The Direct LISP Approach to Function Environment Manipulation.

This paper reviews some of the control structures that have become popular in new extensions to LISP-based programming languages. A method for constructing these complex control structures that employs LISP features without the cost of double evaluation is developed. This technique, called the direct LISP approach, uses the LISP functions FUNCTION and EVAL to maintain and manipulate function access environments. Control environment manipulation is accomplished using continuation pointers and lambda expressions. This approach factors function execution into two distinct steps. First the function is associated with an environment and then it is invoked. The normal LISP evaluation routines retrieve the associated environments and apply the function. This method allows the programmer flexibility to design complex control structures without expensive overhead costs. Several examples that employ the direct LISP approach are presented and discussed. (Author)