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