@ ProgramNode (location: (1,0)-(1,6))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,6))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,6))
            ├── flags: ∅
            ├── receiver:
            │   @ CallNode (location: (1,4)-(1,5))
            │   ├── flags: variable_call
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :a
            │   ├── message_loc: (1,4)-(1,5) = "a"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: ∅
            ├── name: :!
            ├── message_loc: (1,0)-(1,3) = "not"
            ├── opening_loc: (1,3)-(1,4) = "("
            ├── arguments: ∅
            ├── closing_loc: (1,5)-(1,6) = ")"
            └── block: ∅
