Applying Constraint Handling Rules to HPSG

Constraint Handling Rules (CHR) have provided a realistic solution to an over-arching problem in many elds that deal with constraint logic programming: how to combine recursive functions or relations with constraints while avoiding non-termination problems. This paper focuses on some other bene ts that CHR, speci cally their implementation in SICStus Prolog, have provided to computational linguists working on grammar design tools. CHR rules are applied by means of a subsumption check and this check is made only when their variables are instantiated or bound. The former functionality is at best di cult to simulate using more primitive coroutining statements such as SICStus when/2, and the latter simply did not exist in any form before CHR. For the sake of providing a case study in how these can be applied to grammar development, we consider the Attribute Logic Engine (ALE), a Prolog preprocessor for logic programming with typed feature structures, and its extension to a complete grammar development system for Head-driven Phrase Structure Grammar (HPSG), a popular constraintbased linguistic theory that uses typed feature structures. In this context, CHR can be used not only to extend the constraint language of feature structure descriptions to include relations in a declarative way, but also to provide support for constraints with complex antecedents and constraints on the co-occurrence of feature values that are necessary to interpret the type system of HPSG properly. Constraint Handling Rules [CHR, Fr uhwirth and Abdennadher, 1997] have provided a realistic solution to an over-arching problem in many elds that deal with constraint logic programming: how to combine recursive functions or relations with constraints while avoiding non-termination problems. Potential applications of constraint logic programming within computational linguistics have certainly not been immune to this problem, and for them, CHR is currently the only existing tractable alternative to manually specifying a set of delay statements to avoid non-termination in a space of constraints with huge numbers of non-deterministic constraints and relational attachments that are almost invariably recursive. This paper focuses on some other bene ts that CHR, speci cally its implementation in SICStus Prolog, has provided to computational linguists working on grammar design tools. CHR rules are applied through a subsumption check and this check is made only when their variables are instantiated or bound. The former functionality is at best di cult to simulate using more primitive coroutining statements such as SICStus when/2, and the latter simply did not exist in any form before CHR, to the best of this author’s knowledge. For the sake of providing a case study in how these can be applied to grammar development, we will consider the Attribute Logic Engine (ALE) [Carpenter and Penn, 1996], a Prolog prepro-