@ ProgramNode (location: (1,0)-(1,19))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,19))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,19))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (1,0)-(1,1) = "a"
            ├── opening_loc: ∅
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(1,19))
            │   ├── arguments: (length: 1)
            │   │   └── @ ArrayNode (location: (1,2)-(1,19))
            │   │       ├── elements: (length: 2)
            │   │       │   ├── @ NilNode (location: (1,4)-(1,7))
            │   │       │   └── @ CallNode (location: (1,9)-(1,17))
            │   │       │       ├── receiver: ∅
            │   │       │       ├── call_operator_loc: ∅
            │   │       │       ├── message_loc: (1,9)-(1,10) = "b"
            │   │       │       ├── opening_loc: ∅
            │   │       │       ├── arguments: ∅
            │   │       │       ├── closing_loc: ∅
            │   │       │       ├── block:
            │   │       │       │   @ BlockNode (location: (1,11)-(1,17))
            │   │       │       │   ├── locals: []
            │   │       │       │   ├── parameters: ∅
            │   │       │       │   ├── body: ∅
            │   │       │       │   ├── opening_loc: (1,11)-(1,13) = "do"
            │   │       │       │   └── closing_loc: (1,14)-(1,17) = "end"
            │   │       │       ├── flags: ∅
            │   │       │       └── name: :b
            │   │       ├── opening_loc: (1,2)-(1,3) = "["
            │   │       └── closing_loc: (1,18)-(1,19) = "]"
            │   └── flags: ∅
            ├── closing_loc: ∅
            ├── block: ∅
            ├── flags: ∅
            └── name: :a
