@ ProgramNode (location: (0...10))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...10))
    └── body: (length: 1)
        └── @ CallNode (location: (0...10))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "a"
            ├── opening_loc: ∅
            ├── arguments: ∅
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (2...10))
            │   ├── locals: [:b]
            │   ├── parameters:
            │   │   @ BlockParametersNode (location: (4...8))
            │   │   ├── parameters: ∅
            │   │   ├── locals: (length: 1)
            │   │   │   └── @ BlockLocalVariableNode (location: (6...7))
            │   │   │       └── name: :b
            │   │   ├── opening_loc: (4...5) = "|"
            │   │   └── closing_loc: (7...8) = "|"
            │   ├── body: ∅
            │   ├── opening_loc: (2...3) = "{"
            │   └── closing_loc: (9...10) = "}"
            ├── flags: ∅
            └── name: "a"
