@ ProgramNode (location: (0...22))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...22))
    └── body: (length: 1)
        └── @ CallNode (location: (0...22))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...3) = "let"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (4...8))
            │   └── arguments: (length: 1)
            │       └── @ ParenthesesNode (location: (4...8))
            │           ├── body:
            │           │   @ StatementsNode (location: (5...7))
            │           │   └── body: (length: 1)
            │           │       └── @ SymbolNode (location: (5...7))
            │           │           ├── opening_loc: (5...6) = ":"
            │           │           ├── value_loc: (6...7) = "a"
            │           │           ├── closing_loc: ∅
            │           │           └── unescaped: "a"
            │           ├── opening_loc: (4...5) = "("
            │           └── closing_loc: (7...8) = ")"
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (9...22))
            │   ├── locals: []
            │   ├── parameters: ∅
            │   ├── body:
            │   │   @ StatementsNode (location: (11...20))
            │   │   └── body: (length: 1)
            │   │       └── @ CallNode (location: (11...20))
            │   │           ├── receiver: ∅
            │   │           ├── call_operator_loc: ∅
            │   │           ├── message_loc: (11...12) = "m"
            │   │           ├── opening_loc: ∅
            │   │           ├── arguments: ∅
            │   │           ├── closing_loc: ∅
            │   │           ├── block:
            │   │           │   @ BlockNode (location: (13...20))
            │   │           │   ├── locals: []
            │   │           │   ├── parameters: ∅
            │   │           │   ├── body: ∅
            │   │           │   ├── opening_loc: (13...15) = "do"
            │   │           │   └── closing_loc: (17...20) = "end"
            │   │           ├── flags: ∅
            │   │           └── name: "m"
            │   ├── opening_loc: (9...10) = "{"
            │   └── closing_loc: (21...22) = "}"
            ├── flags: ∅
            └── name: "let"
