Kakoune design
==============

This document describes the design goals for Kakoune, including rationale.

Interactivity
-------------

Unlike Vim, Kakoune does not have an underlying line-oriented editor. It is
always expected to be used in an interactive fashion, displaying edited text in
real time. That should not prevent Kakoune from being used non-interactively
(executing a macro for example), but priority should be given to ease of
interactive use.

Limited scope
-------------

Kakoune is a code editor. It is not an IDE, not a file browser, not a word
processor and not a window manager. It should be very efficient at editing code.
As a side effect, it should be very efficient at editing text in general.

Composability
-------------

Being limited in scope to code editing should not isolate Kakoune from its
environment. On the contrary, Kakoune is expected to run on a Unix-like
system alongside a lot of text-based tools, and should make it easy to
interact with these tools.

For example, sorting lines should be done using the Unix sort command, not
with an internal implementation. Kakoune should make it easy to do that,
hence the +|+ command for piping selected text through a filter.

The modern Unix environment is not limited to text filters. Most people use
a graphical interface nowadays, and Kakoune should be able to take advantage
of that without hindering text mode support. For example, Kakoune enables
multiple windows by supporting many clients on the same editing session,
not by reimplementing tiling and tabbing. Those responsibilities are left
to the system window manager.

Orthogonality
-------------

Kakoune features should be as orthogonal as possible. For example, in Vim,
there are many ways to modify the buffer: Through normal/insert
mode, command mode, and Vim scripts. In Kakoune, modifying the buffer is
only the job of normal/insert mode.

That means there should be clear separation of concerns between modes:

 * normal mode is for manipulating the selection and the selection contents.

 * insert mode is for interactive insertion into the buffer.

 * command mode is for non-editing features (opening a file, setting
   options...).

Orthogonality is an ideal; it should not forbid common sense pragmatism.
The +gf+ and +ga+ commands are not strictly selection manipulation commands,
but they do fit nicely with other +goto+ commands, so they are acceptable in
normal mode even though they could arguably be moved to command mode.

Modes should be orthogonal, as should commands within modes. For
example, Vim uses both +d+ and +x+ to delete text, with minor differences. In
Kakoune only +d+ exists, and the design ensures that +x+ is not needed.

Speed
-----

Kakoune should be fast -- fast to use, as in a lot of editing in a few
keystrokes, and fast to execute.

 * Vim is the benchmark here. Most editing tasks should be doable in fewer
   or the same number of keystrokes as Vim.

 * Kakoune is designed with asynchronicity in mind. Launching a background
   process and using its result when available should not block the editor.

 * Kakoune should be implemented with speed in mind. A slow editor is a
   useless one.

Simplicity
----------

Simplicity is nice. Simplicity correlates with orthogonality and speed. It makes
things easier to understand, bugs easier to fix, and code easier to change.

 * *No threading*: multithreading is a hard problem and is not well suited
   to a text editor:

   - When we want a direct result, we need to be synchronous with
     the user. A 4x speed improvement is meaningless; we need to have an
     algorithm which appears instantaneous to the user.

   - When we want an asynchronous result, the processing is best left
     to a helper command which can be reused with other Unix tools.

 * *No binary plugins*: shared objects by themselves add a lot of
   complexity. Plugins add another interface to Kakoune and go against
   orthogonality. The +%sh{ ... }+ and socket interfaces should be made good
   enough for most plugin use cases.
  
   - Rather than writing a plugin for intelligent code completion or source
     code navigation, it is better to write an independent helper tool that can
     interact with Kakoune through the shell.

 * *No integrated scripting language*: for the same reason as binary plugins.

 * *Limited smartness*: Kakoune should not try to be too smart. Being smart
   is often unpredictable for the user and makes things context-dependent.
   When Kakoune tries to be smart, it should provide the alternative,
   'non-smart' version. For instance, +\*+ tries to detect word boundaries on
   the selection, but +alt-*+ opts out of this behavior.

Unified interactive use and scripting
-------------------------------------

As an effect of both Orthogonality and Simplicity, normal mode is not
a layer of keys bound to a text editing language layer. Normal mode *is*
the text editing language.

That means there is no +delete-selected-text+ command that +d+ is bound
to. +d+ *is* the +delete selected text+ command.

This permits both scripting and interactive use cases to share the same text
editing language. Both use normal mode to express complex editing.

Besides promoting simplicity by avoiding the introduction of another
layer, this helps ensure the interactive editing language is expressive
enough to handle complex use cases, such as indentation hooks.

Language-agnostic
-----------------

Kakoune should not be tailored for writing in a specific programming
language. Support for different languages should be provided by a kak script
file. Built-in language support should be avoided.

Self-documenting
----------------

Kakoune should be able to document its features. Live documentation, along
with an extensive suggestion/completion system, provides the discoverability
which is often lacking in non-GUI tools. As much as possible, documentation
should be integrated with the code so that it stays up to date.

Vim compatibility
-----------------

Kakoune is inspired by Vim and should try to keep its commands similar to
Vim's if there are no compelling reasons to deviate. However, self-consistency
is more important than Vim compatibility.
