" ])
                  (self#core_type ct)
              in
              (match l with
              | [] -> row
              | _ :: _ ->
                makeList
                  ~postSpace:true
                  ~break:IfNeed
                  ~inline:(true, true)
                  (List.concat [ self#attributes pof_attributes; [ row ] ]))
            | Oinherit ct ->
              makeList ~break:Layout.Never [ atom "..."; self#core_type ct ]
          in
          let rows = List.map core_field_type l in
          let openness =
            match o with Closed -> atom "." | Open -> atom ".."
          in
          (* if an object has more than 2 rows, always break for readability *)
          let rows_layout =
            let break =
              match rows with
              | [] | [ _ ] -> Layout.IfNeed
              | _ -> Layout.Always_rec
            in
            makeList
              ~break
              ~inline:(true, true)
              ~postSpace:true
              ~sep:commaTrail
              rows
          in
          makeList
            ~break:Layout.IfNeed
            ~preSpace:(rows != [])
            ~wrap:(lwrap ^ "{", "}" ^ rwrap)
            (openness :: [ rows_layout ])

        method unparseSequence ?(wrap = "", "") ~construct l =
          match construct with
          | `ES6List ->
            let seq, ext =
              match List.rev l with
              | ext :: seq_rev -> List.rev seq_rev, ext
              | [] -> assert false
            in
            makeES6List
              ~wrap
              (List.map self#unparseExpr seq)
              (self#unparseExpr ext)
          | _ ->
            let left, right = wrap in
            let xf, (leftDelim, rightDelim) =
              match construct with
              | `List -> self#unparseExpr, ("[", "]")
              | `Array -> self#unparseExpr, ("[|", "|]")
              | `Tuple -> self#potentiallyConstrainedExpr, ("(", ")")
              | `ES6List -> assert false
            in
            let wrap = left ^ leftDelim, rightDelim ^ right in
            makeList
              ~wrap
              ~sep:commaTrail
              ~break:IfNeed
              ~postSpace:true
              (List.map xf l)

        method formatBsObjExtensionSugar
          ?(wrap = "", "")
          ?(forceBreak = false)
          payload =
          match payload with
          | PStr [ itm ] ->
            (match itm with
            | { pstr_desc =
                  Pstr_eval ({ pexp_desc = Pexp_record (l, eo); _ }, [])
              ; _
              } ->
              self#unparseRecord
                ~forceBreak
                ~wrap
                ~withStringKeys:true
                ~allowPunning:false
                l
                eo
            | { pstr_desc =
                  Pstr_eval
                    ( { pexp_desc =
                          Pexp_extension ({ txt = "mel.obj"; _ }, payload)
                      ; _
                      }
                    , [] )
              ; _
              } ->
              (* some folks write `[%mel.obj [%mel.obj {foo: bar}]]`. This looks
                 improbable but it happens often if you use the sugared version:
                 `[%mel.obj {"foo": bar}]`. We're gonna be lenient here and
                 treat it as if they wanted to just write `{"foo": bar}`.
                 BuckleScript does the same relaxation when parsing mel.obj *)
              self#formatBsObjExtensionSugar ~wrap ~forceBreak payload
            | _ ->
              raise
                (Invalid_argument
                   "mel.obj only accepts a record. You've passed something else"))
          | _ -> assert false

        method should_preserve_requested_braces expr =
          let { Reason_attributes.stylisticAttrs; _ } =
            Reason_attributes.partitionAttributes expr.pexp_attributes
          in
          match expr.pexp_desc with
          | Pexp_ifthenelse _ | Pexp_try _ -> false
          | Pexp_sequence _ ->
            (* `let ... in` should _always_ preserve braces *)
            true
          | _ ->
            preserve_braces
            && Reason_attributes.has_preserve_braces_attrs stylisticAttrs

        method simplest_expression x =
          let { Reason_attributes.stdAttrs
              ; jsxAttrs
              ; stylisticAttrs
              ; arityAttrs
              ; _
              }
            =
            Reason_attributes.partitionAttributes x.pexp_attributes
          in
          let hasJsxAttribute = jsxAttrs != [] in
          if stdAttrs != []
          then None
          else if self#should_preserve_requested_braces x
          then
            let layout =
              makeList
                ~break:(if inline_braces then Always else Always_rec)
                ~inline:(true, inline_braces)
                ~wrap:("{", "}")
                ~postSpace:true
                ~sep:(if inline_braces then Sep ";" else SepFinal (";", ";"))
                (self#letList x)
            in
            Some layout
          else
            let item =
              match x.pexp_desc with
              (* The only reason Pexp_fun must also be wrapped in parens is that
                 its => token will be confused with the match token. *)
              | Pexp_fun _ when pipe || semi ->
                Some (self#reset#simplifyUnparseExpr x)
              | Pexp_function l when pipe || semi ->
                Some
                  (formatPrecedence
                     ~loc:x.pexp_loc
                     (self#reset#patternFunction x.pexp_loc l))
              | Pexp_apply _ ->
                (match self#simple_get_application x with
                (* If it's the simple form of application. *)
                | Some simpleGet -> Some simpleGet
                | None -> None)
              | Pexp_object cs -> Some (self#classStructure cs)
              | Pexp_override l ->
                (* FIXME *)
                let string_x_expression (s, e) =
                  label ~space:true (atom (s.txt ^ ":")) (self#unparseExpr e)
                in
                Some
                  (makeList
                     ~postSpace:true
                     ~wrap:("{<", ">}")
                     ~sep:(Sep ",")
                     (List.map string_x_expression l))
              | Pexp_construct ({ txt = Lident "[]"; _ }, _)
                when hasJsxAttribute ->
                Some (atom "<> </>")
              | Pexp_construct ({ txt = Lident "::"; _ }, Some _)
                when hasJsxAttribute ->
                (match self#formatJsxChildrenNonSpread x [] with
                | None ->
                  (* Back out of the standard jsx child formatting *)
                  (* This is actually not a useful construct to have written:
                   *   <> ... x </>
                   * Is the same as:
                   *   x
                   * There is also a bug in the parser where a space is needed
                   * between <> and ..., but no one would write the ... form of
                   * <> anyways. *)
                  let withoutJsxAttributes =
                    { x with pexp_attributes = stylisticAttrs @ arityAttrs }
                  in
                  self#simplest_expression withoutJsxAttributes
                | Some chldn ->
                  Some
                    (makeList
                       ~break:IfNeed
                       ~inline:(false, false)
                       ~postSpace:true
                       ~wrap:("<>", "</>")
                       ~pad:(true, true)
                       chldn))
              | Pexp_construct _ when is_simple_construct (view_expr x) ->
                Some
                  (match view_expr x with
                  | `nil -> atom "[]"
                  | `tuple -> atom "()"
                  | `list xs ->
                    (* LIST EXPRESSION *)
                    self#unparseSequence ~construct:`List xs
                  | `cons xs -> self#unparseSequence ~construct:`ES6List xs
                  | `simple x -> self#longident x
                  | _ -> assert false)
              | Pexp_ident li ->
                (* Lone identifiers shouldn't break when to the right of a
                   label *)
                Some (ensureSingleTokenSticksToLabel (self#longident_loc li))
              | Pexp_constant c ->
                (* Constants shouldn't break when to the right of a label *)
                let raw_literal, _ =
                  Reason_attributes.extract_raw_literal x.pexp_attributes
                in
                Some
                  (ensureSingleTokenSticksToLabel
                     (self#constant ?raw_literal c))
              | Pexp_pack me ->
                Some
                  (makeList
                     ~break:IfNeed
                     ~postSpace:true
                     ~wrap:("(", ")")
                     ~inline:(true, true)
                     [ atom "module"; self#module_expr me ])
              | Pexp_tuple l ->
                (* TODO: These may be simple, non-simple, or type constrained
                   non-simple expressions *)
                Some (self#unparseSequence ~construct:`Tuple l)
              | Pexp_constraint (e, ct) ->
                Some
                  (makeList
                     ~break:IfNeed
                     ~wrap:("(", ")")
                     [ formatTypeConstraint
                         (self#unparseExpr e)
                         (self#core_type ct)
                     ])
              | Pexp_coerce (e, cto1, ct) ->
                let optFormattedType =
                  match cto1 with
                  | None -> None
                  | Some typ -> Some (self#core_type typ)
                in
                Some
                  (makeList
                     ~break:IfNeed
                     ~wrap:("(", ")")
                     [ formatCoerce
                         (self#unparseExpr e)
                         optFormattedType
                         (self#core_type ct)
                     ])
              | Pexp_variant (l, None) ->
                Some (ensureSingleTokenSticksToLabel (atom ("`" ^ l)))
              | Pexp_record (l, eo) -> Some (self#unparseRecord l eo)
              | Pexp_array l -> Some (self#unparseSequence ~construct:`Array l)
              | Pexp_let _ | Pexp_sequence _ | Pexp_letmodule _
              | Pexp_letexception _ | Pexp_letop _ ->
                Some (makeLetSequence (self#letList x))
              | Pexp_extension e ->
                (match expression_immediate_extension_sugar x with
                | Some _, _ -> None
                | None, _ ->
                  (match expression_extension_sugar x with
                  | None -> Some (self#extension e)
                  | Some (ext, x') ->
                    (match x'.pexp_desc with
                    | Pexp_let _ | Pexp_letop _ | Pexp_letmodule _ ->
                      Some (makeLetSequence (self#letList x))
                    | Pexp_constant (Pconst_string (i, _, Some delim)) ->
                      let { Reason_attributes.stylisticAttrs; _ } =
                        Reason_attributes.partitionAttributes
                          ~allowUncurry:
                            (Reason_heuristics.bsExprCanBeUncurried x')
                          x'.pexp_attributes
                      in
                      if
                        Reason_attributes.has_quoted_extension_attrs
                          stylisticAttrs
                      then Some (quoted_ext ext i delim)
                      else Some (self#extension e)
                    | _ -> Some (self#extension e))))
              | Pexp_open (me, e) ->
                if self#isSeriesOfOpensFollowedByNonSequencyExpression x
                then
                  Some
                    (label
                       (label
                          (self#moduleExpressionToFormattedApplicationItems
                             me.popen_expr)
                          (atom "."))
                       (self#formatNonSequencyExpression ~parent:x e))
                else Some (makeLetSequence (self#letList x))
              | Pexp_send (e, s) ->
                let needparens =
                  match e.pexp_desc with
                  | Pexp_apply (ee, _) ->
                    (match printedStringAndFixityExpr ee with
                    | UnaryPostfix "^" -> true
                    | _ -> false)
                  | _ -> false
                in
                let lhs = self#simple_enough_to_be_lhs_dot_send e in
                let lhs =
                  if needparens then makeList ~wrap:("(", ")") [ lhs ] else lhs
                in
                Some (label (makeList [ lhs; atom "#" ]) (atom s.txt))
              | Pexp_unreachable -> Some (atom ".")
              | _ -> None
            in
            match item with
            | None -> None
            | Some i -> Some (source_map ~loc:x.pexp_loc i)

        (* Renders jsx children. Returns None if it is not a valid JSX child
         * structure and must be rendered as spread.  You cannot render any list of
         * JSX children in Reason unless it is nil-terminated. Otherwise you must use
         * spread. *)
        method formatJsxChildrenNonSpread expr processedRev =
          let formatJsxChild x =
            match x with
            | { pexp_desc = Pexp_apply _; _ } as e ->
              (* Pipe first behaves differently according to the expression on the
               * right. In example (1) below, it's a `SpecificInfixPrecedence`; in
               * (2), however, it's `Simple` and doesn't need to be wrapped in parens.
               *
               * (1). <div> {items->Belt.Array.map(ReasonReact.string)->ReasonReact.array} </div>;
               * (2). <Foo> (title === "" ? [1, 2, 3] : blocks)->Foo.toString </Foo>; *)
              if
                Reason_heuristics.isPipeFirst e
                && not (Reason_heuristics.isPipeFirstWithNonSimpleJSXChild e)
              then self#formatPipeFirst e
              else
                self#inline_braces#simplifyUnparseExpr
                  ~inline:true
                  ~wrap:("{", "}")
                  e
            (* No braces - very simple *)
            | { pexp_desc = Pexp_ident li; _ } -> self#longident_loc li
            | { pexp_desc = Pexp_constant constant; _ } as x ->
              let raw_literal, _ =
                Reason_attributes.extract_raw_literal x.pexp_attributes
              in
              self#constant ?raw_literal constant
            | _ ->
              (* Currently spreading a list, or having a list as a child must be
               * wrapped in { }. You can remove the entire even_wrap_simple arg
               * when that is fixed (there is a conflict in grammar when allowing
               * a [] without {[]} as child. *)
              (* Simple child that has jsx: <hi> </hi> *)
              (* Simple child that doesn't have jsx: "hello" *)
              (* Simple child that doesn't have jsx but is a "::" and requires
                 braces: [a, b] *)
              self#inline_braces#simplifyUnparseExpr
                ~inline:true
                ~wrap:("{", "}")
                x
          in
          match expr with
          | { pexp_desc = Pexp_construct ({ txt = Lident "[]"; _ }, None); _ }
            ->
            (match processedRev with
            | [] -> None
            | _ :: _ -> Some (List.rev processedRev))
          | { pexp_desc =
                Pexp_construct
                  ( { txt = Lident "::"; _ }
                  , Some { pexp_desc = Pexp_tuple [ hd; tl ]; _ } )
            ; _
            } ->
            self#formatJsxChildrenNonSpread
              tl
              (formatJsxChild hd :: processedRev)
          | _ -> None

        method direction_flag =
          function Upto -> atom "to" | Downto -> atom "downto"

        method payload ppxToken ppxId e =
          let wrap = "[" ^ ppxToken ^ ppxId.txt, "]" in
          let wrap_prefix str (x, y) = x ^ str, y in
          let pad = true, false in
          let postSpace = true in
          match e with
          | PStr [] -> atom ("[" ^ ppxToken ^ ppxId.txt ^ "]")
          | PStr [ itm ] ->
            makeList ~break:Layout.IfNeed ~wrap ~pad [ self#structure_item itm ]
          | PStr (_ :: _ as items) ->
            let rows = List.map self#structure_item items in
            makeList
              ~wrap
              ~break:Layout.Always
              ~pad
              ~postSpace
              ~sep:(Layout.Sep ";")
              rows
          | PTyp x ->
            let wrap = wrap_prefix ":" wrap in
            makeList ~wrap ~break:Layout.IfNeed ~pad [ self#core_type x ]
          (* Signatures in attributes were added recently *)
          | PSig [] -> atom ("[" ^ ppxToken ^ ppxId.txt ^ ":]")
          | PSig [ x ] ->
            let wrap = wrap_prefix ":" wrap in
            makeList ~break:Layout.IfNeed ~wrap ~pad [ self#signature_item x ]
          | PSig items ->
            let wrap = wrap_prefix ":" wrap in
            let rows = List.map self#signature_item items in
            makeList
              ~wrap
              ~break:Layout.IfNeed
              ~pad
              ~postSpace
              ~sep:(Layout.Sep ";")
              rows
          | PPat (x, None) ->
            let wrap = wrap_prefix "?" wrap in
            makeList
              ~wrap
              ~break:Layout.IfNeed
              ~pad
              [ self#pattern_at_least_as_simple_as_alias_or_or x ]
          | PPat (x, Some e) ->
            let wrap = wrap_prefix "?" wrap in
            makeList
              ~wrap
              ~break:Layout.IfNeed
              ~pad
              ~postSpace
              [ self#pattern_at_least_as_simple_as_alias_or_or x
              ; label ~space:true (atom "when") (self#unparseExpr e)
              ]

        (* [% ...] *)
        method extension (s, p) =
          match s.txt with
          (* We special case "mel.obj" for now to allow for a nicer interop with
           * BuckleScript. We might be able to generalize to any kind of record
           * looking thing with struct keys. *)
          | "mel.obj" -> self#formatBsObjExtensionSugar p
          | _ -> self#payload "%" s p

        method item_extension (s, e) = self#payload "%%" s e

        (* [@ ...] Simple attributes *)
        method attribute =
          function
          | { attr_name = { Location.txt = "ocaml.doc" | "ocaml.text"; _ }
            ; attr_payload =
                PStr
                  [ { pstr_desc =
                        Pstr_eval
                          ( { pexp_desc =
                                Pexp_constant (Pconst_string (text, _, None))
                            ; _
                            }
                          , _ )
                    ; pstr_loc
                    }
                  ]
            ; _
            } ->
            let break = if text = "" then Layout.IfNeed else Always_rec in
            let text = if text = "" then "/**/" else "/**" ^ text ^ "*/" in
            makeList
              ~inline:(true, true)
              ~postSpace:true
              ~preSpace:true
              ~indent:0
              ~break
              [ atom ~loc:pstr_loc text ]
          | { attr_name; attr_payload; _ } ->
            self#payload "@" attr_name attr_payload

        (* [@@ ... ] Attributes that occur after a major item in a
           structure/class *)
        method item_attribute = self#attribute

        (* [@@ ...] Attributes that occur not *after* an item in some
           structure/class/sig, but rather as their own standalone item. Note
           that syntactic distinction between item_attribute and
           floating_attribute is no longer necessary with Reason. Thank you
           semicolons. *)
        method floating_attribute = self#item_attribute
        method attributes l = List.map self#attribute l

        method attach_std_attrs l toThis =
          let l = Reason_attributes.extractStdAttrs l in
          match l with
          | [] -> toThis
          | _ :: _ ->
            makeList
              ~postSpace:true
              (List.concat [ self#attributes l; [ toThis ] ])

        method attach_std_item_attrs ?(allowUncurry = true) ?extension l toThis
            =
          let attrs = Reason_attributes.partitionAttributes ~allowUncurry l in
          match extension, attrs.stdAttrs with
          | None, [] -> toThis
          | Some id, _ ->
            makeList
              ~wrap:("[%" ^ id.txt, "]")
              ~indent:1
              ~pad:(true, false)
              ~break:Layout.IfNeed
              (List.map self#item_attribute l @ [ toThis ])
          | None, _ ->
            makeList
              ~postSpace:true
              ~indent:0
              ~break:Always
              ~inline:(true, true)
              (List.map self#item_attribute l @ [ toThis ])

        method exception_declaration ed =
          let pcd_name = ed.pext_name in
          let pcd_loc = ed.pext_loc in
          let pcd_attributes = [] in
          let exn_arg =
            match ed.pext_kind with
            | Pext_decl (vars, args, type_opt) ->
              let pcd_args, pcd_res = args, type_opt in
              [ self#type_variant_leaf_nobar
                  { pcd_name
                  ; pcd_args
                  ; pcd_res
                  ; pcd_loc
                  ; pcd_attributes
                  ; pcd_vars = vars
                  }
              ]
            | Pext_rebind id ->
              [ atom pcd_name.txt; atom "="; self#longident_loc id ]
          in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes
              ~partDoc:true
              ed.pext_attributes
          in
          let layout =
            self#attach_std_item_attrs
              stdAttrs
              (label
                 ~space:true
                 (atom "exception")
                 (makeList ~postSpace:true ~inline:(true, true) exn_arg))
          in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:ed.pext_loc
            ~layout
            ()

        (* Note: that override doesn't appear in class_sig_field, but does occur
           in class/object expressions. TODO: TODOATTRIBUTES *)
        method method_sig_flags_for s =
          function
          | Virtual -> [ atom "virtual"; atom s ]
          | Concrete -> [ atom s ]

        method value_type_flags_for s =
          function
          | Virtual, Mutable -> [ atom "virtual"; atom "mutable"; atom s ]
          | Virtual, Immutable -> [ atom "virtual"; atom s ]
          | Concrete, Mutable -> [ atom "mutable"; atom s ]
          | Concrete, Immutable -> [ atom s ]

        method class_sig_field x =
          match x.pctf_desc with
          | Pctf_inherit ct ->
            label ~space:true (atom "inherit") (self#class_constructor_type ct)
          | Pctf_val (s, mf, vf, ct) ->
            let valueFlags = self#value_type_flags_for (s.txt ^ ":") (vf, mf) in
            label
              ~space:true
              (label
                 ~space:true
                 (atom "val")
                 (makeList
                    ~postSpace:true
                    ~inline:(false, true)
                    ~break:IfNeed
                    valueFlags))
              (self#core_type ct)
          | Pctf_method (s, pf, vf, ct) ->
            let methodFlags = self#method_sig_flags_for (s.txt ^ ":") vf in
            let pubOrPrivate =
              match pf with Private -> "pri" | Public -> "pub"
            in
            let m =
              label
                ~space:true
                (label
                   ~space:true
                   (atom pubOrPrivate)
                   (makeList
                      ~postSpace:true
                      ~inline:(false, true)
                      ~break:IfNeed
                      methodFlags))
                (self#core_type ct)
            in
            self#attach_std_item_attrs x.pctf_attributes m
          | Pctf_constraint (ct1, ct2) ->
            label
              ~space:true
              (atom "constraint")
              (label
                 ~space:true
                 (makeList ~postSpace:true [ self#core_type ct1; atom "=" ])
                 (self#core_type ct2))
          | Pctf_attribute a -> self#floating_attribute a
          | Pctf_extension e -> self#item_extension e

        (*
           * /** doc comment */                                    (* formattedDocs *)
         * [@bs.val] [@bs.module "react-dom"]                    (* formattedAttrs *)
         * external render : reactElement => element => unit =   (* frstHalf *)
         *   "render";                                           (* sndHalf *)

         * To improve the formatting with breaking & indentation:
         *   * consider the part before the '=' as a label
         *   * combine that label with '=' in a list
         *   * consider the part after the '=' as a list
         *   * combine both parts as a label
         *   * format the doc comment with a ~postSpace:true (inline, not inline) list
         *   * format the attributes with a ~postSpace:true (inline, inline) list
         *   * format everything together in a ~postSpace:true (inline, inline) list
         *     for nicer breaking
        *)
        method primitive_declaration ?extension vd =
          let external_label = add_extension_sugar "external" extension in
          let lblBefore =
            label
              ~space:true
              (makeList
                 [ makeList
                     ~postSpace:true
                     [ atom external_label; protectIdentifier vd.pval_name.txt ]
                 ; atom ":"
                 ])
              (self#core_type vd.pval_type)
          in
          let primDecl =
            match vd.pval_prim with
            | [ "" ] -> lblBefore
            | _ ->
              let frstHalf = makeList ~postSpace:true [ lblBefore; atom "=" ] in
              let sndHalf =
                makeSpacedBreakableInlineList
                  (List.map self#constant_string_for_primitive vd.pval_prim)
              in
              label ~space:true frstHalf sndHalf
          in
          match vd.pval_attributes with
          | [] -> primDecl
          | attrs ->
            let { Reason_attributes.stdAttrs; docAttrs; _ } =
              Reason_attributes.partitionAttributes ~partDoc:true attrs
            in
            let docs = List.map self#item_attribute docAttrs in
            let formattedDocs = makeList ~postSpace:true docs in
            let attrs = List.map self#item_attribute stdAttrs in
            let formattedAttrs = makeSpacedBreakableInlineList attrs in
            let layouts =
              match docAttrs, stdAttrs with
              | [], _ -> [ formattedAttrs; primDecl ]
              | _, [] -> [ formattedDocs; primDecl ]
              | _ -> [ formattedDocs; formattedAttrs; primDecl ]
            in
            makeSpacedBreakableInlineList layouts

        method classTypeSigsAndRest x =
          match x.pcty_desc with
          | Pcty_signature cs ->
            let { pcsig_self = ct; pcsig_fields = l } = cs in
            let instTypeFields = List.map self#class_sig_field l in
            let allItems =
              match ct.ptyp_desc with
              | Ptyp_any -> instTypeFields
              | _ ->
                label ~space:true (atom "as") (self#core_type ct)
                :: instTypeFields
            in
            allItems
          | _ -> [ self#class_instance_type x ]

        method class_instance_type x =
          match x.pcty_desc with
          | Pcty_signature _ | Pcty_open _ ->
            let opens, rest = self#classTypeOpens x in
            let cs = self#classTypeSigsAndRest rest in
            self#attach_std_item_attrs
              ~allowUncurry:false
              x.pcty_attributes
              (makeList
                 ~wrap:("{", "}")
                 ~postSpace:true
                 ~break:Layout.Always_rec
                 (List.map semiTerminated (List.concat [ opens; cs ])))
          | Pcty_constr (li, l) ->
            self#attach_std_attrs
              x.pcty_attributes
              (match l with
              | [] -> self#longident_loc li
              | _ :: _ ->
                label
                  (self#longident_loc li)
                  (makeList
                     ~wrap:("(", ")")
                     ~sep:commaTrail
                     (List.map self#core_type l)))
          | Pcty_extension e ->
            self#attach_std_item_attrs x.pcty_attributes (self#extension e)
          | Pcty_arrow _ ->
            failwith "class_instance_type should not be printed with Pcty_arrow"

        method classTypeOpens x =
          let rec gatherOpens acc opn =
            match opn.pcty_desc with
            | Pcty_open (md, ct) ->
              let li = md.popen_expr in
              gatherOpens
                (source_map
                   ~loc:li.loc
                   (label
                      ~space:true
                      (atom ("open" ^ override md.popen_override))
                      (self#longident_loc li))
                :: acc)
                ct
            | _ -> List.rev acc, opn
          in
          gatherOpens [] x

        method class_declaration_list l =
          let class_declaration
                ?(class_keyword = false)
                ({ pci_params = ls
                 ; pci_name = { txt; _ }
                 ; pci_virt
                 ; pci_loc
                 ; _
                 } as x)
            =
            let firstToken, pattern, patternAux =
              self#class_opening class_keyword txt pci_virt ls
            in
            let classBinding =
              self#wrappedClassBinding firstToken pattern patternAux x.pci_expr
            in
            source_map
              ~loc:pci_loc
              (self#attach_std_item_attrs x.pci_attributes classBinding)
          in
          match l with
          | [] ->
            raise (NotPossible "Class definitions will have at least one item.")
          | x :: rest ->
            makeNonIndentedBreakingList
              (class_declaration ~class_keyword:true x
              :: List.map class_declaration rest)

        (* For use with [class type a = class_instance_type]. Class type
           declarations/definitions declare the types of instances generated by
           class constructors. We have to call self#class_instance_type because
           self#class_constructor_type would add a "new" before the type. TODO:
           TODOATTRIBUTES: *)
        method class_type_declaration_list l =
          let class_type_declaration
                kwd
                ({ pci_params = ls; pci_name; pci_attributes; _ } as x)
            =
            let opener =
              match x.pci_virt with
              | Virtual -> kwd ^ " " ^ "virtual"
              | Concrete -> kwd
            in

            let upToName =
              if ls == []
              then label ~space:true (atom opener) (atom pci_name.txt)
              else
                label
                  ~space:true
                  (label ~space:true (atom opener) (atom pci_name.txt))
                  (self#class_params_def ls)
            in
            let includingEqual =
              makeList ~postSpace:true [ upToName; atom "=" ]
            in
            let { Reason_attributes.stdAttrs; docAttrs; _ } =
              Reason_attributes.partitionAttributes ~partDoc:true pci_attributes
            in
            let layout =
              self#attach_std_item_attrs stdAttrs
              @@ label
                   ~space:true
                   includingEqual
                   (self#class_instance_type x.pci_expr)
            in
            self#attachDocAttrsToLayout
              ~stdAttrs
              ~docAttrs
              ~loc:pci_name.loc
              ~layout
              ()
          in
          match l with
          | [] ->
            failwith "Should not call class_type_declaration with no classes"
          | [ x ] -> class_type_declaration "class type" x
          | x :: xs ->
            makeList
              ~break:Always_rec
              ~indent:0
              ~inline:(true, true)
              (class_type_declaration "class type" x
              :: List.map (class_type_declaration "and") xs)

        (* Formerly the [class_type] Notice how class_constructor_type doesn't
           have any type attributes - class_instance_type does. TODO: Divide
           into class_constructor_types that allow arrows and ones that
           don't. *)
        method class_constructor_type x =
          match x.pcty_desc with
          | Pcty_arrow _ ->
            let rec allArrowSegments acc = function
              | { pcty_desc = Pcty_arrow (l, ct1, ct2); _ } ->
                allArrowSegments
                  (self#type_with_label (l, ct1, false) :: acc)
                  ct2
              (* This "new" is unfortunate. See reason_parser.mly for
                 details. *)
              | xx -> List.rev acc, self#class_constructor_type xx
            in
            let params, return = allArrowSegments [] x in
            let normalized =
              makeList
                ~break:IfNeed
                ~sep:(Sep "=>")
                ~preSpace:true
                ~postSpace:true
                ~inline:(true, true)
                [ makeCommaBreakableListSurround "(" ")" params; return ]
            in
            source_map ~loc:x.pcty_loc normalized
          | _ ->
            (* Unfortunately, we have to have final components of a
               class_constructor_type be prefixed with the `new` keyword.
               Hopefully this is temporary. *)
            self#class_instance_type x

        method non_arrowed_class_constructor_type x =
          match x.pcty_desc with
          | Pcty_arrow _ ->
            source_map
              ~loc:x.pcty_loc
              (formatPrecedence (self#class_constructor_type x))
          | _ -> self#class_instance_type x

        method class_field x =
          let itm =
            match x.pcf_desc with
            | Pcf_inherit (ovf, ce, so) ->
              let inheritText = "inherit" ^ override ovf in
              let inheritExp = self#class_expr ce in
              label
                ~space:true
                (atom inheritText)
                (match so with
                | None -> inheritExp
                | Some s -> label ~space:true inheritExp (atom ("as " ^ s.txt)))
            | Pcf_val (s, mf, Cfk_concrete (ovf, e)) ->
              let opening =
                match mf with
                | Mutable ->
                  let mutableName = [ atom "mutable"; atom s.txt ] in
                  label
                    ~space:true
                    (atom ("val" ^ override ovf))
                    (makeList
                       ~postSpace:true
                       ~inline:(false, true)
                       ~break:IfNeed
                       mutableName)
                | Immutable ->
                  label ~space:true (atom ("val" ^ override ovf)) (atom s.txt)
              in
              let valExprAndConstraint =
                match e.pexp_desc with
                | Pexp_constraint (ex, ct) ->
                  let openingWithTypeConstraint =
                    formatTypeConstraint opening (self#core_type ct)
                  in
                  label
                    ~space:true
                    (makeList
                       ~postSpace:true
                       [ openingWithTypeConstraint; atom "=" ])
                    (self#unparseExpr ex)
                | _ ->
                  label
                    ~space:true
                    (makeList ~postSpace:true [ opening; atom "=" ])
                    (self#unparseExpr e)
              in
              valExprAndConstraint
            | Pcf_val (s, mf, Cfk_virtual ct) ->
              let opening =
                match mf with
                | Mutable ->
                  let mutableVirtualName =
                    [ atom "mutable"; atom "virtual"; atom s.txt ]
                  in
                  let openingTokens =
                    makeList
                      ~postSpace:true
                      ~inline:(false, true)
                      ~break:IfNeed
                      mutableVirtualName
                  in
                  label ~space:true (atom "val") openingTokens
                | Immutable ->
                  let virtualName = [ atom "virtual"; atom s.txt ] in
                  let openingTokens =
                    makeList
                      ~postSpace:true
                      ~inline:(false, true)
                      ~break:IfNeed
                      virtualName
                  in
                  label ~space:true (atom "val") openingTokens
              in
              formatTypeConstraint opening (self#core_type ct)
            | Pcf_method (s, pf, Cfk_virtual ct) ->
              let opening =
                match pf with
                | Private ->
                  let privateVirtualName = [ atom "virtual"; atom s.txt ] in
                  let openingTokens =
                    makeList
                      ~postSpace:true
                      ~inline:(false, true)
                      ~break:IfNeed
                      privateVirtualName
                  in
                  label ~space:true (atom "pri") openingTokens
                | Public ->
                  let virtualName = [ atom "virtual"; atom s.txt ] in
                  let openingTokens =
                    makeList
                      ~postSpace:true
                      ~inline:(false, true)
                      ~break:IfNeed
                      virtualName
                  in
                  label ~space:true (atom "pub") openingTokens
              in
              formatTypeConstraint opening (self#core_type ct)
            | Pcf_method (s, pf, Cfk_concrete (ovf, e)) ->
              let methodText =
                let postFix = if ovf == Override then "!" else "" in
                match pf with
                | Private -> "pri" ^ postFix
                | Public -> "pub" ^ postFix
              in
              (* Should refactor the binding logic so faking out the AST isn't
                 needed, currently, it includes a ton of nuanced logic around
                 recovering explicitly polymorphic type definitions, and that
                 furthermore, that representation... Actually, let's do it.

                 For some reason, concrete methods are only ever parsed as
                 Pexp_poly. If there *is* no polymorphic function for the
                 method, then the return value of the function is wrapped in a
                 ghost Pexp_poly with [None] for the type vars.*)
              (match e.pexp_desc with
              | Pexp_poly
                  ( { pexp_desc =
                        Pexp_constraint
                          (methodFunWithNewtypes, nonVarifiedExprType)
                    ; _
                    }
                  , Some
                      { ptyp_desc = Ptyp_poly (typeVars, varifiedPolyType); _ }
                  )
                when let leadingAbstractVars, _ =
                       self#leadingCurriedAbstractTypes methodFunWithNewtypes
                     in
                     self#isRenderableAsPolymorphicAbstractTypes
                       typeVars
                       (* If even artificially varified. Don't know until this
                          returns*)
                       varifiedPolyType
                       leadingAbstractVars
                       nonVarifiedExprType ->
                let leadingAbstractVars, _ =
                  self#leadingCurriedAbstractTypes methodFunWithNewtypes
                in
                self#locallyAbstractPolymorphicFunctionBinding
                  methodText
                  (atom s.txt)
                  methodFunWithNewtypes
                  leadingAbstractVars
                  nonVarifiedExprType
              | Pexp_poly (e, Some ct) ->
                self#formatSimplePatternBinding
                  methodText
                  (atom s.txt)
                  (Some (source_map ~loc:ct.ptyp_loc (self#core_type ct)))
                  (self#unparseExprApplicationItems e)
              (* This form means that there is no type constraint - it's a
                 strange node name.*)
              | Pexp_poly (e, None) ->
                self#wrappedBinding methodText ~arrow:"=>" (atom s.txt) [] e
              | _ ->
                failwith "Concrete methods should only ever have Pexp_poly.")
            | Pcf_constraint (ct1, ct2) ->
              label
                ~space:true
                (atom "constraint")
                (makeList
                   ~postSpace:true
                   ~inline:(true, false)
                   [ makeList ~postSpace:true [ self#core_type ct1; atom "=" ]
                   ; self#core_type ct2
                   ])
            | Pcf_initializer e ->
              label
                ~space:true
                (atom "initializer")
                (self#simplifyUnparseExpr e)
            | Pcf_attribute a -> self#floating_attribute a
            | Pcf_extension e ->
              (* And don't forget, we still need to print post_item_attributes
                 even for this case *)
              self#item_extension e
          in
          let layout = self#attach_std_attrs x.pcf_attributes itm in
          source_map ~loc:x.pcf_loc layout

        method class_self_pattern_and_structure
          { pcstr_self = p; pcstr_fields = l } =
          let fields = List.map self#class_field l in
          (* Recall that by default self is bound to "this" at parse time. You'd
             have to go out of your way to bind it to "_". *)
          match p.ppat_attributes, p.ppat_desc with
          | [], Ppat_var { txt = "this"; _ } -> fields
          | _ ->
            let field = label ~space:true (atom "as") (self#pattern p) in
            source_map ~loc:p.ppat_loc field :: fields

        method simple_class_expr x =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.pcl_attributes
          in
          if stdAttrs != []
          then
            formatSimpleAttributed
              (self#simple_class_expr { x with pcl_attributes = [] })
              (self#attributes stdAttrs)
          else
            let itm =
              match x.pcl_desc with
              | Pcl_constraint (ce, ct) ->
                formatTypeConstraint
                  (self#class_expr ce)
                  (self#class_constructor_type ct)
              (* In OCaml,
               * - In the most recent version of OCaml, when in the top level of a
               *   module, let _ = ... is a PStr_eval.
               * - When in a function, it is a Pexp_let PPat_any
               * - When in class pre-member let bindings it is a Pcl_let PPat_any
               *
               *  Reason normalizes all of these to be simple imperative expressions
               *  with trailing semicolons, *except* in the case of classes because it
               *  will likely introduce a conflict with some proposed syntaxes for
               *  objects.
              *)
              | Pcl_let _ | Pcl_structure _ | Pcl_open _ ->
                let opens, rest = self#classExprOpens x in
                let rows = self#classExprLetsAndRest rest in
                makeList
                  ~wrap:("{", "}")
                  ~inline:(true, false)
                  ~postSpace:true
                  ~break:Always_rec
                  (List.map semiTerminated (List.concat [ opens; rows ]))
              | Pcl_extension e -> self#extension e
              | _ -> formatPrecedence (self#class_expr x)
            in
            source_map ~loc:x.pcl_loc itm

        method classExprLetsAndRest x =
          match x.pcl_desc with
          | Pcl_structure cs -> self#class_self_pattern_and_structure cs
          | Pcl_let (rf, l, ce) ->
            (* For "letList" bindings, the start/end isn't as simple as with
             * module value bindings. For "let lists", the sequences were formed
             * within braces {}. The parser relocates the first let binding to the
             * first brace. *)
            let binding =
              source_map
                ~loc:(self#bindingsLocationRange l)
                (self#bindings (rf, l))
            in
            binding :: self#classExprLetsAndRest ce
          | Pcl_open (_, ce) -> self#classExprLetsAndRest ce
          | _ -> [ self#class_expr x ]

        method classExprOpens x =
          let rec gatherOpens acc opn =
            match opn.pcl_desc with
            | Pcl_open (md, ce) ->
              let li = md.popen_expr in
              gatherOpens
                (source_map
                   ~loc:li.loc
                   (label
                      ~space:true
                      (atom ("open" ^ override md.popen_override))
                      (self#longident_loc li))
                :: acc)
                ce
            | _ -> List.rev acc, opn
          in
          gatherOpens [] x

        method class_expr x =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes x.pcl_attributes
          in
          (* We cannot handle the attributes here. Must handle them in each
             item *)
          if stdAttrs != []
          then
            (* Do not need a "simple" attributes precedence wrapper. *)
            formatAttributed
              (self#simple_class_expr { x with pcl_attributes = [] })
              (self#attributes stdAttrs)
          else
            match x.pcl_desc with
            | Pcl_fun _ ->
              (match self#curriedConstructorPatternsAndReturnVal x with
              | None, _ ->
                (* x just matched Pcl_fun, there is at least one parameter *)
                assert false
              | Some args, e ->
                label
                  ~space:true
                  (makeList
                     ~postSpace:true
                     [ label ~space:true (atom funToken) args; atom "=>" ])
                  (self#class_expr e))
            | Pcl_apply _ ->
              formatAttachmentApplication
                applicationFinalWrapping
                None
                (self#classExpressionToFormattedApplicationItems x, None)
            | Pcl_constr (li, []) ->
              label ~space:true (atom "class") (self#longident_loc li)
            | Pcl_constr (li, l) ->
              label
                (makeList
                   ~postSpace:true
                   [ atom "class"; self#longident_loc li ])
                (makeTup (List.map self#non_arrowed_non_simple_core_type l))
            | Pcl_open _ | Pcl_constraint _ | Pcl_extension _ | Pcl_let _
            | Pcl_structure _ ->
              self#simple_class_expr x

        method classStructure ?(forceBreak = false) ?(wrap = "", "") cs =
          let left, right = wrap in
          makeList
            ~sep:(Layout.Sep ";")
            ~wrap:(left ^ "{", "}" ^ right)
            ~break:(if forceBreak then Layout.Always else Layout.IfNeed)
            ~postSpace:true
            ~inline:(true, false)
            (self#class_self_pattern_and_structure cs)

        method signature signatureItems =
          match signatureItems with
          | [] -> atom ""
          | first :: _ as signatureItems ->
            let last =
              match List.rev signatureItems with
              | last :: _ -> last
              | [] -> assert false
            in
            let loc_start = first.psig_loc.loc_start in
            let loc_end = last.psig_loc.loc_end in
            let items =
              groupAndPrint
                ~xf:self#signature_item
                ~getLoc:(fun x -> x.psig_loc)
                ~comments:self#comments
                signatureItems
            in
            source_map
              ~loc:{ loc_start; loc_end; loc_ghost = false }
              (makeList
                 ~postSpace:true
                 ~break:Layout.Always_rec
                 ~indent:0
                 ~inline:(true, false)
                 ~sep:(SepFinal (";", ";"))
                 items)

        method signature_item item : Layout.t =
          match item.psig_desc with
          | Psig_extension ((extension, PSig [ item ]), _attrs) ->
            (match item.psig_desc with
            (* In case of a value or `external`, the extension gets inlined
               `let%private a = 1` *)
            | Psig_value ({ pval_prim = [ _ ]; _ } as vd) ->
              self#primitive_declaration ~extension vd
            | Psig_value vd -> self#val_binding ~extension vd
            | Psig_module pmd -> self#psig_module ~extension pmd
            | Psig_recmodule pmd -> self#psig_recmodule ~extension pmd
            | Psig_open od -> self#psig_open ~extension od
            | Psig_type (rf, l) -> self#type_def_list ~extension rf l
            | Psig_typext te -> self#type_extension ~extension te
            | _ -> self#payload "%%" extension (PSig [ item ]))
          | _ -> self#signature_item' item

        method val_binding ?extension vd =
          let intro = add_extension_sugar "let" extension in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes
              ~partDoc:true
              vd.pval_attributes
          in
          let layout =
            self#attach_std_item_attrs
              stdAttrs
              (formatTypeConstraint
                 (label
                    ~space:true
                    (atom intro)
                    (source_map
                       ~loc:vd.pval_name.loc
                       (protectIdentifier vd.pval_name.txt)))
                 (self#core_type vd.pval_type))
          in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:vd.pval_loc
            ~layout
            ()

        method psig_module ?extension pmd =
          let layout =
            let prefix = add_extension_sugar "module" extension in
            match pmd.pmd_type.pmty_desc with
            | Pmty_alias alias ->
              label
                ~space:true
                (makeList
                   ~postSpace:true
                   [ atom prefix; atom (moduleIdent pmd.pmd_name); atom "=" ])
                (self#longident_loc alias)
            | _ ->
              let letPattern =
                makeList
                  [ makeList
                      ~postSpace:true
                      [ atom prefix; atom (moduleIdent pmd.pmd_name) ]
                  ; atom ":"
                  ]
              in
              self#module_type letPattern pmd.pmd_type
          in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes
              ~partDoc:true
              pmd.pmd_attributes
          in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:pmd.pmd_name.loc
            ~layout:(self#attach_std_item_attrs stdAttrs @@ layout)
            ()

        method psig_recmodule ?extension decls =
          let items =
            List.mapi
              (fun i xx ->
                 let { Reason_attributes.stdAttrs; docAttrs; _ } =
                   Reason_attributes.partitionAttributes
                     ~partDoc:true
                     xx.pmd_attributes
                 in
                 let letPattern =
                   makeList
                     [ makeList
                         ~postSpace:true
                         [ atom
                             (if i == 0
                              then
                                add_extension_sugar "module" extension ^ " rec"
                              else "and")
                         ; atom (moduleIdent xx.pmd_name)
                         ]
                     ; atom ":"
                     ]
                 in
                 let layout =
                   self#attach_std_item_attrs
                     stdAttrs
                     (self#module_type ~space:true letPattern xx.pmd_type)
                 in
                 let layoutWithDocAttrs =
                   self#attachDocAttrsToLayout
                     ~stdAttrs
                     ~docAttrs
                     ~loc:xx.pmd_name.loc
                     ~layout
                     ()
                 in
                 extractLocModDecl xx, layoutWithDocAttrs)
              decls
          in
          makeNonIndentedBreakingList
            (groupAndPrint
               ~xf:(fun (_, layout) -> layout)
               ~getLoc:(fun (loc, _) -> loc)
               ~comments:self#comments
               items)

        method psig_open ?extension od =
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes
              ~partDoc:true
              od.popen_attributes
          in
          let layout =
            let open_prefix =
              add_open_extension_sugar ~override:od.popen_override extension
            in
            self#attach_std_item_attrs stdAttrs
            @@ label
                 ~space:true
                 (atom open_prefix)
                 (self#longident_loc od.popen_expr)
          in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:od.popen_expr.loc
            ~layout
            ()

        method modtype x ~delim =
          let name = atom x.pmtd_name.txt in
          let letPattern =
            makeList ~postSpace:true [ atom "module type"; name; atom delim ]
          in
          let main =
            match x.pmtd_type with
            | None -> makeList ~postSpace:true [ atom "module type"; name ]
            | Some mt -> self#module_type letPattern mt
          in
          let { Reason_attributes.stdAttrs; docAttrs; _ } =
            Reason_attributes.partitionAttributes
              ~partDoc:true
              x.pmtd_attributes
          in
          let layout = self#attach_std_item_attrs stdAttrs main in
          self#attachDocAttrsToLayout
            ~stdAttrs
            ~docAttrs
            ~loc:x.pmtd_name.loc
            ~layout
            ()

        method signature_item' x : Layout.t =
          let item : Layout.t =
            match x.psig_desc with
            | Psig_type (rf, l) -> self#type_def_list rf l
            | Psig_value vd ->
              if vd.pval_prim != []
              then self#primitive_declaration vd
              else self#val_binding vd
            | Psig_typext te -> self#type_extension te
            | Psig_exception ed ->
              self#exception_declaration
                { ed.ptyexn_constructor with
                  pext_attributes =
                    ed.ptyexn_attributes @ ed.ptyexn_constructor.pext_attributes
                }
            | Psig_class l ->
              let class_description
                    ?(class_keyword = false)
                    ({ pci_params = ls; pci_name = { txt; _ }; pci_loc; _ } as x)
                =
                let firstToken, pattern, patternAux =
                  self#class_opening class_keyword txt x.pci_virt ls
                in
                let withColon =
                  self#wrapCurriedFunctionBinding
                    ~arrow:":"
                    ~spaceBeforeArrow:false
                    firstToken
                    pattern
                    patternAux
                    ([ self#class_constructor_type x.pci_expr ], None)
                in
                let { Reason_attributes.stdAttrs; docAttrs; _ } =
                  Reason_attributes.partitionAttributes
                    ~partDoc:true
                    x.pci_attributes
                in
                let layout = self#attach_std_item_attrs stdAttrs withColon in
                source_map
                  ~loc:pci_loc
                  (self#attachDocAttrsToLayout
                     ~stdAttrs
                     ~docAttrs
                     ~loc:x.pci_name.loc
                     ~layout
                     ())
              in
              makeNonIndentedBreakingList
                (match l with
                | [] -> raise (NotPossible "No recursive class bindings")
                | [ x ] -> [ class_description ~class_keyword:true x ]
                | x :: xs ->
                  class_description ~class_keyword:true x
                  :: List.map class_description xs)
            | Psig_module pmd -> self#psig_module pmd
            | Psig_open od -> self#psig_open od
            | Psig_include incl ->
              let { Reason_attributes.stdAttrs; docAttrs; _ } =
                Reason_attributes.partitionAttributes
                  ~partDoc:true
                  incl.pincl_attributes
              in
              let layout =
                self#attach_std_item_attrs stdAttrs
                @@ self#module_type (atom "include") incl.pincl_mod
              in
              self#attachDocAttrsToLayout
                ~stdAttrs
                ~docAttrs
                ~loc:incl.pincl_mod.pmty_loc
                ~layout
                ()
            | Psig_modtype x -> self#modtype x ~delim:"="
            | Psig_class_type l -> self#class_type_declaration_list l
            | Psig_recmodule decls -> self#psig_recmodule decls
            | Psig_attribute a -> self#floating_attribute a
            | Psig_extension ((({ loc; _ }, _) as ext), attrs) ->
              let { Reason_attributes.stdAttrs; docAttrs; _ } =
                Reason_attributes.partitionAttributes ~partDoc:true attrs
              in
              let layout =
                self#attach_std_item_attrs stdAttrs (self#item_extension ext)
              in
              self#attachDocAttrsToLayout ~stdAttrs ~docAttrs ~loc ~layout ()
            | Psig_modsubst { pms_name; pms_manifest; pms_attributes; pms_loc }
              ->
              let name = atom pms_name.txt in
              let main =
                makeList
                  ~postSpace:true
                  [ atom "module"
                  ; name
                  ; atom ":="
                  ; self#longident_loc pms_manifest
                  ]
              in
              let { Reason_attributes.stdAttrs; docAttrs; _ } =
                Reason_attributes.partitionAttributes
                  ~partDoc:true
                  pms_attributes
              in
              let layout = self#attach_std_item_attrs stdAttrs main in
              self#attachDocAttrsToLayout
                ~stdAttrs
                ~docAttrs
                ~loc:pms_loc
                ~layout
                ()
            | Psig_typesubst l -> self#type_def_list ~eq_symbol:":=" Recursive l
            | Psig_modtypesubst x -> self#modtype x ~delim:":="
          in
          source_map ~loc:x.psig_loc item

        method non_arrowed_module_type ?(space = true) letPattern x =
          match x.pmty_desc with
          | Pmty_alias li ->
            label
              ~space
              letPattern
              (formatPrecedence
                 (label ~space:true (atom "module") (self#longident_loc li)))
          | Pmty_typeof me ->
            let labelWithoutFinalWrap =
              label
                ~space:true
                (label
                   ~space:true
                   letPattern
                   (makeList
                      ~inline:(false, false)
                      ~wrap:("(", "")
                      ~postSpace:true
                      [ atom "module type of" ]))
                (self#module_expr me)
            in
            makeList ~wrap:("", ")") [ labelWithoutFinalWrap ]
          | _ -> self#simple_module_type ~space letPattern x

        method simple_module_type ?(space = true) letPattern x =
          match x.pmty_desc with
          | Pmty_ident li -> label ~space letPattern (self#longident_loc li)
          | Pmty_signature s ->
            let items =
              groupAndPrint
                ~xf:self#signature_item
                ~getLoc:(fun x -> x.psig_loc)
                ~comments:self#comments
                s
            in
            let shouldBreakLabel = match s with [] -> `Auto | _ -> `Always in
            label
              ~indent:0
              ~break:shouldBreakLabel
              (makeList
                 [ label
                     ~break:shouldBreakLabel
                     (makeList ~postSpace:true [ letPattern; atom "{" ])
                     (source_map
                        ~loc:x.pmty_loc
                        (makeList
                           ~break:(match s with [] -> IfNeed | _ -> Always)
                           ~inline:(true, true)
                           ~postSpace:true
                           ~sep:(SepFinal (";", ";"))
                           items))
                 ])
              (atom "}")
          | Pmty_extension (s, e) ->
            label ~space letPattern (self#payload "%" s e)
          | _ ->
            makeList
              ~break:IfNeed
              ~wrap:("", ")")
              [ self#module_type
                  ~space:false
                  (makeList ~pad:(false, true) ~wrap:("", "(") [ letPattern ])
                  x
              ]

        method module_type ?(space = true) letPattern x =
          let pmty =
            match x.pmty_desc with
            | Pmty_functor _ ->
              (* The segments that should be separated by arrows. *)
              let rec extract_args args xx =
                match xx.pmty_desc with
                | Pmty_functor (Unit, mt2) -> extract_args (`Unit :: args) mt2
                | Pmty_functor (Named ({ txt = s; _ }, mt1), mt2) ->
                  let arg =
                    match s with
                    | None -> self#module_type ~space:false (atom "") mt1
                    | Some s ->
                      self#module_type
                        ~space
                        (makeList [ atom s; atom ":" ])
                        mt1
                  in
                  extract_args (`Arg arg :: args) mt2
                | _ ->
                  let prepare_arg = function
                    | `Unit -> atom "()"
                    | `Arg x -> x
                  in
                  let args =
                    match args with
                    | [ `Unit ] -> []
                    | _ -> List.rev_map prepare_arg args
                  in
                  args, self#module_type (atom "") xx
              in
              let args, ret = extract_args [] x in
              label
                ~space
                letPattern
                (makeList
                   ~break:IfNeed
                   ~sep:(Sep "=>")
                   ~preSpace:true
                   ~inline:(true, true)
                   [ makeTup args; ret ])
            (* See comments in sugar_parser.mly about why WITH constraints aren't "non
             * arrowed" *)
            | Pmty_with (mt, l) ->
              let modSub atm li2 token =
                makeList
                  ~postSpace:true
                  [ atom "module"; atm; atom token; self#longident_loc li2 ]
              in
              let modtypeSub atm li modtype =
                label
                  (makeList
                     ~break:IfNeed
                     ~sep:(Sep " ")
                     [ atom "module type"; self#longident li; atm ])
                  (self#module_type (atom "") modtype)
              in
              let typeAtom = atom "type" in
              let eqAtom = atom "=" in
              let destrAtom = atom ":=" in
              let with_constraint = function
                | Pwith_type (li, td) ->
                  self#formatOneTypeDef
                    typeAtom
                    (makeList ~preSpace:true [ self#longident_loc li ])
                    eqAtom
                    td
                | Pwith_module (li, li2) ->
                  modSub (self#longident_loc li) li2 "="
                | Pwith_typesubst (_, td) ->
                  self#formatOneTypeDef
                    typeAtom
                    (atom ~loc:td.ptype_name.loc td.ptype_name.txt)
                    destrAtom
                    td
                | Pwith_modsubst (s, li2) ->
                  modSub (self#longident s.txt) li2 ":="
                | Pwith_modtype (s, modtype) -> modtypeSub eqAtom s.txt modtype
                | Pwith_modtypesubst (s, modtype) ->
                  modtypeSub destrAtom s.txt modtype
              in
              (match l with
              | [] -> self#module_type ~space letPattern mt
              | _ ->
                label
                  ~space
                  letPattern
                  (label
                     ~space:true
                     (makeList
                        ~preSpace:true
                        [ self#module_type ~space:false (atom "") mt
                        ; atom "with"
                        ])
                     (makeList
                        ~break:IfNeed
                        ~inline:(true, true)
                        ~sep:(Sep "and")
                        ~postSpace:true
                        ~preSpace:true
                        (List.map with_constraint l))))
            (* Seems like an infinite loop just waiting to happen. *)
            | _ -> self#non_arrowed_module_type ~space letPattern x
          in
          source_map ~loc:x.pmty_loc pmty

        method simple_module_expr ?(hug = false) x =
          match x.pmod_desc with
          | Pmod_unpack e ->
            let exprLayout =
              match e.pexp_desc with
              | Pexp_constraint (e, { ptyp_desc = Ptyp_package (lid, cstrs); _ })
                ->
                formatTypeConstraint
                  (makeList ~postSpace:true [ atom "val"; self#unparseExpr e ])
                  (self#typ_package ~mod_prefix:false lid cstrs)
              | _ -> makeList ~postSpace:true [ atom "val"; self#unparseExpr e ]
            in
            formatPrecedence exprLayout
          | Pmod_ident li ->
            ensureSingleTokenSticksToLabel (self#longident_loc li)
          | Pmod_constraint (unconstrainedRet, mt) ->
            let letPattern =
              makeList [ self#module_expr unconstrainedRet; atom ":" ]
            in
            formatPrecedence (self#module_type letPattern mt)
          | Pmod_structure s ->
            let wrap =
              if hug then if s = [] then "(", ")" else "({", "})" else "{", "}"
            in
            self#structure ~indent:None ~wrap s
          | _ ->
            (* For example, functor application will be wrapped. *)
            formatPrecedence ~wrap:("", "") (self#module_expr x)

        method module_expr x =
          match x.pmod_desc with
          | Pmod_functor _ ->
            let argsList, return =
              self#curriedFunctorPatternsAndReturnStruct x
            in
            (* See #19/20 in syntax.mls - cannot annotate return type at the
               moment. *)
            self#wrapCurriedFunctionBinding
              funToken
              ~sweet:true
              ~arrow:"=>"
              (makeTup argsList)
              []
              ([ self#moduleExpressionToFormattedApplicationItems return ], None)
          | Pmod_apply _ -> self#moduleExpressionToFormattedApplicationItems x
          | Pmod_extension (s, e) -> self#payload "%" s e
          | Pmod_unpack _ | Pmod_ident _ | Pmod_constraint _ | Pmod_structure _
            ->
            self#simple_module_expr x

        method recmodule ?extension decls =
          let items =
            List.mapi
              (fun i xx ->
                 let { Reason_attributes.stdAttrs; docAttrs; _ } =
                   Reason_attributes.partitionAttributes
                     ~partDoc:true
                     xx.pmb_attributes
                 in
                 let layout =
                   self#attach_std_item_attrs stdAttrs
                   @@ self#let_module_binding
                        (if i == 0
                         then add_extension_sugar "module" extension ^ " rec"
                         else "and")
                        (atom (moduleIdent xx.pmb_name))
                        xx.pmb_expr
                 in
                 let layoutWithDocAttrs =
                   self#attachDocAttrsToLayout
                     ~stdAttrs
                     ~docAttrs
                     ~loc:xx.pmb_name.loc
                     ~layout
                     ()
                 in
                 extractLocModuleBinding xx, layoutWithDocAttrs)
              decls
          in
          makeNonIndentedBreakingList
            (groupAndPrint
               ~xf:(fun (_, layout) -> layout)
               ~getLoc:(fun (loc, _) -> loc)
               ~comments:self#comments
               items)

        method pstr_open ?extension od =
          let open_prefix =
            add_open_extension_sugar ~override:od.popen_override extension
          in
          self#attach_std_item_attrs od.popen_attributes
          @@ label
               ~space:true
               (atom open_prefix)
               (self#moduleExpressionToFormattedApplicationItems od.popen_expr)

        method structure ?(indent = Some 0) ?wrap structureItems =
          (* We don't have any way to know if an extension is placed at the top
             level by the parsetree while there's a difference syntactically (%
             for structure_items/expressons and %% for top_level). This small fn
             detects this particular case (structure > structure_item >
             extension > value) and prints with double % *)
          let structure_item item =
            match item.pstr_desc with
            | Pstr_extension ((extension, PStr [ item ]), attrs) ->
              (match item.pstr_desc with
              (* In case of a value or `external`, the extension gets inlined
                 `let%private a = 1` *)
              | Pstr_value (rf, vb_list) ->
                self#bindings ~extension (rf, vb_list)
              | Pstr_primitive vd -> self#primitive_declaration ~extension vd
              | Pstr_module binding ->
                let bindingName =
                  atom ~loc:binding.pmb_name.loc (moduleIdent binding.pmb_name)
                in
                let module_binding =
                  let prefix = add_extension_sugar "module" (Some extension) in
                  self#let_module_binding prefix bindingName binding.pmb_expr
                in
                self#attach_std_item_attrs binding.pmb_attributes module_binding
              | Pstr_recmodule decls -> self#recmodule ~extension decls
              | Pstr_open od -> self#pstr_open ~extension od
              | Pstr_type (rf, l) -> self#type_def_list ~extension rf l
              | Pstr_typext te -> self#type_extension ~extension te
              | Pstr_eval
                  ( ({ pexp_desc =
                         Pexp_constant (Pconst_string (i, _, Some delim))
                     ; pexp_attributes
                     ; _
                     } as expr)
                  , _ ) ->
                let { Reason_attributes.stylisticAttrs; _ } =
                  Reason_attributes.partitionAttributes
                    ~allowUncurry:(Reason_heuristics.bsExprCanBeUncurried expr)
                    pexp_attributes
                in
                if Reason_attributes.has_quoted_extension_attrs stylisticAttrs
                then quoted_ext ~pct:"%%" extension i delim
                else
                  self#attach_std_item_attrs
                    attrs
                    (self#payload "%%" extension (PStr [ item ]))
              | _ ->
                self#attach_std_item_attrs
                  attrs
                  (self#payload "%%" extension (PStr [ item ])))
            | _ -> self#structure_item item
          in
          match structureItems with
          | [] -> makeList ?wrap []
          | first :: _ as structureItems ->
            let last =
              match List.rev structureItems with
              | last :: _ -> last
              | [] -> assert false
            in
            let loc_start = first.pstr_loc.loc_start in
            let loc_end = last.pstr_loc.loc_end in
            let items =
              groupAndPrint
                ~xf:structure_item
                ~getLoc:(fun x -> x.pstr_loc)
                ~comments:self#comments
                structureItems
            in
            source_map
              ~loc:{ loc_start; loc_end; loc_ghost = false }
              (makeList
                 ~postSpace:true
                 ~break:Always_rec
                 ?wrap
                 ?indent
                 ~inline:(true, false)
                 ~sep:(SepFinal (";", ";"))
                 items)

        (* How do modules become parsed?
         * let module (X: sig) = blah;
         *   Will not parse! (Should just make it parse to let [X:sig =]).
         * let module X: sig = blah;
         *   Becomes Pmod_constraint
         * let module X: sig = (blah:sig);
         *   Becomes Pmod_constraint .. Pmod_constraint
         * let module X = blah:typ;
         *   Becomes Pmod_constraint
         * let module X (Y:y) (Z:z):r => Q
         *   Becomes Pmod_functor...=> Pmod_constraint

         * let module X (Y:y) (Z:z):r => (Q:r2)
         *   Probably becomes Pmod_functor...=> (Pmod_constraint..
         *   Pmod_constraint)

         * let (module X) =
         *   Is a *completely* different thing (unpacking/packing first class modules).
         *   We should make sure this is very well distinguished.
         *   - Just replace all "let module" with a new three letter keyword (mod)?
         *   - Reserve let (module X) for unpacking first class modules.

         * See the notes about how Ppat_constraint become parsed and attempt to unify
         * those as well.
        *)

        method let_module_binding prefixText bindingName moduleExpr =
          let { Reason_attributes.stdAttrs; _ } =
            Reason_attributes.partitionAttributes moduleExpr.pmod_attributes
          in
          let argsList, return =
            self#curriedFunctorPatternsAndReturnStruct moduleExpr
          in
          match argsList, return.pmod_desc with
          (* Simple module with type constraint, no functor args. *)
          | [], Pmod_constraint (unconstrainedRetTerm, ct) ->
            let letPattern =
              makeList
                [ makeList ~postSpace:true [ atom prefixText; bindingName ]
                ; atom ":"
                ]
            in
            let typeConstraint = self#module_type letPattern ct in
            let includingEqual =
              makeList ~postSpace:true [ typeConstraint; atom "=" ]
            in
            formatAttachmentApplication
              applicationFinalWrapping
              (Some (true, includingEqual))
              ( [ self#moduleExpressionToFormattedApplicationItems
                    unconstrainedRetTerm
                  |> self#attach_std_item_attrs stdAttrs
                ]
              , None )
          (* Simple module with type no constraint, no functor args. *)
          | [], _ ->
            self#formatSimplePatternBinding
              prefixText
              bindingName
              None
              ( [ self#moduleExpressionToFormattedApplicationItems return
                  |> self#attach_std_item_attrs stdAttrs
                ]
              , None )
          | _, _ ->
            (* A functor *)
            let argsWithConstraint, actualReturn =
              match return.pmod_desc with
              (* A functor with constrained return type:
               *
               * let module X = (A) (B) : Ret => ...
               * *)
              | Pmod_constraint (me, ct) ->
                ( [ makeTup argsList
                  ; self#non_arrowed_module_type (atom ":") ct
                  ]
                , me )
              | _ -> [ makeTup argsList ], return
            in
            self#wrapCurriedFunctionBinding
              prefixText
              ~arrow:"=>"
              (makeList [ bindingName; atom " =" ])
              argsWithConstraint
              ( [ self#moduleExpressionToFormattedApplicationItems actualReturn
                  |> self#attach_std_item_attrs stdAttrs
                ]
              , None )

        method class_opening class_keyword name pci_virt ls =
          let firstToken = if class_keyword then "class" else "and" in
          match pci_virt, ls with
          (* When no class params, it's a very simple formatting for the
           * opener - no breaking.
          *)
          | Virtual, [] -> firstToken, atom "virtual", [ atom name ]
          | Concrete, [] -> firstToken, atom name, []
          | Virtual, _ :: _ ->
            firstToken, atom "virtual", [ atom name; self#class_params_def ls ]
          | Concrete, _ :: _ ->
            firstToken, atom name, [ self#class_params_def ls ]

        (* TODO: TODOATTRIBUTES: Structure items don't have attributes, but each
           pstr_desc *)
        method structure_item term =
          let item =
            match term.pstr_desc with
            | Pstr_eval (e, attrs) ->
              let { Reason_attributes.stdAttrs; jsxAttrs; uncurried; _ } =
                Reason_attributes.partitionAttributes attrs
              in
              if uncurried then Hashtbl.add uncurriedTable e.pexp_loc true;
              let layout =
                self#attach_std_item_attrs
                  stdAttrs
                  (self#unparseUnattributedExpr e)
              in
              (* If there was a JSX attribute BUT JSX component wasn't detected,
                 that JSX attribute needs to be pretty printed so it doesn't get
                 lost *)
              (match jsxAttrs with
              | [] -> layout
              | _ :: _ ->
                let jsxAttrNodes = List.map self#attribute jsxAttrs in
                makeList ~sep:(Sep " ") (jsxAttrNodes @ [ layout ]))
            | Pstr_type (_, []) -> assert false
            | Pstr_type (rf, l) -> self#type_def_list rf l
            | Pstr_value (rf, l) -> self#bindings (rf, l)
            | Pstr_typext te -> self#type_extension te
            | Pstr_exception ed ->
              self#exception_declaration
                { ed.ptyexn_constructor with
                  pext_attributes =
                    ed.ptyexn_attributes @ ed.ptyexn_constructor.pext_attributes
                }
            | Pstr_module binding ->
              let bindingName =
                atom ~loc:binding.pmb_name.loc (moduleIdent binding.pmb_name)
              in
              let module_binding =
                self#let_module_binding "module" bindingName binding.pmb_expr
              in
              self#attach_std_item_attrs binding.pmb_attributes module_binding
            | Pstr_open od -> self#pstr_open od
            | Pstr_modtype x ->
              let name = atom x.pmtd_name.txt in
              let letPattern =
                makeList ~postSpace:true [ atom "module type"; name; atom "=" ]
              in
              let main =
                match x.pmtd_type with
                | None -> makeList ~postSpace:true [ atom "module type"; name ]
                | Some mt -> self#module_type letPattern mt
              in
              self#attach_std_item_attrs x.pmtd_attributes main
            | Pstr_class l -> self#class_declaration_list l
            | Pstr_class_type l -> self#class_type_declaration_list l
            | Pstr_primitive vd -> self#primitive_declaration vd
            | Pstr_include incl ->
              self#attach_std_item_attrs incl.pincl_attributes
              @@
              (* Kind of a hack *)
              let moduleExpr = incl.pincl_mod in
              self#moduleExpressionToFormattedApplicationItems
                ~prefix:"include"
                moduleExpr
            | Pstr_recmodule decls -> self#recmodule decls
            | Pstr_attribute a -> self#floating_attribute a
            | Pstr_extension (((_extension, PStr []) as extension), attrs) ->
              (* Extension with attributes and without PStr gets printed
                 inline *)
              self#attach_std_attrs attrs (self#item_extension extension)
            | Pstr_extension ((extension, PStr [ item ]), attrs) ->
              (match item.pstr_desc with
              (* In case of a value, the extension gets inlined `let%lwt a =
                 1` *)
              | Pstr_value (rf, l) -> self#bindings ~extension (rf, l)
              | _ ->
                let { Reason_attributes.stdAttrs; docAttrs; _ } =
                  Reason_attributes.partitionAttributes ~partDoc:true attrs
                in
                let item = self#structure_item item in
                let layout =
                  self#attach_std_item_attrs ~extension stdAttrs item
                in
                makeList (List.map self#attribute docAttrs @ [ layout ]))
            | Pstr_extension (e, a) ->
              (* Notice how extensions have attributes - but not every structure
                 item does. *)
              self#attach_std_item_attrs a (self#item_extension e)
          in
          source_map ~loc:term.pstr_loc item

        method type_extension ?extension te =
          let formatOneTypeExtStandard prepend ({ ptyext_path; _ } as te) =
            let name = self#longident_loc ptyext_path in
            let item = self#formatOneTypeExt prepend name (atom "+=") te in
            let { Reason_attributes.stdAttrs; docAttrs; _ } =
              Reason_attributes.partitionAttributes
                ~partDoc:true
                te.ptyext_attributes
            in
            let layout = self#attach_std_item_attrs stdAttrs item in
            self#attachDocAttrsToLayout
              ~stdAttrs
              ~docAttrs
              ~loc:ptyext_path.loc
              ~layout
              ()
          in
          let label = add_extension_sugar "type" extension in
          formatOneTypeExtStandard (atom label) te

        (* [allowUnguardedSequenceBodies] allows sequence expressions {} to the
           right of `=>` to not be guarded in `{}` braces. *)
        method case_list ?(allowUnguardedSequenceBodies = false) l =
          let rec appendLabelToLast items rhs =
            match items with
            | hd :: [] -> label ~indent:0 ~space:true hd rhs :: []
            | hd :: tl -> hd :: appendLabelToLast tl rhs
            | [] -> raise (NotPossible "Cannot append to last of nothing")
          in

          let case_row { pc_lhs; pc_guard; pc_rhs } =
            let theOrs = orList pc_lhs in

            (* match x with *)
            (* | AnotherReallyLongVariantName (_, _, _)   *)
            (* | AnotherReallyLongVariantName2 (_, _, _) when true => { *)

            (* } *)

            (*<sbi><X>match x with</X>   *)
            (*     <Y>everythingElse</Y> *)
            (*</sbi>                     *)

            (*     ............................................................
             * :    each or segment has a spaced list <> that ties its    :
             * : bar "|" to its pattern                                   :
             * ...:..........................................................:.....
             * :  :  each or-patterned match is grouped in SpacedBreakableInline  :
             * :  :                                                          :    :
             * v  v                                                          v    v
             * <sbi><>|<lb><A><>     FirstThingStandalone t =></A></><B>t</B></lb></></sbi>
             * <sbi><>|<C>           AnotherReallyLongVariantName (_, _, _)</C></>
             * ^    <>|<lb><><lb><D>AnotherReallyLongVariantNam2 (_, _, _)</D>             (label the last in or ptn for or and label it again for arrow)
             * :        ^  ^   ^     <E>when true<E></lb> =></><F>{
             * :        :  :   :    </F>}</lb></sbi> ^       ^
             * :        :  :   :            ^     ^   :      :
             * :        :  :   :            :     :   :      :
             * :        :  :   :If there is :a WHERE  :      :
             * :        :  :   :an extra    :label is :      :
             * :        :  :   :inserted bef:ore the  :      :
             * :        :  :   :arrow.      :     :   :      :
             * :        :  :   :............:.....:...:      :
             * :        :  :                :     :          :
             * :        :  :                :     :          :
             * :        :  :                :     :          :
             * :        :  :The left side of:this final label:
             * :        :  :uses a list to  :append the arrow:
             * :        :  :................:.....:..........:
             * :        :                   :     :
             * :        :                   :     :
             * :        :                   :     :
             * :        :Final or segment is:     :
             * :        :wrapped in lbl that:     :
             * :        :partitions pattern :     :
             * :        :and arrow from     :     :
             * :        :expression.        :     :
             * :        :                   :     :
             * :        :...................:     :
             * :     [orsWithWhereAndArrowOnLast] :
             * :                                  :
             * :..................................:
             *             [row]
            *)
            let bar xx = makeList ~postSpace:true [ atom "|"; xx ] in
            let appendWhereAndArrow p =
              match pc_guard with
              | None -> makeList ~postSpace:true [ p; atom "=>" ]
              | Some g ->
                (* when x should break as a whole - extra list added around it
                   to make it break as one *)
                let withWhen =
                  label
                    ~space:true
                    p
                    (makeList
                       ~break:Layout.Never
                       ~inline:(true, true)
                       ~postSpace:true
                       [ label ~space:true (atom "when") (self#unparseExpr g) ])
                in
                makeList
                  ~inline:(true, true)
                  ~postSpace:true
                  [ withWhen; atom "=>" ]
            in
            let rec appendWhereAndArrowToLastOr = function
              | [] -> []
              | hd :: tl ->
                let formattedHd = self#pattern hd in
                let formattedHd =
                  match hd.ppat_desc with
                  | Ppat_constraint _ -> formatPrecedence formattedHd
                  | _ -> formattedHd
                in
                let formattedHd =
                  if tl == []
                  then appendWhereAndArrow formattedHd
                  else formattedHd
                in
                formattedHd :: appendWhereAndArrowToLastOr tl
            in
            let orsWithWhereAndArrowOnLast =
              appendWhereAndArrowToLastOr theOrs
            in
            let rhs =
              if allowUnguardedSequenceBodies
              then
                match self#under_pipe#letList pc_rhs with
                (* TODO: Still render a list with located information here so
                   that comments (eol) are interleaved *)
                | [ hd ] -> hd
                (* In this case, we don't need any additional indentation,
                   because there aren't wrapping {} which would cause zero
                   indentation to look strange. *)
                | lst -> makeUnguardedLetSequence lst
              else self#under_pipe#unparseExpr pc_rhs
            in
            source_map
            (* Fake shift the location to accommodate for the bar, to make sure
               * the wrong comments don't make their way past the next bar. *)
              ~loc:
                (expandLocation
                   ~expand:(0, 0)
                   { loc_start = pc_lhs.ppat_loc.loc_start
                   ; loc_end = pc_rhs.pexp_loc.loc_end
                   ; loc_ghost = false
                   })
              (makeList
                 ~break:Always_rec
                 ~inline:(true, true)
                 (List.map
                    bar
                    (appendLabelToLast orsWithWhereAndArrowOnLast rhs)))
          in
          groupAndPrint
            ~xf:case_row
            ~getLoc:(fun { pc_lhs; pc_rhs; _ } ->
              { pc_lhs.ppat_loc with loc_end = pc_rhs.pexp_loc.loc_end })
            ~comments:self#comments
            l

        (* Formats a list of a single expr param in such a way that the parens of the function or
         * (poly)-variant application and the wrapping of the param stick together when the layout breaks.
         *  Example: `foo({a: 1, b: 2})` needs to be formatted as
         *  foo({
         *    a: 1,
         *    b: 2
         *  })
         *  when the line length dictates breaking. Notice how `({` and `})` 'hug'.
         *  Also see "isSingleArgParenApplication" which determines if
         *  this kind of formatting should happen. *)
        method singleArgParenApplication
          ?(wrap = "", "")
          ?(uncurried = false)
          es =
          let lwrap, rwrap = wrap in
          let lparen = lwrap ^ if uncurried then "(. " else "(" in
          let rparen = ")" ^ rwrap in
          match es with
          | [ { pexp_attributes = []; pexp_desc = Pexp_record (l, eo); _ } ] ->
            self#unparseRecord ~wrap:(lparen, rparen) l eo
          | [ { pexp_attributes = []; pexp_desc = Pexp_tuple l; _ } ] ->
            self#unparseSequence ~wrap:(lparen, rparen) ~construct:`Tuple l
          | [ { pexp_attributes = []; pexp_desc = Pexp_array l; _ } ] ->
            self#unparseSequence ~wrap:(lparen, rparen) ~construct:`Array l
          | [ { pexp_attributes = []; pexp_desc = Pexp_object cs; _ } ] ->
            self#classStructure ~wrap:(lparen, rparen) cs
          | [ { pexp_attributes = []; pexp_desc = Pexp_extension (s, p); _ } ]
            when s.txt = "mel.obj" ->
            self#formatBsObjExtensionSugar ~wrap:(lparen, rparen) p
          | [ ({ pexp_attributes = []; _ } as exp) ]
            when is_simple_list_expr exp ->
            (match view_expr exp with
            | `list xs ->
              self#unparseSequence ~construct:`List ~wrap:(lparen, rparen) xs
            | `cons xs ->
              self#unparseSequence ~construct:`ES6List ~wrap:(lparen, rparen) xs
            | _ -> assert false)
          | _ -> assert false

        method formatSingleArgLabelApplication labelTerm rightExpr =
          let layout_right =
            match rightExpr with
            | { pexp_desc = Pexp_let _; _ } ->
              makeLetSequence ~wrap:("({", "})") (self#letList rightExpr)
            | e when isSingleArgParenApplication [ rightExpr ] ->
              self#singleArgParenApplication [ e ]
            | { pexp_desc = Pexp_construct ({ txt = Lident "()"; _ }, _); _ } ->
              (* special case unit such that we don't end up with double
                 parens *)
              self#simplifyUnparseExpr rightExpr
            | _ -> formatPrecedence (self#unparseExpr rightExpr)
          in
          label labelTerm layout_right

        method label_x_expression_param (l, e) =
          let term = self#unparseProtectedExpr e in
          let param =
            match l, e with
            | Nolabel, _ -> term
            | Labelled lbl, _
              when Reason_heuristics.is_punned_labelled_expression e lbl ->
              makeList [ atom namedArgSym; term ]
            | Optional lbl, _
              when Reason_heuristics.is_punned_labelled_expression e lbl ->
              makeList [ atom namedArgSym; label term (atom "?") ]
            | Labelled lbl, _ -> label (atom (namedArgSym ^ lbl ^ "=")) term
            | Optional lbl, _ -> label (atom (namedArgSym ^ lbl ^ "=?")) term
          in
          source_map ~loc:e.pexp_loc param

        method label_x_expression_params ?wrap ?(uncurried = false) xs =
          match xs with
          (* function applications with unit as only argument should be printed differently
           * e.g. print_newline(()) should be printed as print_newline() *)
          | [ ( Nolabel
              , { pexp_attributes = []
                ; pexp_desc = Pexp_construct ({ txt = Lident "()"; _ }, None)
                ; _
                } )
            ] ->
            makeList
              ~break:Never
              ?wrap
              [ (if uncurried then atom "(.)" else atom "()") ]
          (* The following cases provide special formatting when there's only one expr_param that is a tuple/array/list/record etc.
           *  e.g. foo({a: 1, b: 2})
           *  becomes ->
           *  foo({
           *    a: 1,
           *    b: 2,
           *  })
           *  when the line-length indicates breaking.
          *)
          | [ (Nolabel, exp) ] when isSingleArgParenApplication [ exp ] ->
            self#singleArgParenApplication ?wrap ~uncurried [ exp ]
          | params ->
            makeTup
              ?wrap
              ~uncurried
              (List.map self#label_x_expression_param params)

        (* Prefix represents an optional layout. When passed it will be "prefixed" to
         * the funExpr. Example, given `bar(x, y)` with prefix `foo`, we get
         * foobar(x,y). When the arguments break, the closing `)` is nicely aligned
         * on the height of the prefix:
         *  foobar(
         *    x,
         *    y,
         *  )  --> notice how `)` sits on the height of `foo` instead of `bar`
         *
         *  ~wrap -> represents optional "wrapping", might be useful in context of jsx
         *  where braces are required:
         * prop={bar(   -> `{` is formatted before the funExpr
         *   x,
         *   y,
         * )}      -> notice how the closing brace hugs: `)}`
        *)
        method formatFunAppl
          ?(prefix = atom "")
          ?(wrap = "", "")
          ~jsxAttrs
          ~args
          ~funExpr
          ~applicationExpr
          ?(uncurried = false)
          () =
          let leftWrap, rightWrap = wrap in
          let uncurriedApplication = uncurried in
          (* If there was a JSX attribute BUT JSX component wasn't detected,
             that JSX attribute needs to be pretty printed so it doesn't get
             lost *)
          let maybeJSXAttr = List.map self#attribute jsxAttrs in
          let categorizeFunApplArgs args =
            let reverseArgs = List.rev args in
            match reverseArgs with
            | ((_, { pexp_desc = Pexp_fun _; _ }) as callback) :: args
              when []
                   == List.filter
                        (fun (_, e) ->
                           match e.pexp_desc with
                           | Pexp_fun _ -> true
                           | _ -> false)
                        args
                   (* default to normal formatting if there's more than one
                      callback *)
              ->
              `LastArgIsCallback (callback, List.rev args)
            | _ -> `NormalFunAppl args
          in
          let formattedFunExpr =
            match funExpr.pexp_desc with
            (* pipe first chain or sharpop chain as funExpr, no parens needed,
               we know how to parse *)
            | Pexp_apply ({ pexp_desc = Pexp_ident { txt = Lident s; _ }; _ }, _)
              when requireNoSpaceFor s ->
              self#unparseExpr funExpr
            | Pexp_field _ -> self#unparseExpr funExpr
            | _ -> self#simplifyUnparseExpr funExpr
          in
          let formattedFunExpr =
            makeList [ prefix; atom leftWrap; formattedFunExpr ]
          in
          match categorizeFunApplArgs args with
          | `LastArgIsCallback (callbackArg, args) ->
            (* This is the following case:
             * Thing.map(foo, bar, baz, (abc, z) =>
             *   MyModuleBlah.toList(argument)
            *)
            let argLbl, cb = callbackArg in
            let { Reason_attributes.stdAttrs; uncurried; _ } =
              Reason_attributes.partitionAttributes cb.pexp_attributes
            in
            let cbAttrs = stdAttrs in
            if uncurried then Hashtbl.add uncurriedTable cb.pexp_loc true;
            let cbArgs, retCb =
              self#curriedPatternsAndReturnVal { cb with pexp_attributes = [] }
            in
            let cbArgs =
              if cbAttrs != []
              then
                makeList
                  ~break:IfNeed
                  ~inline:(true, true)
                  ~postSpace:true
                  (List.map self#attribute cbAttrs @ cbArgs)
              else makeList cbArgs
            in
            let retCb, cbArgs =
              match retCb.pexp_desc with
              | Pexp_constraint (a, t) ->
                a, makeList [ cbArgs; atom ": "; self#core_type t ]
              | _ -> retCb, cbArgs
            in
            let theCallbackArg =
              match argLbl with
              | Optional s ->
                makeList ([ atom namedArgSym; atom s; atom "=?" ] @ [ cbArgs ])
              | Labelled s ->
                makeList ([ atom namedArgSym; atom s; atom "=" ] @ [ cbArgs ])
              | Nolabel -> cbArgs
            in
            let theFunc =
              source_map
                ~loc:funExpr.pexp_loc
                (makeList
                   ~wrap:("", if uncurriedApplication then "(." else "(")
                   [ formattedFunExpr ])
            in
            let formattedFunAppl =
              match self#letList retCb with
              | [ x ] ->
                (* force breaks for test assertion style callbacks, e.g.
                 *  describe("App", () => test("math", () => Expect.expect(1 + 2) |> toBe(3)));
                 * should always break for readability of the tests:
                 *  describe("App", () =>
                 *    test("math", () =>
                 *      Expect.expect(1 + 2) |> toBe(3)
                 *    )
                 *  );
                *)
                let forceBreak =
                  match funExpr.pexp_desc with
                  | Pexp_ident ident
                    when let lastIdent = Longident.last_exn ident.txt in
                         List.mem
                           lastIdent
                           [ "test"; "describe"; "it"; "expect" ] ->
                    true
                  | _ -> false
                in
                let ((leftWrap, rightWrap) as wrap) = "=> ", ")" ^ rightWrap in
                let wrap =
                  if self#should_preserve_requested_braces retCb
                  then leftWrap ^ "{", "}" ^ rightWrap
                  else wrap
                in
                let returnValueCallback =
                  makeList
                    ~break:(if forceBreak then Always else IfNeed)
                    ~wrap
                    [ x ]
                in
                let argsWithCallbackArgs =
                  List.concat
                    [ List.map self#label_x_expression_param args
                    ; [ theCallbackArg ]
                    ]
                in
                let left =
                  label
                    theFunc
                    (makeList
                       ~pad:(uncurriedApplication, false)
                       ~wrap:("", " ")
                       ~break:IfNeed
                       ~inline:(true, true)
                       ~sep:(Sep ",")
                       ~postSpace:true
                       argsWithCallbackArgs)
                in
                label left returnValueCallback
              | xs ->
                let printWidthExceeded =
                  Reason_heuristics.funAppCallbackExceedsWidth
                    ~printWidth:settings.width
                    ~args
                    ~funExpr
                    ()
                in
                if not printWidthExceeded
                then
                  (* Thing.map(foo, bar, baz, (abc, z) =>
                   *   MyModuleBlah.toList(argument)
                   * )
                   *
                   * To get this kind of formatting we need to construct the following tree:
                   * <Label>
                   * <left>Thing.map(foo, bar, baz, (abc, z)</left><right>=>
                   *   MyModuleBlah.toList(argument)
                   * )</right>
                   * </Label>
                   *
                   * where left is
                   * <Label><left>Thing.map(</left></right>foo, bar, baz, (abc, z) </right></Label>
                   *
                   * The <right> part of that label could be a <List> with wrap:("", " ") break:IfNeed inline:(true, true)
                   * with items: "foo", "bar", "baz", "(abc, z)", separated by commas.
                   *
                   * this is also necessary to achieve the following formatting where }) hugs :
                   * test("my test", () => {
                   *   let x = a + b;
                   *   let y = z + c;
                   *   x + y
                   * });
                  *)
                  let ((leftWrap, rightWrap) as wrap) =
                    "=> ", ")" ^ rightWrap
                  in
                  let wrap =
                    match
                      ( self#should_preserve_requested_braces retCb
                      , self#isSeriesOfOpensFollowedByNonSequencyExpression
                          { retCb with pexp_attributes = [] } )
                    with
                    | true, _ | _, false -> leftWrap ^ "{", "}" ^ rightWrap
                    | _ -> wrap
                  in
                  let right =
                    source_map
                      ~loc:retCb.pexp_loc
                      (makeList
                         ~break:Always_rec
                         ~wrap
                         ~sep:(SepFinal (";", ";"))
                         xs)
                  in
                  let argsWithCallbackArgs =
                    List.map self#label_x_expression_param args
                    @ [ theCallbackArg ]
                  in
                  let left =
                    label
                      theFunc
                      (makeList
                         ~wrap:("", " ")
                         ~break:IfNeed
                         ~inline:(true, true)
                         ~sep:(Sep ",")
                         ~postSpace:true
                         argsWithCallbackArgs)
                  in
                  label left right
                else
                  (* Since the heuristic says the line length is exceeded in this case,
                   * we conveniently format everything as
                   * <label><left>Thing.map(</left><right><list>
                   *   foo,
                   *   bar,
                   *   baz,
                   *   <label> <left>(abc) =></left> <right><list> {
                   *     let x = 1;
                   *     let y = 2;
                   *     x + y
                   *   }</list></right></label>
                   * )</list></right></label>
                  *)
                  let args =
                    makeList
                      ~break:Always
                      ~wrap:("", ")" ^ rightWrap)
                      ~sep:commaTrail
                      (List.map self#label_x_expression_param args
                      @ [ label
                            ~space:true
                            (makeList ~wrap:("", " =>") [ theCallbackArg ])
                            (source_map
                               ~loc:retCb.pexp_loc
                               (makeLetSequence xs))
                        ])
                  in
                  (* This will need to be (theFunc, args) *)
                  label theFunc args
            in
            maybeJSXAttr @ [ formattedFunAppl ]
          | `NormalFunAppl args ->
            let theFunc = source_map ~loc:funExpr.pexp_loc formattedFunExpr in
            (* reset here only because [function,match,try,sequence] are lower
               priority *)
            (* The "expression location" might be different than the location of the actual
             * function application because things like surrounding { } expand the
             * parsed location (in body of while loop for example).
             * We recover the most meaningful function application location we can.*)
            let syntheticApplicationLocation, syntheticArgLoc =
              match args with
              | [] -> funExpr.pexp_loc, funExpr.pexp_loc
              | _ :: _ ->
                ( { funExpr.pexp_loc with
                    loc_end = applicationExpr.pexp_loc.loc_end
                  }
                , { funExpr.pexp_loc with
                    loc_start = funExpr.pexp_loc.loc_end
                  ; loc_end = applicationExpr.pexp_loc.loc_end
                  } )
            in
            let theArgs =
              self#reset#label_x_expression_params
                ~wrap:("", rightWrap)
                ~uncurried
                args
            in
            maybeJSXAttr
            @ [ source_map
                  ~loc:syntheticApplicationLocation
                  (label theFunc (source_map ~loc:syntheticArgLoc theArgs))
              ]
      end

    let toplevel_phrase ppf x =
      match x with
      | Ptop_def s -> format_layout ppf (printer#structure s)
      | Ptop_dir _ -> print_string "(* top directives not supported *)"

    let case_list ppf x = List.iter (format_layout ppf) (printer#case_list x)

    (* Convert a Longident to a list of strings. E.g. M.Constructor will be
       ["Constructor"; "M.Constructor"] Also support ".Constructor" to specify
       access without a path. *)
    let longident_for_arity lid =
      let rec toplevel = function
        | Lident s -> [ s ]
        | Ldot (lid, s) ->
          let append_s x = x ^ "." ^ s in
          s :: List.map append_s (toplevel lid)
        | Lapply (_, s) -> toplevel s
      in
      match lid with Lident s -> ("." ^ s) :: toplevel lid | _ -> toplevel lid

    (* add expilcit_arity to a list of attributes *)
    let add_explicit_arity loc attributes =
      { attr_name = { txt = "explicit_arity"; loc }
      ; attr_payload = PStr []
      ; attr_loc = loc
      }
      :: Reason_syntax_util.normalized_attributes "explicit_arity" attributes

    (* explicit_arity_exists check if expilcit_arity exists *)
    let explicit_arity_not_exists attributes =
      not (Reason_syntax_util.attribute_exists "explicit_arity" attributes)

    (* wrap_expr_with_tuple wraps an expression
     * with tuple as a sole argument.
    *)
    let wrap_expr_with_tuple exp = { exp with pexp_desc = Pexp_tuple [ exp ] }

    (* wrap_pat_with_tuple wraps an pattern
     * with tuple as a sole argument.
    *)
    let wrap_pat_with_tuple pat = { pat with ppat_desc = Ppat_tuple [ pat ] }

    (* explicit_arity_constructors is a set of constructors that are known to have
     * multiple arguments
     *
    *)

    module StringSet = Stdlib.Set.Make (String)

    let built_in_explicit_arity_constructors =
      [ "Some"; "Assert_failure"; "Match_failure" ]

    let explicit_arity_constructors =
      StringSet.of_list
        (built_in_explicit_arity_constructors
        @ !configuredSettings.constructorLists)

    let preprocessing_mapper =
      let escape_slashes = new Reason_syntax_util.escape_stars_slashes_mapper in
      object
        inherit Ast_traverse.map as super

        method! expression expr =
          let expr =
            match expr with
            | { pexp_desc = Pexp_construct (lid, Some sp)
              ; pexp_loc
              ; pexp_attributes
              ; _
              }
              when List.exists
                     (fun c -> StringSet.mem c explicit_arity_constructors)
                     (longident_for_arity lid.txt)
                   && explicit_arity_not_exists pexp_attributes ->
              { pexp_desc = Pexp_construct (lid, Some (wrap_expr_with_tuple sp))
              ; pexp_loc
              ; pexp_attributes = add_explicit_arity pexp_loc pexp_attributes
              ; pexp_loc_stack = []
              }
            | x -> x
          in
          escape_slashes#expression (super#expression expr)

        method! pattern pat =
          let pat =
            match pat with
            | { ppat_desc = Ppat_construct (lid, Some (x, sp))
              ; ppat_loc
              ; ppat_attributes
              ; _
              }
              when List.exists
                     (fun c -> StringSet.mem c explicit_arity_constructors)
                     (longident_for_arity lid.txt)
                   && explicit_arity_not_exists ppat_attributes ->
              { ppat_desc =
                  Ppat_construct (lid, Some (x, wrap_pat_with_tuple sp))
              ; ppat_loc
              ; ppat_attributes = add_explicit_arity ppat_loc ppat_attributes
              ; ppat_loc_stack = []
              }
            | x -> x
          in
          escape_slashes#pattern (super#pattern pat)
      end

    let ml_to_reason_swap_operator_mapper =
      new Reason_syntax_util.ml_to_reason_swap_operator_mapper

    let preprocessing_mapper f a =
      a |> f ml_to_reason_swap_operator_mapper |> f preprocessing_mapper

    let core_type ppf x =
      format_layout
        ppf
        (printer#core_type
           (preprocessing_mapper Reason_syntax_util.apply_mapper_to_type x))

    let pattern ppf x =
      format_layout
        ppf
        (printer#pattern
           (preprocessing_mapper Reason_syntax_util.apply_mapper_to_pattern x))

    let signature (comments : Comment.t list) ppf x =
      List.iter (fun comment -> printer#trackComment comment) comments;
      format_layout
        ppf
        ~comments
        (printer#signature
           (preprocessing_mapper Reason_syntax_util.apply_mapper_to_signature x))

    let structure (comments : Comment.t list) ppf x =
      List.iter (fun comment -> printer#trackComment comment) comments;
      format_layout
        ppf
        ~comments
        (printer#structure
           (preprocessing_mapper Reason_syntax_util.apply_mapper_to_structure x))

    let expression ppf x =
      format_layout
        ppf
        (printer#unparseExpr
           (preprocessing_mapper Reason_syntax_util.apply_mapper_to_expr x))

    let case_list = case_list
  end
  in
  object
    method core_type = Formatter.core_type
    method pattern = Formatter.pattern
    method signature = Formatter.signature
    method structure = Formatter.structure

    (* For merlin-destruct *)
    method toplevel_phrase = Formatter.toplevel_phrase
    method expression = Formatter.expression
    method case_list = Formatter.case_list
  end
