@ ProgramNode (location: (0...13))
├── locals: []
└── statements:
    @ StatementsNode (location: (0...13))
    └── body: (length: 1)
        └── @ UndefNode (location: (0...13))
            ├── names: (length: 1)
            │   └── @ SymbolNode (location: (6...13))
            │       ├── opening_loc: (6...9) = "%s("
            │       ├── value_loc: (9...12) = "foo"
            │       ├── closing_loc: (12...13) = ")"
            │       └── unescaped: "foo"
            └── keyword_loc: (0...5) = "undef"
