Composing recursive logic programs withClausal join

A family of methods for composing logic programs from simpler components is presented. Specifically, simple pairs of programs operating on lists, trees and other recursive structures are composed to generate a single program with composite functionality. The methods are based onclausal join, a specific sequence of unfold/fold transformations for deriving a new clause from a given pair of clauses and a join specification.Procedural join composes a new procedure from two given procedures by applyingclausal join to all pairs of their clauses.1-1 Join composes a new procedure from closely related procedures by applyingclausal join to corresponding pairs only.Meta join is a modification of1-1 join for composing meta-interpreters. The transformations are straightforward to implement in Prolog, as is demonstrated in the paper.