@ ProgramNode (location: (1,0)-(1,2))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,2))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,2))
            ├── flags: ∅
            ├── receiver:
            │   @ CallNode (location: (1,1)-(1,2))
            │   ├── flags: variable_call
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :a
            │   ├── message_loc: (1,1)-(1,2) = "a"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: ∅
            ├── name: :-@
            ├── message_loc: (1,0)-(1,1) = "-"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
