@ ProgramNode (location: (0...7))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...7))
    └── body: (length: 1)
        └── @ CallNode (location: (0...7))
            ├── receiver:
            │   @ CallNode (location: (2...7))
            │   ├── receiver:
            │   │   @ CallNode (location: (2...3))
            │   │   ├── receiver: ∅
            │   │   ├── call_operator_loc: ∅
            │   │   ├── message_loc: (2...3) = "a"
            │   │   ├── opening_loc: ∅
            │   │   ├── arguments: ∅
            │   │   ├── closing_loc: ∅
            │   │   ├── block: ∅
            │   │   ├── flags: variable_call
            │   │   └── name: "a"
            │   ├── call_operator_loc: (3...4) = "."
            │   ├── message_loc: (4...5) = "b"
            │   ├── opening_loc: ∅
            │   ├── arguments:
            │   │   @ ArgumentsNode (location: (6...7))
            │   │   └── arguments: (length: 1)
            │   │       └── @ IntegerNode (location: (6...7))
            │   │           └── flags: decimal
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: ∅
            │   └── name: "b"
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "!"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: ∅
            └── name: "!"
