@ ProgramNode (location: (6...34))
├── locals: [:foo]
└── statements:
    @ StatementsNode (location: (6...34))
    └── body: (length: 2)
        ├── @ LocalVariableOperatorWriteNode (location: (6...24))
        │   ├── name_loc: (6...9) = "foo"
        │   ├── operator_loc: (10...12) = "+="
        │   ├── value:
        │   │   @ CallNode (location: (21...24))
        │   │   ├── receiver: ∅
        │   │   ├── call_operator_loc: ∅
        │   │   ├── message_loc: (21...24) = "bar"
        │   │   ├── opening_loc: ∅
        │   │   ├── arguments: ∅
        │   │   ├── closing_loc: ∅
        │   │   ├── block: ∅
        │   │   ├── flags: variable_call
        │   │   └── name: "bar"
        │   ├── name: :foo
        │   ├── operator: :+
        │   └── depth: 0
        └── @ CallNode (location: (31...34))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (31...34) = "baz"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: variable_call
            └── name: "baz"
