@ ProgramNode (location: (1,0)-(1,11))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,11))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,11))
            ├── flags: ∅
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :fun
            ├── message_loc: (1,0)-(1,3) = "fun"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (1,4)-(1,11))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ ParenthesesNode (location: (1,4)-(1,11))
            │           ├── body:
            │           │   @ StatementsNode (location: (1,5)-(1,10))
            │           │   └── body: (length: 1)
            │           │       └── @ CallNode (location: (1,5)-(1,10))
            │           │           ├── flags: ∅
            │           │           ├── receiver: ∅
            │           │           ├── call_operator_loc: ∅
            │           │           ├── name: :f
            │           │           ├── message_loc: (1,5)-(1,6) = "f"
            │           │           ├── opening_loc: ∅
            │           │           ├── arguments:
            │           │           │   @ ArgumentsNode (location: (1,7)-(1,10))
            │           │           │   ├── flags: ∅
            │           │           │   └── arguments: (length: 1)
            │           │           │       └── @ CallNode (location: (1,7)-(1,10))
            │           │           │           ├── flags: variable_call
            │           │           │           ├── receiver: ∅
            │           │           │           ├── call_operator_loc: ∅
            │           │           │           ├── name: :bar
            │           │           │           ├── message_loc: (1,7)-(1,10) = "bar"
            │           │           │           ├── opening_loc: ∅
            │           │           │           ├── arguments: ∅
            │           │           │           ├── closing_loc: ∅
            │           │           │           └── block: ∅
            │           │           ├── closing_loc: ∅
            │           │           └── block: ∅
            │           ├── opening_loc: (1,4)-(1,5) = "("
            │           └── closing_loc: (1,10)-(1,11) = ")"
            ├── closing_loc: ∅
            └── block: ∅
