@ ProgramNode (location: (0...23))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...23))
    └── body: (length: 1)
        └── @ LambdaNode (location: (0...23))
            ├── locals: [:b, :c, :d, :e, :f]
            ├── operator_loc: (0...2) = "->"
            ├── opening_loc: (21...22) = "{"
            ├── closing_loc: (22...23) = "}"
            ├── parameters:
            │   @ BlockParametersNode (location: (2...21))
            │   ├── parameters:
            │   │   @ ParametersNode (location: (3...20))
            │   │   ├── requireds: (length: 1)
            │   │   │   └── @ RequiredParameterNode (location: (3...4))
            │   │   │       └── name: :b
            │   │   ├── optionals: (length: 1)
            │   │   │   └── @ OptionalParameterNode (location: (6...9))
            │   │   │       ├── name: :c
            │   │   │       ├── name_loc: (6...7) = "c"
            │   │   │       ├── operator_loc: (7...8) = "="
            │   │   │       └── value:
            │   │   │           @ IntegerNode (location: (8...9))
            │   │   │           └── flags: decimal
            │   │   ├── rest:
            │   │   │   @ RestParameterNode (location: (11...13))
            │   │   │   ├── name: :d
            │   │   │   ├── name_loc: (12...13) = "d"
            │   │   │   └── operator_loc: (11...12) = "*"
            │   │   ├── posts: (length: 1)
            │   │   │   └── @ RequiredParameterNode (location: (15...16))
            │   │   │       └── name: :e
            │   │   ├── keywords: (length: 0)
            │   │   ├── keyword_rest: ∅
            │   │   └── block:
            │   │       @ BlockParameterNode (location: (18...20))
            │   │       ├── name: :f
            │   │       ├── name_loc: (19...20) = "f"
            │   │       └── operator_loc: (18...19) = "&"
            │   ├── locals: (length: 0)
            │   ├── opening_loc: (2...3) = "("
            │   └── closing_loc: (20...21) = ")"
            └── body: ∅
