;; DTrans.scm
;; NKU CSC 601 - Fall 2002 - Kirby
;; ----------------------------------------------------------------------
;; An example of a hack'n'eval Scheme program for making syntactic sugar.
;; (Usually macros do this.)
;; 
;; Allows an [allegedly] friendlier syntax for function definitions.
;; For example, one can write:
;; 
;;   (def cube (x)
;       (* x x x))
;;
;; instead of
;; 
;;   (define cube
;;      (lambda (s1 s2)
;;        (* x x x)))
;; ----------------------------------------------------------------------


(define dtrans
  (lambda (d)
    (if (eq? 'def (car d))  
        (let ((funcname (cadr d)) 
              (args-and-body (cddr d)))
          (eval (list 'define 
                      funcname 
                      (cons 'lambda args-and-body))))
        (eval d))))



;; Example usage
;; -------------

(map dtrans '(
              
  ;; Define functions the "new way".            
              
  (def longer? (s1 s2)
       (< (length s1) (length s2)))
  
  (def cube (x)
       (* x x x))
  
  (def tri-area (base height)
       (* base height))
  
  
  ;; dtrans allows traditional defs too.
  
  (define square
       (lambda (x) 
         (* x x))) 
  ))


(longer? '(a b c) '(a b c d e))
(longer? '(a b) '(c))
(cube 3)
(tri-area 10 10)
(square 9)