@ ProgramNode (location: (0...17))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...17))
    └── body: (length: 1)
        └── @ CallNode (location: (0...17))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "f"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (2...17))
            │   ├── locals: [:a, :b]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (4...15))
            │   │   ├── parameters:
            │   │   │   @ ParametersNode (location: (5...14))
            │   │   │   ├── requireds: (length: 0)
            │   │   │   ├── optionals: (length: 1)
            │   │   │   │   └── @ OptionalParameterNode (location: (5...11))
            │   │   │   │       ├── name: :a
            │   │   │   │       ├── name_loc: (5...6) = "a"
            │   │   │   │       ├── operator_loc: (7...8) = "="
            │   │   │   │       └── value:
            │   │   │   │           @ IntegerNode (location: (9...11))
            │   │   │   │           └── flags: decimal
            │   │   │   ├── rest: ∅
            │   │   │   ├── posts: (length: 1)
            │   │   │   │   └── @ RequiredParameterNode (location: (13...14))
            │   │   │   │       └── name: :b
            │   │   │   ├── keywords: (length: 0)
            │   │   │   ├── keyword_rest: ∅
            │   │   │   └── block: ∅
            │   │   ├── locals: (length: 0)
            │   │   ├── opening_loc: (4...5) = "|"
            │   │   └── closing_loc: (14...15) = "|"
            │   ├── body: ∅
            │   ├── opening_loc: (2...3) = "{"
            │   └── closing_loc: (16...17) = "}"
            ├── flags: ∅
            └── name: "f"
