@ ProgramNode (location: (1,4)-(3,7))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,4)-(3,7))
    └── body: (length: 1)
        └── @ DefNode (location: (1,4)-(3,7))
            ├── name: :hi
            ├── name_loc: (1,8)-(1,10) = "hi"
            ├── receiver: ∅
            ├── parameters: ∅
            ├── body: ∅
            ├── locals: []
            ├── def_keyword_loc: (1,4)-(1,7) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: ∅
            ├── rparen_loc: ∅
            ├── equal_loc: ∅
            └── end_keyword_loc: (3,4)-(3,7) = "end"