@ ProgramNode (location: (0...42))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...42))
    └── body: (length: 3)
        ├── @ DefinedNode (location: (0...13))
        │   ├── lparen_loc: ∅
        │   ├── value:
        │   │   @ InstanceVariableReadNode (location: (9...13))
        │   │   └── name: :@foo
        │   ├── rparen_loc: ∅
        │   └── keyword_loc: (0...8) = "defined?"
        ├── @ DefinedNode (location: (15...27))
        │   ├── lparen_loc: ∅
        │   ├── value:
        │   │   @ CallNode (location: (24...27))
        │   │   ├── receiver: ∅
        │   │   ├── call_operator_loc: ∅
        │   │   ├── message_loc: (24...27) = "foo"
        │   │   ├── opening_loc: ∅
        │   │   ├── arguments: ∅
        │   │   ├── closing_loc: ∅
        │   │   ├── block: ∅
        │   │   ├── flags: variable_call
        │   │   └── name: "foo"
        │   ├── rparen_loc: ∅
        │   └── keyword_loc: (15...23) = "defined?"
        └── @ DefinedNode (location: (29...42))
            ├── lparen_loc: (37...38) = "("
            ├── value:
            │   @ CallNode (location: (38...41))
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (38...41) = "foo"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: variable_call
            │   └── name: "foo"
            ├── rparen_loc: (41...42) = ")"
            └── keyword_loc: (29...37) = "defined?"
