From Attribute Grammars to Constraint Handling Rules

Attribute grammars provide a framework to define computations over trees, by decorating those trees with attributes. Attribute grammars have been successfully applied in many areas, including compiler construction and natural language processing. In this paper we present a translation of attribute grammars to Constraint Handling Rules, a formalism based on constraint rewriting. Our translation is able to express in a simple way several extensions to attribute grammars. Higher-order attributes are attributes whose value is again a tree, for which attributes can be computed recursively. Lookahead enables attribute definitions to depend not only on the current node, but also on the shape of its subtrees. Specialization provides a way to override the default computation of an attribute when some conditions are met; a natural way to define exceptions to the default tree processing.