@ ProgramNode (location: (1,0)-(1,11))
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,11))
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,11))
            ├── receiver: ∅
            ├── call_operator_loc: ∅
            ├── message_loc: (1,0)-(1,1) = "f"
            ├── opening_loc: (1,1)-(1,2) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (1,2)-(1,9))
            │   ├── arguments: (length: 2)
            │   │   ├── @ IntegerNode (location: (1,2)-(1,3))
            │   │   │   └── flags: decimal
            │   │   └── @ KeywordHashNode (location: (1,5)-(1,9))
            │   │       └── elements: (length: 1)
            │   │           └── @ AssocNode (location: (1,5)-(1,9))
            │   │               ├── key:
            │   │               │   @ IntegerNode (location: (1,5)-(1,6))
            │   │               │   └── flags: decimal
            │   │               ├── value:
            │   │               │   @ IntegerNode (location: (1,8)-(1,9))
            │   │               │   └── flags: decimal
            │   │               └── operator_loc: (1,6)-(1,8) = "=>"
            │   └── flags: ∅
            ├── closing_loc: (1,10)-(1,11) = ")"
            ├── block: ∅
            ├── flags: ∅
            └── name: :f
