; A variation that uses functional techniques to "Don't Repeat Yourself"
(define (sort L)
 (if (null L)
	NIL
	(let ((p (car L))); let p=(car L) in the following expressions
	 (append 
	  (sort (less_than p L))
	  (equal_to p L)
	  (sort (greater_than p L))
	 )
	)
))
(define (less_than p l) (extract (lambda (x) ( < x p) ) l ))
(define (equal_to p l) (extract (lambda (x) ( = x p) ) l ))
(define (greater_than p l) (extract (lambda (x) ( > x p) ) l ))
(define (extract f l )
 (cond
	((Null L)	NIL)
	((apply f (list (car L) )) (cons (car L) (extract f (cdr l))))
	(T	 (extract f (cdr l)))
))

 (trace SORT LESS_THAN EQUAL_TO GREATER_THAN EXTRACT)