@ ProgramNode (location: (0...25))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...25))
    └── body: (length: 1)
        └── @ CallNode (location: (0...25))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "f"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (2...25))
            │   ├── locals: [:a, :b, :c, :d]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (4...23))
            │   │   ├── parameters:
            │   │   │   @ ParametersNode (location: (5...22))
            │   │   │   ├── requireds: (length: 1)
            │   │   │   │   └── @ RequiredParameterNode (location: (5...6))
            │   │   │   │       └── name: :a
            │   │   │   ├── optionals: (length: 1)
            │   │   │   │   └── @ OptionalParameterNode (location: (8...14))
            │   │   │   │       ├── name: :b
            │   │   │   │       ├── name_loc: (8...9) = "b"
            │   │   │   │       ├── operator_loc: (10...11) = "="
            │   │   │   │       └── value:
            │   │   │   │           @ IntegerNode (location: (12...14))
            │   │   │   │           └── flags: decimal
            │   │   │   ├── rest:
            │   │   │   │   @ RestParameterNode (location: (16...18))
            │   │   │   │   ├── name: :c
            │   │   │   │   ├── name_loc: (17...18) = "c"
            │   │   │   │   └── operator_loc: (16...17) = "*"
            │   │   │   ├── posts: (length: 0)
            │   │   │   ├── keywords: (length: 0)
            │   │   │   ├── keyword_rest: ∅
            │   │   │   └── block:
            │   │   │       @ BlockParameterNode (location: (20...22))
            │   │   │       ├── name: :d
            │   │   │       ├── name_loc: (21...22) = "d"
            │   │   │       └── operator_loc: (20...21) = "&"
            │   │   ├── locals: (length: 0)
            │   │   ├── opening_loc: (4...5) = "|"
            │   │   └── closing_loc: (22...23) = "|"
            │   ├── body: ∅
            │   ├── opening_loc: (2...3) = "{"
            │   └── closing_loc: (24...25) = "}"
            ├── flags: ∅
            └── name: "f"
