@ ProgramNode (location: (0...15))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...15))
    └── body: (length: 2)
        ├── @ CallNode (location: (0...7))
        │   ├── receiver: ∅
        │   ├── call_operator_loc: ∅
        │   ├── message_loc: (0...1) = "x"
        │   ├── opening_loc: ∅
        │   ├── arguments: ∅
        │   ├── closing_loc: ∅
        │   ├── block:
        │   │   @ BlockNode (location: (1...7))
        │   │   ├── locals: [:a]
        │   │   ├── parameters:
        │   │   │   @ BlockParametersNode (location: (2...6))
        │   │   │   ├── parameters:
        │   │   │   │   @ ParametersNode (location: (3...5))
        │   │   │   │   ├── requireds: (length: 1)
        │   │   │   │   │   └── @ RequiredParameterNode (location: (3...4))
        │   │   │   │   │       └── name: :a
        │   │   │   │   ├── optionals: (length: 0)
        │   │   │   │   ├── rest:
        │   │   │   │   │   @ RestParameterNode (location: (4...5))
        │   │   │   │   │   ├── name: nil
        │   │   │   │   │   ├── name_loc: ∅
        │   │   │   │   │   └── operator_loc: (4...5) = ","
        │   │   │   │   ├── posts: (length: 0)
        │   │   │   │   ├── keywords: (length: 0)
        │   │   │   │   ├── keyword_rest: ∅
        │   │   │   │   └── block: ∅
        │   │   │   ├── locals: (length: 0)
        │   │   │   ├── opening_loc: (2...3) = "|"
        │   │   │   └── closing_loc: (5...6) = "|"
        │   │   ├── body: ∅
        │   │   ├── opening_loc: (1...2) = "{"
        │   │   └── closing_loc: (6...7) = "}"
        │   ├── flags: ∅
        │   └── name: "x"
        └── @ CallNode (location: (9...15))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (9...10) = "x"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (10...15))
            │   ├── locals: [:a]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (11...14))
            │   │   ├── parameters:
            │   │   │   @ ParametersNode (location: (12...13))
            │   │   │   ├── requireds: (length: 1)
            │   │   │   │   └── @ RequiredParameterNode (location: (12...13))
            │   │   │   │       └── name: :a
            │   │   │   ├── optionals: (length: 0)
            │   │   │   ├── rest: ∅
            │   │   │   ├── posts: (length: 0)
            │   │   │   ├── keywords: (length: 0)
            │   │   │   ├── keyword_rest: ∅
            │   │   │   └── block: ∅
            │   │   ├── locals: (length: 0)
            │   │   ├── opening_loc: (11...12) = "|"
            │   │   └── closing_loc: (13...14) = "|"
            │   ├── body: ∅
            │   ├── opening_loc: (10...11) = "{"
            │   └── closing_loc: (14...15) = "}"
            ├── flags: ∅
            └── name: "x"
