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