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