@ ProgramNode (location: (1,0)-(1,14))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,14))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,14))
            ├── flags: newline, ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :a
            ├── message_loc: (1,0)-(1,1) = "a"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            └── block:
                @ BlockNode (location: (1,2)-(1,14))
                ├── flags: ∅
                ├── locals: [:b, :c, :d]
                ├── parameters:
                │   @ BlockParametersNode (location: (1,3)-(1,12))
                │   ├── flags: ∅
                │   ├── parameters:
                │   │   @ ParametersNode (location: (1,4)-(1,5))
                │   │   ├── flags: ∅
                │   │   ├── requireds: (length: 1)
                │   │   │   └── @ RequiredParameterNode (location: (1,4)-(1,5))
                │   │   │       ├── flags: ∅
                │   │   │       └── name: :b
                │   │   ├── optionals: (length: 0)
                │   │   ├── rest: ∅
                │   │   ├── posts: (length: 0)
                │   │   ├── keywords: (length: 0)
                │   │   ├── keyword_rest: ∅
                │   │   └── block: ∅
                │   ├── locals: (length: 2)
                │   │   ├── @ BlockLocalVariableNode (location: (1,7)-(1,8))
                │   │   │   ├── flags: ∅
                │   │   │   └── name: :c
                │   │   └── @ BlockLocalVariableNode (location: (1,10)-(1,11))
                │   │       ├── flags: ∅
                │   │       └── name: :d
                │   ├── opening_loc: (1,3)-(1,4) = "|"
                │   └── closing_loc: (1,11)-(1,12) = "|"
                ├── body: ∅
                ├── opening_loc: (1,2)-(1,3) = "{"
                └── closing_loc: (1,13)-(1,14) = "}"
