@ ProgramNode (location: (1,0)-(1,15))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,15))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,15))
            ├── flags: ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :a
            ├── message_loc: (1,0)-(1,1) = "a"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(1,4))
            │   ├── flags: ∅
            │   └── arguments: (length: 1)
            │       └── @ InstanceVariableReadNode (location: (1,2)-(1,4))
            │           └── name: :@b
            ├── closing_loc: ∅
            └── block:
                @ BlockNode (location: (1,5)-(1,15))
                ├── locals: [:c]
                ├── parameters:
                │   @ BlockParametersNode (location: (1,8)-(1,11))
                │   ├── parameters:
                │   │   @ ParametersNode (location: (1,9)-(1,10))
                │   │   ├── requireds: (length: 1)
                │   │   │   └── @ RequiredParameterNode (location: (1,9)-(1,10))
                │   │   │       ├── flags: ∅
                │   │   │       └── name: :c
                │   │   ├── optionals: (length: 0)
                │   │   ├── rest: ∅
                │   │   ├── posts: (length: 0)
                │   │   ├── keywords: (length: 0)
                │   │   ├── keyword_rest: ∅
                │   │   └── block: ∅
                │   ├── locals: (length: 0)
                │   ├── opening_loc: (1,8)-(1,9) = "|"
                │   └── closing_loc: (1,10)-(1,11) = "|"
                ├── body: ∅
                ├── opening_loc: (1,5)-(1,7) = "do"
                └── closing_loc: (1,12)-(1,15) = "end"