@ ProgramNode (location: (0...19))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...19))
    └── body: (length: 1)
        └── @ LambdaNode (location: (0...19))
            ├── locals: [:a, :foo, :bar]
            ├── operator_loc: (0...2) = "->"
            ├── opening_loc: (16...17) = "{"
            ├── closing_loc: (18...19) = "}"
            ├── parameters:
            │   @ BlockParametersNode (location: (2...15))
            │   ├── parameters:
            │   │   @ ParametersNode (location: (3...4))
            │   │   ├── requireds: (length: 1)
            │   │   │   └── @ RequiredParameterNode (location: (3...4))
            │   │   │       └── name: :a
            │   │   ├── optionals: (length: 0)
            │   │   ├── rest: ∅
            │   │   ├── posts: (length: 0)
            │   │   ├── keywords: (length: 0)
            │   │   ├── keyword_rest: ∅
            │   │   └── block: ∅
            │   ├── locals: (length: 2)
            │   │   ├── @ BlockLocalVariableNode (location: (6...9))
            │   │   │   └── name: :foo
            │   │   └── @ BlockLocalVariableNode (location: (11...14))
            │   │       └── name: :bar
            │   ├── opening_loc: (2...3) = "("
            │   └── closing_loc: (14...15) = ")"
            └── body: ∅
