@ ProgramNode (location: (1,0)-(1,10))
├── flags: ∅
├── locals: []
└── statements:
    @ StatementsNode (location: (1,0)-(1,10))
    ├── flags: ∅
    └── body: (length: 1)
        └── @ CallNode (location: (1,0)-(1,10))
            ├── flags: newline
            ├── receiver:
            │   @ CallNode (location: (1,0)-(1,1))
            │   ├── flags: variable_call, ignore_visibility
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── name: :a
            │   ├── message_loc: (1,0)-(1,1) = "a"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   └── block: ∅
            ├── call_operator_loc: (1,1)-(1,2) = "."
            ├── name: :f
            ├── message_loc: (1,2)-(1,3) = "f"
            ├── opening_loc: (1,3)-(1,4) = "("
            ├── arguments:
            │   @ ArgumentsNode (location: (1,4)-(1,8))
            │   ├── flags: contains_keywords
            │   └── arguments: (length: 1)
            │       └── @ KeywordHashNode (location: (1,4)-(1,8))
            │           ├── flags: ∅
            │           └── elements: (length: 1)
            │               └── @ AssocNode (location: (1,4)-(1,8))
            │                   ├── flags: static_literal
            │                   ├── key:
            │                   │   @ IntegerNode (location: (1,4)-(1,5))
            │                   │   ├── flags: static_literal, decimal
            │                   │   └── value: 1
            │                   ├── value:
            │                   │   @ IntegerNode (location: (1,7)-(1,8))
            │                   │   ├── flags: static_literal, decimal
            │                   │   └── value: 2
            │                   └── operator_loc: (1,5)-(1,7) = "=>"
            ├── closing_loc: (1,9)-(1,10) = ")"
            └── block: ∅
