@ ProgramNode (location: (0...13))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...13))
    └── body: (length: 1)
        └── @ CallNode (location: (0...13))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...6) = "lambda"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (6...13))
            │   ├── locals: [:a]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (7...11))
            │   │   ├── parameters: ∅
            │   │   ├── locals: (length: 1)
            │   │   │   └── @ BlockLocalVariableNode (location: (9...10))
            │   │   │       └── name: :a
            │   │   ├── opening_loc: (7...8) = "|"
            │   │   └── closing_loc: (10...11) = "|"
            │   ├── body:
            │   │   @ StatementsNode (location: (11...12))
            │   │   └── body: (length: 1)
            │   │       └── @ LocalVariableReadNode (location: (11...12))
            │   │           ├── name: :a
            │   │           └── depth: 0
            │   ├── opening_loc: (6...7) = "{"
            │   └── closing_loc: (12...13) = "}"
            ├── flags: ∅
            └── name: "lambda"
