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