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Programming in Emacs Lisp

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


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