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Recursive Pattern: accumulate

Another recursive pattern is called the accumulate pattern. In the accumulate recursive pattern, an action is performed on every element of a list and the result of that action is accumulated with the results of performing the action on the other elements.

This is very like the `every' pattern using cons, except that cons is not used, but some other combiner.

The pattern is:

Here is an example:

     (defun add-elements (numbers-list)
       "Add the elements of NUMBERS-LIST together."
       (if (not numbers-list)
           0
         (+ (car numbers-list) (add-elements (cdr numbers-list)))))
     
     (add-elements '(1 2 3 4))
         ⇒ 10

See Making a List of Files, for an example of the accumulate pattern.