Compact lists are stored sequentially in memory, rather than chained with pointers. Since this is not always convenient, the Swym system permits a list to be chained, compact, or any combination of the two. A description is given of that list representation and the operators implemented (most are similar to those of LISP 1.5). The system garbage collector attempts to make all lists compact; it relocates and rearranges all of list storage using temporary storage. This unique list-compacting garbage collection algorithm is presented in detail. Several classes of the macros used to implement the system are described. Finally, consideration is given to those design factors essential to the success of a plex processing system implementation.