A Classification of Noncircular Attribute Grammars Based on the Look-Ahead Behavior

  • Authors:
  • Wuu Yang

  • Affiliations:
  • National Chiao-Tung Univ., HsinChu, Taiwan

  • Venue:
  • IEEE Transactions on Software Engineering
  • Year:
  • 2002

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Abstract

We propose a family of static evaluators for subclasses of the well-defined (i.e., noncircular) attribute grammars. These evaluators augment the evaluator for the absolutely noncircular attribute grammars with look-ahead behaviors. Because this family covers exactly the set of all well-defined attribute grammars, well-defined attribute grammars may be classified into a hierarchy, called the $NC$ hierarchy, according to their evaluators in the family. The location of a noncircular attribute grammar in the $NC$ hierarchy is an intrinsic property of the grammar. The $NC$ hierarchy confirms a result of Riis and Skyum, which says that all well-defined attribute grammars allow a (static) pure multivisit evaluator by actually constructing such an evaluator. We also show that, for any finite $m$, an $NC(m)$ attribute grammar can be transformed to an equivalent $NC(0)$ grammar.