@ ProgramNode (location: (1,0)-(1,29))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,29))
    └── body: (length: 1)
        └── @ DefNode (location: (1,0)-(1,29))
            ├── name: :a
            ├── name_loc: (1,4)-(1,5) = "a"
            ├── receiver: ∅
            ├── parameters:
            │   @ ParametersNode (location: (1,6)-(1,12))
            │   ├── requireds: (length: 1)
            │   │   └── @ RequiredParameterNode (location: (1,6)-(1,7))
            │   │       ├── flags: ∅
            │   │       └── name: :x
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 0)
            │   ├── keyword_rest:
            │   │   @ ForwardingParameterNode (location: (1,9)-(1,12))
            │   └── block: ∅
            ├── body:
            │   @ StatementsNode (location: (1,15)-(1,24))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (1,15)-(1,24))
            │           ├── flags: ignore_visibility
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── name: :b
            │           ├── message_loc: (1,15)-(1,16) = "b"
            │           ├── opening_loc: (1,16)-(1,17) = "("
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (1,17)-(1,23))
            │           │   ├── flags: ∅
            │           │   └── arguments: (length: 2)
            │           │       ├── @ LocalVariableReadNode (location: (1,17)-(1,18))
            │           │       │   ├── name: :x
            │           │       │   └── depth: 0
            │           │       └── @ ForwardingArgumentsNode (location: (1,20)-(1,23))
            │           ├── closing_loc: (1,23)-(1,24) = ")"
            │           └── block: ∅
            ├── locals: [:x]
            ├── def_keyword_loc: (1,0)-(1,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: (1,5)-(1,6) = "("
            ├── rparen_loc: (1,12)-(1,13) = ")"
            ├── equal_loc: ∅
            └── end_keyword_loc: (1,26)-(1,29) = "end"