Permutation genetator in scheme

perm.scm

(define (empty? list)
   (eq? list '()))

(define (len list)
   (cond ((empty? list) 0)
         (else (+ 1 (len (cdr list))))))

(define (append list num)
  (cond ((empty? num) list)
        ((empty? list) (cons num '()))
        (else (cons (car list) (append (cdr list) num)))))

(define (last list)
  (cond ((empty? list) '())
        ((empty? (cdr list)) (car list))
        (else (last (cdr list)))))

(define (reverse list)
  (define (iter li rem)
    (cond ((empty? li) rem)
          (else (iter (cdr li) (cons (car li) rem)))))
  (iter list '()))

(define (del-last list)
  (define (iter li rem)
    (cond ((empty? li) rem)
          ((empty? (cdr li)) rem)
          (else (iter (cdr li) (cons (car li) rem)))))
  (reverse (iter list '())))

(define (concate l1 l2)
   (cond ((empty? l1) l2)
         (else (concate (del-last l1) (cons (last l1) l2)))))

(define (fc l1 l2)
  (concate (del-last l1) 
           (concate (cons (car (filter (lambda (x)(> x (last l1))) (reverse l2))) 
                          (filter (lambda (x)(<= x (last l1))) (reverse l2))) 
                    (cons (last l1) 
                          (cdr (filter (lambda (x)(> x (last l1))) (reverse l2)))))))

(define (fr l1 l2)
  (cond ((empty? l2) (fr (del-last l1) (cons (last l1) l2)))
        ((empty? l1) '())
        ((> (last l1) (car l2)) (fr (del-last l1) (cons (last l1) l2)))
        (else (fc l1 l2))))

(define (perm list)
  (cond ((empty? list) '())
        (else (cons list (perm (fr list '()))))))