@ ProgramNode (location: (4,0)-(5,3))
├── locals: []
└── statements:
    @ StatementsNode (location: (4,0)-(5,3))
    └── body: (length: 1)
        └── @ DefNode (location: (4,0)-(5,3))
            ├── name: :blah
            ├── name_loc: (4,9)-(4,13) = "blah"
            ├── receiver:
            │   @ SelfNode (location: (4,4)-(4,8))
            ├── parameters: ∅
            ├── body: ∅
            ├── locals: []
            ├── def_keyword_loc: (4,0)-(4,3) = "def"
            ├── operator_loc: (4,8)-(4,9) = "."
            ├── lparen_loc: ∅
            ├── rparen_loc: ∅
            ├── equal_loc: ∅
            └── end_keyword_loc: (5,0)-(5,3) = "end"