@ ProgramNode (location: (0...23))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...23))
    └── body: (length: 1)
        └── @ CallNode (location: (0...23))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...3) = "let"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (4...6))
            │   └── arguments: (length: 1)
            │       └── @ ParenthesesNode (location: (4...6))
            │           ├── body: ∅
            │           ├── opening_loc: (4...5) = "("
            │           └── closing_loc: (5...6) = ")"
            ├── closing_loc: ∅
            ├── block:
            │   @ BlockNode (location: (7...23))
            │   ├── locals: []
            │   ├── parameters: ∅
            │   ├── body:
            │   │   @ StatementsNode (location: (9...21))
            │   │   └── body: (length: 1)
            │   │       └── @ CallNode (location: (9...21))
            │   │           ├── receiver: ∅
            │   │           ├── call_operator_loc: ∅
            │   │           ├── message_loc: (9...10) = "m"
            │   │           ├── opening_loc: (10...11) = "("
            │   │           ├── arguments:
            │   │           │   @ ArgumentsNode (location: (11...12))
            │   │           │   └── arguments: (length: 1)
            │   │           │       └── @ CallNode (location: (11...12))
            │   │           │           ├── receiver: ∅
            │   │           │           ├── call_operator_loc: ∅
            │   │           │           ├── message_loc: (11...12) = "a"
            │   │           │           ├── opening_loc: ∅
            │   │           │           ├── arguments: ∅
            │   │           │           ├── closing_loc: ∅
            │   │           │           ├── block: ∅
            │   │           │           ├── flags: variable_call
            │   │           │           └── name: "a"
            │   │           ├── closing_loc: (12...13) = ")"
            │   │           ├── block:
            │   │           │   @ BlockNode (location: (14...21))
            │   │           │   ├── locals: []
            │   │           │   ├── parameters: ∅
            │   │           │   ├── body: ∅
            │   │           │   ├── opening_loc: (14...16) = "do"
            │   │           │   └── closing_loc: (18...21) = "end"
            │   │           ├── flags: ∅
            │   │           └── name: "m"
            │   ├── opening_loc: (7...8) = "{"
            │   └── closing_loc: (22...23) = "}"
            ├── flags: ∅
            └── name: "let"
