@ ProgramNode (location: (0...12))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...12))
    └── body: (length: 1)
        └── @ CallNode (location: (0...12))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...3) = "fun"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (4...12))
            │   └── arguments: (length: 1)
            │       └── @ CallNode (location: (4...12))
            │           ├── receiver:
            │           │   @ ParenthesesNode (location: (4...7))
            │           │   ├── body:
            │           │   │   @ StatementsNode (location: (5...6))
            │           │   │   └── body: (length: 1)
            │           │   │       └── @ IntegerNode (location: (5...6))
            │           │   │           └── flags: decimal
            │           │   ├── opening_loc: (4...5) = "("
            │           │   └── closing_loc: (6...7) = ")"
            │           ├── call_operator_loc: (7...8) = "."
            │           ├── message_loc: (8...12) = "to_i"
            │           ├── opening_loc: ∅
            │           ├── arguments: ∅
            │           ├── closing_loc: ∅
            │           ├── block: ∅
            │           ├── flags: ∅
            │           └── name: "to_i"
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: ∅
            └── name: "fun"
