@ ProgramNode (location: (1,0)-(5,5))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(5,5))
    ├── flags: ∅
    └── body: (length: 2)
        ├── @ DefNode (location: (1,0)-(2,5))
        │   ├── flags: newline
        │   ├── name: :f
        │   ├── name_loc: (1,4)-(1,5) = "f"
        │   ├── receiver: ∅
        │   ├── parameters:
        │   │   @ ParametersNode (location: (1,6)-(1,10))
        │   │   ├── flags: ∅
        │   │   ├── requireds: (length: 0)
        │   │   ├── optionals: (length: 0)
        │   │   ├── rest: ∅
        │   │   ├── posts: (length: 0)
        │   │   ├── keywords: (length: 1)
        │   │   │   └── @ RequiredKeywordParameterNode (location: (1,6)-(1,10))
        │   │   │       ├── flags: ∅
        │   │   │       ├── name: :foo
        │   │   │       └── name_loc: (1,6)-(1,10) = "foo:"
        │   │   ├── keyword_rest: ∅
        │   │   └── block: ∅
        │   ├── body: ∅
        │   ├── locals: [:foo]
        │   ├── def_keyword_loc: (1,0)-(1,3) = "def"
        │   ├── operator_loc: ∅
        │   ├── lparen_loc: ∅
        │   ├── rparen_loc: ∅
        │   ├── equal_loc: ∅
        │   └── end_keyword_loc: (2,2)-(2,5) = "end"
        └── @ DefNode (location: (4,0)-(5,5))
            ├── flags: newline
            ├── name: :f
            ├── name_loc: (4,4)-(4,5) = "f"
            ├── receiver: ∅
            ├── parameters:
            │   @ ParametersNode (location: (4,6)-(4,13))
            │   ├── flags: ∅
            │   ├── requireds: (length: 0)
            │   ├── optionals: (length: 0)
            │   ├── rest: ∅
            │   ├── posts: (length: 0)
            │   ├── keywords: (length: 1)
            │   │   └── @ OptionalKeywordParameterNode (location: (4,6)-(4,13))
            │   │       ├── flags: ∅
            │   │       ├── name: :foo
            │   │       ├── name_loc: (4,6)-(4,10) = "foo:"
            │   │       └── value:
            │   │           @ IntegerNode (location: (4,11)-(4,13))
            │   │           ├── flags: static_literal, decimal
            │   │           └── value: -1
            │   ├── keyword_rest: ∅
            │   └── block: ∅
            ├── body: ∅
            ├── locals: [:foo]
            ├── def_keyword_loc: (4,0)-(4,3) = "def"
            ├── operator_loc: ∅
            ├── lparen_loc: ∅
            ├── rparen_loc: ∅
            ├── equal_loc: ∅
            └── end_keyword_loc: (5,2)-(5,5) = "end"
