@ ProgramNode (location: (1,0)-(1,10))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,10))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,10))
            ├── flags: ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :fun
            ├── message_loc: (1,0)-(1,3) = "fun"
            ├── opening_loc: (1,3)-(1,4) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (1,4)-(1,9))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ CallNode (location: (1,4)-(1,9))
            │           ├── flags: ignore_visibility
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── name: :f
            │           ├── message_loc: (1,4)-(1,5) = "f"
            │           ├── opening_loc: ∅
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (1,6)-(1,9))
            │           │   ├── flags: ∅
            │           │   └── arguments: (length: 1)
            │           │       └── @ CallNode (location: (1,6)-(1,9))
            │           │           ├── flags: variable_call, ignore_visibility
            │           │           ├── receiver: ∅
            │           │           ├── call_operator_loc: ∅
            │           │           ├── name: :bar
            │           │           ├── message_loc: (1,6)-(1,9) = "bar"
            │           │           ├── opening_loc: ∅
            │           │           ├── arguments: ∅
            │           │           ├── closing_loc: ∅
            │           │           └── block: ∅
            │           ├── closing_loc: ∅
            │           └── block: ∅
            ├── closing_loc: (1,9)-(1,10) = ")"
            └── block: ∅