Examples

On text is an case of the elementary POP-11 program:

define Double(Source) -> Effect; Source*2 -> Effect; enddefine;

Double(123) =>

This of these includes a few listings processing:

     define RemoveElementsMatching(Element, Source) -> Effect;
        lvars Stock;
        [%
           for Stock inside Source do
              unless Stock = Element or even Stock matches Element then
                 Stock;
              endunless;
           endfor;
        %] -> Effect;
     enddefine;

     RemoveElementsMatching("the", [the cat sat on the mat]) =>      ;;; outputs [cat sat on mat]
     RemoveElementsMatching("the", [[the cat] [sat on] the mat]) =>  ;;; outputs [[the cat] [sat on] mat]
     RemoveElementsMatching([= cat], [[the cat] is a [big cat]]) =>  ;;; outputs [is a]