@ ProgramNode (location: (1,0)-(1,11))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,11))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,11))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (1,0)-(1,1) = "f"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (1,2)-(1,11))
            │   ├── locals: [:a, :b]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (1,4)-(1,9))
            │   │   ├── parameters:
            │   │   │   @ ParametersNode (location: (1,5)-(1,8))
            │   │   │   ├── requireds: (length: 2)
            │   │   │   │   ├── @ RequiredParameterNode (location: (1,5)-(1,6))
            │   │   │   │   │   └── name: :a
            │   │   │   │   └── @ RequiredParameterNode (location: (1,7)-(1,8))
            │   │   │   │       └── name: :b
            │   │   │   ├── optionals: (length: 0)
            │   │   │   ├── rest: ∅
            │   │   │   ├── posts: (length: 0)
            │   │   │   ├── keywords: (length: 0)
            │   │   │   ├── keyword_rest: ∅
            │   │   │   └── block: ∅
            │   │   ├── locals: (length: 0)
            │   │   ├── opening_loc: (1,4)-(1,5) = "|"
            │   │   └── closing_loc: (1,8)-(1,9) = "|"
            │   ├── body: ∅
            │   ├── opening_loc: (1,2)-(1,3) = "{"
            │   └── closing_loc: (1,10)-(1,11) = "}"
            ├── flags: ∅
            └── name: "f"