We illustrated that recursive lexical constraints might be useful from a linguistic perspective. If lexical rules are formalized as complex constraints on lexical categories then methods from logic programming can be used to implement such constraints.
Note that complex constraints and delayed evaluation techniques are also useful in other areas of linguistic desciption. For example we used the same methods to define and process HPSG's FOOT FEATURE PRINCIPLE. The method may also be applied to implement HPSG's binding theory.
As a testcase we improved upon the HPSG analysis of (Germanic) verb clusters and adjuncts by treating adjuncts as categories that are on the subcat list by virtue of a complex constraint. The fragment that has been implemented with the methods described is much larger than the discussion in the previous sections suggest, but includes treatments of extraposition, ipp, modal inversion, participium inversion, the third construction, partial-vp topicalisation, particle verbs, verb-second, subject raising, subject control, raising-to-object, object control and clitic climbing in Dutch.