Finite Automata Theory Based Optimization of Conditional Variable Binding

We present an efficient and highly optimized implementation of destructuring-case in Common Lisp.  This macro allows the selection of the most appropriate destructuring lambda list of several given based on structure and types of data at run-time and thereafter dispatches to the corresponding code branch.  We examine an optimization technique, based on finite automata theory applied to conditional variable binding and execution, and type-based pattern matching on Common Lisp sequences.  A risk of inefficiency associated with a naive implementation of destructuring-case is that the candidate expression being examined may be traversed multiple times, once for each clause whose format fails to match, and finally once for the successful match.  We have implemented destructuring-case in such a way to avoid multiple traversals of the candidate expression.  This article explains how this optimization has been implemented.