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