Exercise solution:
Generating a C-style compare function

 
(define (make-comparator lt)
 (lambda (e1 e2)
  (cond ((lt e1 e2) -1)
        ((lt e2 e1) 1)  ; notice the trick: we used lt with arguments reordered.
        (else 0))))

It can used in the following ways:

  > (define strcmp (make-comparator string<?))

  > (strcmp "abe" "kat")
  -1

  > (strcmp "kat" "abe")
  1

  > (strcmp "kat" "kat")
  0

Here is a function that generates a list of a 'less than', 'equal to', and 'greater than' from a C-style compare function:

 
(define (lt-eq-gt cmp)
  (list
     (lambda (x y)
        (< (cmp x y) 0))
     (lambda (x y)
        (= (cmp x y) 0))
     (lambda (x y)
        (> (cmp x y) 0))))