Nondeterministic Lisp as a Substrate for Constraint Logic Programming

We have implemented a comprehensive constraint-based programming language as an extension to Common Lisp. This constraint package provides a uniied framework for solving both numeric and non-numeric systems of constraints using a combination of local propagation techniques including binding propagation, Boolean constraint propagation, generalized forward checking, propagation of bounds, and uniication. The backtracking facility of the nondeterministic dialect Common Lisp used to implement this constraint package acts as a general fallback constraint solving method mitigating the incompleteness of local propagation. An important aspect of our implementation is that it is both an extension to Common Lisp as well as fully implemented within Common Lisp. This is in contrast to recent constraint-based languages formulated in the logic programming framework which cannot be implemented eeciently in the language which they extend.