First, REC stands for regular expression compiler, a rather fanciful term concocted one day when the program had to be given a name. Anyway the idea was to make programs follow the style of regular expressions, using elements of concatenation, selection of alternatives, and iteration. It was created for the purpose of completing an acceptance test for a PDP-8 (and consequently had to be very compact) on the basis of earlier work with ``operator predicates'' in LISP .