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