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copied!<p>What the link above (http://www.michaelharrison.ws/weblog/?p=34) explains well is how this whole exercise is about avoiding the imperative programming (C, Java) need to declare two "holder" or "collector" variables ( or lists, vectors) explicitly in memory to catch your answers as you iterate through the list. With FP language Scheme's use of continuation, you do not "push" the test results as you step through (strawberries tuna and swordfish) into any separately created "baskets;" instead, you are consing together two lists as you send the appropriate consing functions -- one for eq? true, the other for eq? false -- through the recurs . . . finally ending up at the third col function which, in TLS's first example, is "a-friend" which asks whether the list built to hold all the matches is empty (null?). TLS then asks you to "run" multirember&co again with a new "last" col that merely asks the list containing all the "not tuna" atoms how many it contains ("last-friend"). So there are two "first class" functions being used to work with the task of collecting, i.e. building two separate lists, then at the end of the recursion unwinding, the original col ("a-friend") ask the final question. Maybe the name "multirember&co" is not the greatest name, because it really doesn't rebuild the list minus the atom to be removed; rather, it builds two separate lists -- which never get displayed -- then applies the final col (a-friend or last-friend) . . . which displays either #t or #f, or the length of the "not tuna" list.</p> <p>Here's some output:</p> <pre><code>> (multirember&co 'tuna '(and tuna) a-friend) #f > (multirember&co 'tuna '(and not) a-friend) #t </code></pre> <p>Here's a col to give back a list of non-matches:</p> <pre><code>(define list-not (lambda (x y) x)) </code></pre> <p>and its use:</p> <pre><code>> (multirember&co 'tuna '(and not) list-not) (and not) </code></pre>

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