@ ProgramNode (location: (0...22))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...22))
    └── body: (length: 1)
        └── @ CallNode (location: (0...22))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...1) = "a"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (2...13))
            │   └── arguments: (length: 1)
            │       └── @ LambdaNode (location: (2...13))
            │           ├── locals: []
            │           ├── operator_loc: (2...4) = "->"
            │           ├── opening_loc: (5...7) = "do"
            │           ├── closing_loc: (10...13) = "end"
            │           ├── parameters: ∅
            │           └── body:
            │               @ StatementsNode (location: (8...9))
            │               └── body: (length: 1)
            │                   └── @ IntegerNode (location: (8...9))
            │                       └── flags: decimal
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (14...22))
            │   ├── locals: []
            │   ├── parameters: ∅
            │   ├── body:
            │   │   @ StatementsNode (location: (17...18))
            │   │   └── body: (length: 1)
            │   │       └── @ IntegerNode (location: (17...18))
            │   │           └── flags: decimal
            │   ├── opening_loc: (14...16) = "do"
            │   └── closing_loc: (19...22) = "end"
            ├── flags: ∅
            └── name: "a"
