@ ProgramNode (location: (1,0)-(3,3))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(3,3))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ WhileNode (location: (1,0)-(3,3))
            ├── flags: newline
            ├── keyword_loc: (1,0)-(1,5) = "while"
            ├── do_keyword_loc: ∅
            ├── closing_loc: (3,0)-(3,3) = "end"
            ├── predicate:
            │   @ CallNode (location: (1,6)-(1,18))
            │   ├── flags: ∅
            │   ├── receiver:
            │   │   @ CallNode (location: (1,10)-(1,18))
            │   │   ├── flags: ∅
            │   │   ├── receiver:
            │   │   │   @ CallNode (location: (1,10)-(1,13))
            │   │   │   ├── flags: variable_call, ignore_visibility
            │   │   │   ├── receiver: ∅
            │   │   │   ├── call_operator_loc: ∅
            │   │   │   ├── name: :var
            │   │   │   ├── message_loc: (1,10)-(1,13) = "var"
            │   │   │   ├── opening_loc: ∅
            │   │   │   ├── arguments: ∅
            │   │   │   ├── closing_loc: ∅
            │   │   │   └── block: ∅
            │   │   ├── call_operator_loc: (1,13)-(1,14) = "."
            │   │   ├── name: :nil?
            │   │   ├── message_loc: (1,14)-(1,18) = "nil?"
            │   │   ├── opening_loc: ∅
            │   │   ├── arguments: ∅
            │   │   ├── closing_loc: ∅
            │   │   └── block: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :!
            │   ├── message_loc: (1,6)-(1,9) = "not"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            └── statements:
                @ StatementsNode (location: (2,2)-(2,7))
                ├── flags: ∅
                └── body: (length: 1)
                    └── @ StringNode (location: (2,2)-(2,7))
                        ├── flags: newline
                        ├── opening_loc: (2,2)-(2,3) = "'"
                        ├── content_loc: (2,3)-(2,6) = "foo"
                        ├── closing_loc: (2,6)-(2,7) = "'"
                        └── unescaped: "foo"
