Function: PIPE-PERMUTATIONS

Source

(defun pipe-permutations (p1)
  (if (pipe-null-p p1)
      (make-pipe nil empty-pipe)
      (pipe-mappend (lambda (e)
		      (pipe-map (lambda (p) (make-pipe e p))
				(pipe-permutations
				 (pipe-filter (lambda (f)
						(not (eq e f)))
					      p1))))
		    p1)))