@ ProgramNode (location: (0...12))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...12))
    └── body: (length: 1)
        └── @ DefinedNode (location: (0...12))
            ├── lparen_loc: (8...9) = "("
            ├── value:
            │   @ IntegerNode (location: (9...11))
            │   └── flags: decimal
            ├── rparen_loc: (11...12) = ")"
            └── keyword_loc: (0...8) = "defined?"
