@ ProgramNode (location: (0...19))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...19))
    └── body: (length: 1)
        └── @ CallNode (location: (0...19))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "a"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (2...10))
            │   └── arguments: (length: 1)
            │       └── @ LambdaNode (location: (2...10))
            │           ├── locals: []
            │           ├── operator_loc: (2...4) = "->"
            │           ├── opening_loc: (5...6) = "{"
            │           ├── closing_loc: (9...10) = "}"
            │           ├── parameters: ∅
            │           └── body:
            │               @ StatementsNode (location: (7...8))
            │               └── body: (length: 1)
            │                   └── @ IntegerNode (location: (7...8))
            │                       └── flags: decimal
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (11...19))
            │   ├── locals: []
            │   ├── parameters: ∅
            │   ├── body:
            │   │   @ StatementsNode (location: (14...15))
            │   │   └── body: (length: 1)
            │   │       └── @ IntegerNode (location: (14...15))
            │   │           └── flags: decimal
            │   ├── opening_loc: (11...13) = "do"
            │   └── closing_loc: (16...19) = "end"
            ├── flags: ∅
            └── name: "a"
