@ ProgramNode (location: (1,0)-(3,9))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(3,9))
    └── body: (length: 2)
        ├── @ LambdaNode (location: (1,0)-(1,11))
        │   ├── locals: [:a]
        │   ├── operator_loc: (1,0)-(1,2) = "->"
        │   ├── opening_loc: (1,8)-(1,9) = "{"
        │   ├── closing_loc: (1,10)-(1,11) = "}"
        │   ├── parameters:
        │   │   @ BlockParametersNode (location: (1,3)-(1,7))
        │   │   ├── parameters:
        │   │   │   @ ParametersNode (location: (1,3)-(1,7))
        │   │   │   ├── requireds: (length: 0)
        │   │   │   ├── optionals: (length: 0)
        │   │   │   ├── rest: ∅
        │   │   │   ├── posts: (length: 0)
        │   │   │   ├── keywords: (length: 1)
        │   │   │   │   └── @ OptionalKeywordParameterNode (location: (1,3)-(1,7))
        │   │   │   │       ├── flags: ∅
        │   │   │   │       ├── name: :a
        │   │   │   │       ├── name_loc: (1,3)-(1,5) = "a:"
        │   │   │   │       └── value:
        │   │   │   │           @ IntegerNode (location: (1,6)-(1,7))
        │   │   │   │           └── flags: decimal
        │   │   │   ├── keyword_rest: ∅
        │   │   │   └── block: ∅
        │   │   ├── locals: (length: 0)
        │   │   ├── opening_loc: ∅
        │   │   └── closing_loc: ∅
        │   └── body: ∅
        └── @ LambdaNode (location: (3,0)-(3,9))
            ├── locals: [:a]
            ├── operator_loc: (3,0)-(3,2) = "->"
            ├── opening_loc: (3,6)-(3,7) = "{"
            ├── closing_loc: (3,8)-(3,9) = "}"
            ├── parameters:
            │   @ BlockParametersNode (location: (3,3)-(3,5))
            │   ├── parameters:
            │   │   @ ParametersNode (location: (3,3)-(3,5))
            │   │   ├── requireds: (length: 0)
            │   │   ├── optionals: (length: 0)
            │   │   ├── rest: ∅
            │   │   ├── posts: (length: 0)
            │   │   ├── keywords: (length: 1)
            │   │   │   └── @ RequiredKeywordParameterNode (location: (3,3)-(3,5))
            │   │   │       ├── flags: ∅
            │   │   │       ├── name: :a
            │   │   │       └── name_loc: (3,3)-(3,5) = "a:"
            │   │   ├── keyword_rest: ∅
            │   │   └── block: ∅
            │   ├── locals: (length: 0)
            │   ├── opening_loc: ∅
            │   └── closing_loc: ∅
            └── body: ∅
