@ ProgramNode (location: (1,0)-(1,20))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,20))
    └── body: (length: 1)
        └── @ DefNode (location: (1,0)-(1,20))
            ├── name: :return
            ├── name_loc: (1,9)-(1,15) = "return"
            ├── receiver:
            │   @ SelfNode (location: (1,4)-(1,8))
            ├── parameters: ∅
            ├── body: ∅
            ├── locals: []
            ├── def_keyword_loc: (1,0)-(1,3) = "def"
            ├── operator_loc: (1,8)-(1,9) = "."
            ├── lparen_loc: ∅
            ├── rparen_loc: ∅
            ├── equal_loc: ∅
            └── end_keyword_loc: (1,17)-(1,20) = "end"