@ ProgramNode (location: (0...11))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...11))
    └── body: (length: 1)
        └── @ CallNode (location: (0...11))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (0...3) = "foo"
            ├── opening_loc: (3...4) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (4...10))
            │   └── arguments: (length: 1)
            │       └── @ KeywordHashNode (location: (4...10))
            │           └── elements: (length: 2)
            │               ├── @ AssocNode (location: (4...6))
            │               │   ├── key:
            │               │   │   @ SymbolNode (location: (4...6))
            │               │   │   ├── opening_loc: ∅
            │               │   │   ├── value_loc: (4...5) = "a"
            │               │   │   ├── closing_loc: (5...6) = ":"
            │               │   │   └── unescaped: "a"
            │               │   ├── value: ∅
            │               │   └── operator_loc: ∅
            │               └── @ AssocNode (location: (8...10))
            │                   ├── key:
            │                   │   @ SymbolNode (location: (8...10))
            │                   │   ├── opening_loc: ∅
            │                   │   ├── value_loc: (8...9) = "b"
            │                   │   ├── closing_loc: (9...10) = ":"
            │                   │   └── unescaped: "b"
            │                   ├── value: ∅
            │                   └── operator_loc: ∅
            ├── closing_loc: (10...11) = ")"
            ├── block: ∅
            ├── flags: ∅
            └── name: "foo"
