@ ProgramNode (location: (0...9))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...9))
    └── body: (length: 2)
        ├── @ CallNode (location: (0...7))
        │   ├── receiver: ∅
        │   ├── call_operator_loc: ∅
        │   ├── message_loc: (0...1) = "a"
        │   ├── opening_loc: ∅
        │   ├── arguments:
        │   │   @ ArgumentsNode (location: (2...7))
        │   │   └── arguments: (length: 1)
        │   │       └── @ StringNode (location: (2...7))
        │   │           ├── opening_loc: (2...3) = "\""
        │   │           ├── content_loc: (3...6) = "\\\\n"
        │   │           ├── closing_loc: (6...7) = "\""
        │   │           └── unescaped: "\\n"
        │   ├── closing_loc: ∅
        │   ├── block: ∅
        │   ├── flags: ∅
        │   └── name: "a"
        └── @ CallNode (location: (8...9))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (8...9) = "b"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: variable_call
            └── name: "b"
