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