@ ProgramNode (location: (1,0)-(1,45))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,45))
    └── body: (length: 1)
        └── @ DefNode (location: (1,0)-(1,45))
            ├── name: :foo
            ├── name_loc: (1,4)-(1,7) = "foo"
            ├── receiver: ∅
            ├── parameters:
            │   @ ParametersNode (location: (1,8)-(1,20))
            │   ├── requireds: (length: 1)
            │   │   └── @ RequiredParameterNode (location: (1,8)-(1,16))
            │   │       ├── flags: ∅
            │   │       └── name: :argument
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 0)
            │   ├── keyword_rest:
            │   │   @ KeywordRestParameterNode (location: (1,18)-(1,20))
            │   │   ├── flags: ∅
            │   │   ├── name: ∅
            │   │   ├── name_loc: ∅
            │   │   └── operator_loc: (1,18)-(1,20) = "**"
            │   └── block: ∅
            ├── body:
            │   @ StatementsNode (location: (1,23)-(1,40))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (1,23)-(1,40))
            │           ├── flags: ignore_visibility
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── name: :bar
            │           ├── message_loc: (1,23)-(1,26) = "bar"
            │           ├── opening_loc: (1,26)-(1,27) = "("
            │           ├── arguments:
            │           │   @ ArgumentsNode (location: (1,27)-(1,39))
            │           │   ├── flags: contains_keywords, contains_keyword_splat
            │           │   └── arguments: (length: 2)
            │           │       ├── @ LocalVariableReadNode (location: (1,27)-(1,35))
            │           │       │   ├── name: :argument
            │           │       │   └── depth: 0
            │           │       └── @ KeywordHashNode (location: (1,37)-(1,39))
            │           │           ├── flags: ∅
            │           │           └── elements: (length: 1)
            │           │               └── @ AssocSplatNode (location: (1,37)-(1,39))
            │           │                   ├── value: ∅
            │           │                   └── operator_loc: (1,37)-(1,39) = "**"
            │           ├── closing_loc: (1,39)-(1,40) = ")"
            │           └── block: ∅
            ├── locals: [:argument]
            ├── def_keyword_loc: (1,0)-(1,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: (1,7)-(1,8) = "("
            ├── rparen_loc: (1,20)-(1,21) = ")"
            ├── equal_loc: ∅
            └── end_keyword_loc: (1,42)-(1,45) = "end"