@ ProgramNode (location: (1,0)-(1,9))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,9))
    └── body: (length: 1)
        └── @ CallOperatorWriteNode (location: (1,0)-(1,9))
            ├── flags: ∅
            ├── receiver:
            │   @ ConstantReadNode (location: (1,0)-(1,1))
            │   └── name: :A
            ├── call_operator_loc: (1,1)-(1,3) = "::"
            ├── message_loc: (1,3)-(1,4) = "b"
            ├── read_name: :b
            ├── write_name: :b=
            ├── operator: :+
            ├── operator_loc: (1,5)-(1,7) = "+="
            └── value:
                @ IntegerNode (location: (1,8)-(1,9))
                ├── flags: decimal
                └── value: 1