@ ProgramNode (location: (1,0)-(1,5))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,5))
    └── body: (length: 1)
        └── @ LambdaNode (location: (1,0)-(1,5))
            ├── locals: [:a]
            ├── operator_loc: (1,0)-(1,2) = "->"
            ├── opening_loc: (1,3)-(1,4) = "{"
            ├── closing_loc: (1,4)-(1,5) = "}"
            ├── parameters:
            │   @ BlockParametersNode (location: (1,2)-(1,3))
            │   ├── parameters:
            │   │   @ ParametersNode (location: (1,2)-(1,3))
            │   │   ├── requireds: (length: 1)
            │   │   │   └── @ RequiredParameterNode (location: (1,2)-(1,3))
            │   │   │       ├── flags: ∅
            │   │   │       └── name: :a
            │   │   ├── optionals: (length: 0)
            │   │   ├── rest: ∅
            │   │   ├── posts: (length: 0)
            │   │   ├── keywords: (length: 0)
            │   │   ├── keyword_rest: ∅
            │   │   └── block: ∅
            │   ├── locals: (length: 0)
            │   ├── opening_loc: ∅
            │   └── closing_loc: ∅
            └── body: ∅