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