@ ProgramNode (location: (1,6)-(3,9))
├── locals: [:foo]
└── statements:
    @ StatementsNode (location: (1,6)-(3,9))
    └── body: (length: 2)
        ├── @ LocalVariableOperatorWriteNode (location: (1,6)-(2,11))
        │   ├── name_loc: (1,6)-(1,9) = "foo"
        │   ├── operator_loc: (1,10)-(1,12) = "+="
        │   ├── value:
        │   │   @ CallNode (location: (2,8)-(2,11))
        │   │   ├── flags: variable_call, ignore_visibility
        │   │   ├── receiver: ∅
        │   │   ├── call_operator_loc: ∅
        │   │   ├── name: :bar
        │   │   ├── message_loc: (2,8)-(2,11) = "bar"
        │   │   ├── opening_loc: ∅
        │   │   ├── arguments: ∅
        │   │   ├── closing_loc: ∅
        │   │   └── block: ∅
        │   ├── name: :foo
        │   ├── operator: :+
        │   └── depth: 0
        └── @ CallNode (location: (3,6)-(3,9))
            ├── flags: variable_call, ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :baz
            ├── message_loc: (3,6)-(3,9) = "baz"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅