[Small-cl-src] Small, occasionally handy piece of code

;;; Haven't we all felt the need of generating combinations from a collection ;;; and calling a function for every combination? ;;; ;;; It's about as easy as this: ;;; <list> is the initial set ;;; <num> is the number of elements in the resulting combination ;;; <func> is the callback function (defun call-with-combination (list num func &optional acc) (declare (list list acc) (fixnum num) (function func)) (if (zerop num) (apply func acc) (loop for elt in list do (call-with-combination (remove elt list) (1- num) func (cons elt acc)))))