@ ProgramNode (location: (1,0)-(1,6))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,6))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,6))
            ├── flags: ignore_visibility
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── name: :a
            ├── message_loc: (1,0)-(1,1) = "a"
            ├── opening_loc: (1,1)-(1,2) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(1,5))
            │   ├── flags: contains_keyword_splat
            │   └── arguments: (length: 1)
            │       └── @ KeywordHashNode (location: (1,2)-(1,5))
            │           ├── flags: ∅
            │           └── elements: (length: 1)
            │               └── @ AssocSplatNode (location: (1,2)-(1,5))
            │                   ├── value:
            │                   │   @ IntegerNode (location: (1,4)-(1,5))
            │                   │   ├── flags: decimal
            │                   │   └── value: 1
            │                   └── operator_loc: (1,2)-(1,4) = "**"
            ├── closing_loc: (1,5)-(1,6) = ")"
            └── block: ∅