@ ProgramNode (location: (0...14))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...14))
    └── body: (length: 1)
        └── @ UnlessNode (location: (0...14))
            ├── keyword_loc: (4...10) = "unless"
            ├── predicate:
            │   @ CallNode (location: (11...14))
            │   ├── receiver: ∅
            │   ├── call_operator_loc: ∅
            │   ├── message_loc: (11...14) = "foo"
            │   ├── opening_loc: ∅
            │   ├── arguments: ∅
            │   ├── closing_loc: ∅
            │   ├── block: ∅
            │   ├── flags: variable_call
            │   └── name: "foo"
            ├── statements:
            │   @ StatementsNode (location: (0...3))
            │   └── body: (length: 1)
            │       └── @ CallNode (location: (0...3))
            │           ├── receiver: ∅
            │           ├── call_operator_loc: ∅
            │           ├── message_loc: (0...3) = "bar"
            │           ├── opening_loc: ∅
            │           ├── arguments: ∅
            │           ├── closing_loc: ∅
            │           ├── block: ∅
            │           ├── flags: variable_call
            │           └── name: "bar"
            ├── consequent: ∅
            └── end_keyword_loc: ∅
