APLELEGANCE—the art of staying within one's depth

Abstract

A barrier to the successful use of APL2 is the need to control the changes of depth which arise from using the operator each with functions such as enclose and disclose. The “spilt pepper” effect following a deluge of “each”'s can be just as damaging as the chains of left-brackets, and of quotes with their accompanying @@@@'s which are the sign of an ISO APL programmer losing his or her mental grip. The temptations of a fast interactive system as a substitute for thought are considerable, and should be resisted. To this end there are places in which informal perceptions of how APL2 functions and operators work can be more valuable than the formal descriptions given in the manuals, and this paper focuses on some points where such pedagogical issues arise. It consists of 4 sections, each with rules or precepts for the disciplined and controlled use of nestedness.