@ ProgramNode (location: (1,0)-(1,9))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,9))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,9))
            ├── flags: newline
            ├── receiver:
            │   @ CallNode (location: (1,4)-(1,9))
            │   ├── flags: ignore_visibility
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :m
            │   ├── message_loc: (1,4)-(1,5) = "m"
            │   ├── opening_loc: ∅
            │   ├── arguments:
            │   │   @ ArgumentsNode (location: (1,6)-(1,9))
            │   │   ├── flags: ∅
            │   │   └── arguments: (length: 1)
            │   │       └── @ CallNode (location: (1,6)-(1,9))
            │   │           ├── flags: variable_call, ignore_visibility
            │   │           ├── receiver: ∅
            │   │           ├── call_operator_loc: ∅
            │   │           ├── name: :foo
            │   │           ├── message_loc: (1,6)-(1,9) = "foo"
            │   │           ├── opening_loc: ∅
            │   │           ├── arguments: ∅
            │   │           ├── closing_loc: ∅
            │   │           └── block: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: ∅
            ├── name: :!
            ├── message_loc: (1,0)-(1,3) = "not"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block: ∅
