@ ProgramNode (location: (0...23))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...23))
    └── body: (length: 1)
        └── @ WhileNode (location: (0...23))
            ├── keyword_loc: (0...5) = "while"
            ├── closing_loc: (20...23) = "end"
            ├── predicate:
            │   @ CallNode (location: (6...16))
            │   ├── receiver:
            │   │   @ ParenthesesNode (location: (10...16))
            │   │   ├── body:
            │   │   │   @ StatementsNode (location: (11...15))
            │   │   │   └── body: (length: 1)
            │   │   │       └── @ TrueNode (location: (11...15))
            │   │   ├── opening_loc: (10...11) = "("
            │   │   └── closing_loc: (15...16) = ")"
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (6...9) = "not"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: ∅
            │   └── name: "!"
            ├── statements: ∅
            └── flags: ∅
