Consider a categorial treatment of subject-verb agreement with intransitive and transitive verbs defined as follows:
Subject-verb agreement can be incorporated easily if one reduces agreement to a form of subcategorization. If, however, one wishes to distinguish these two pieces of information (to avoid a proliferation of subcategorization types or for morphological reasons, for instance), it is not obvious how this could be done without recursive constraints. For intransitive verbs one needs the constraint that arg agr = Agr (where Agr is some agreement value), for transitive verbs that val arg agr = Agr, and for ditransitive verbs that val val arg agr = Agr. The generalization is captured using the recursive constraint sv_agreement (2). In (2) and below, we use definite clauses to define lexical entries and constraints. Note that lexical entries relate words to feature structures that are defined indirectly as a combination of simple constraints (evaluated by means of unification) and recursive constraints.
Relational constraints can also be used to capture the effect of lexical rules. In a lexicalist theory such as CG, in which syntactic rules are considered to be universally valid scheme's of functor-argument combination, lexical rules are an essential tool for capturing language-specific generalizations. As Carpenter  observes, some of the rules that have been proposed must be able to operate recursively. Predicative formation in English, for instance, uses a lexical rule turning a category reducible to VP into a category reducing to a VP-modifier . As a VP-modifier is reducible to VP, the rule can (and sometimes must) be applied recursively.