How can I get all possible permutations of a list with Common Lisp?

Question

I\'m trying to write a Common Lisp function that will give me all possible permutations of a list, using each element only once. For example, the list \'(1 2 3) will give the ou

Answer 1

Here is the answer which allows repeated elements. The code is even more "lispish" as it doesn't use loop, with the disadvantage of being less comprehensible than Rainer Joswig's solution:

(defun all-permutations (lst &optional (remain lst))
  (cond ((null remain) nil)
        ((null (rest lst)) (list lst))
        (t (append
            (mapcar (lambda (l) (cons (first lst) l))
                    (all-permutations (rest lst)))
            (all-permutations (append (rest lst) (list (first lst))) (rest remain))))))

The optional remain argument is used for cdring down the list, rotating the list elements before entering the recursion.