@ ProgramNode (location: (0...30))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...30))
    └── body: (length: 1)
        └── @ UntilNode (location: (0...30))
            ├── keyword_loc: (0...5) = "until"
            ├── closing_loc: (27...30) = "end"
            ├── predicate:
            │   @ CallNode (location: (6...18))
            │   ├── receiver:
            │   │   @ CallNode (location: (10...18))
            │   │   ├── receiver:
            │   │   │   @ CallNode (location: (10...13))
            │   │   │   ├── receiver: ∅
            │   │   │   ├── call_operator_loc: ∅
            │   │   │   ├── message_loc: (10...13) = "var"
            │   │   │   ├── opening_loc: ∅
            │   │   │   ├── arguments: ∅
            │   │   │   ├── closing_loc: ∅
            │   │   │   ├── block: ∅
            │   │   │   ├── flags: variable_call
            │   │   │   └── name: "var"
            │   │   ├── call_operator_loc: (13...14) = "."
            │   │   ├── message_loc: (14...18) = "nil?"
            │   │   ├── opening_loc: ∅
            │   │   ├── arguments: ∅
            │   │   ├── closing_loc: ∅
            │   │   ├── block: ∅
            │   │   ├── flags: ∅
            │   │   └── name: "nil?"
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (6...9) = "not"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: ∅
            │   └── name: "!"
            ├── statements:
            │   @ StatementsNode (location: (21...26))
            │   └── body: (length: 1)
            │       └── @ StringNode (location: (21...26))
            │           ├── opening_loc: (21...22) = "'"
            │           ├── content_loc: (22...25) = "foo"
            │           ├── closing_loc: (25...26) = "'"
            │           └── unescaped: "foo"
            └── flags: ∅
