Compilation and delayed evaluation in APL

Abstract

Most existing APL implementations are interpretive in nature, that is, each time an APL statement is encountered it is executed by a body of code that is perfectly general, i.e. capable of evaluating any APL expression, and is in no way tailored to the statement on hand. This costly generality is said to be justified because APL variables are typeless and thus can vary arbitrarily in type, shape, and size during the execution of a program. What this argument overlooks is that the operational semantics of an APL statement are not modified by the varying storage requirements of its variables.