@ ProgramNode (location: (1,0)-(1,17))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,17))
    └── body: (length: 1)
        └── @ DefNode (location: (1,0)-(1,17))
            ├── name: :!
            ├── name_loc: (1,4)-(1,5) = "!"
            ├── receiver: ∅
            ├── parameters: ∅
            ├── body:
            │   @ StatementsNode (location: (1,8)-(1,12))
            │   └── body: (length: 1)
            │       └── @ TrueNode (location: (1,8)-(1,12))
            ├── locals: []
            ├── def_keyword_loc: (1,0)-(1,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: ∅
            ├── rparen_loc: ∅
            ├── equal_loc: ∅
            └── end_keyword_loc: (1,14)-(1,17) = "end"
