@ ProgramNode (location: (1,0)-(1,7))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,7))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,7))
            ├── flags: ∅
            ├── receiver:
            │   @ CallNode (location: (1,0)-(1,1))
            │   ├── flags: variable_call
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :a
            │   ├── message_loc: (1,0)-(1,1) = "a"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: (1,1)-(1,2) = "."
            ├── name: :f
            ├── message_loc: (1,2)-(1,3) = "f"
            ├── opening_loc: (1,3)-(1,4) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (1,4)-(1,5))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ IntegerNode (location: (1,4)-(1,5))
            │           └── flags: decimal
            ├── closing_loc: (1,6)-(1,7) = ")"
            └── block: ∅
