@ ProgramNode (location: (0...4))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...4))
    └── body: (length: 2)
        ├── @ CallNode (location: (0...1))
        │   ├── receiver: ∅
        │   ├── call_operator_loc: ∅
        │   ├── message_loc: (0...1) = "a"
        │   ├── opening_loc: ∅
        │   ├── arguments: ∅
        │   ├── closing_loc: ∅
        │   ├── block: ∅
        │   ├── flags: variable_call
        │   └── name: "a"
        └── @ CallNode (location: (3...4))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (3...4) = "b"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: variable_call
            └── name: "b"
