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