;; DrScheme shrould be run using MzScheme language mode so that error 
;; is defined.  The details of using error are slightly different between 
;; MIT Scheme and MzScheme, but most error messages should work.

;; Allow name nil to be used for the empty list.
(define nil '()) 			

;; Some other constants with non-traditional names:
(define true #t)
(define false #f)

;; For stream programming section 3.5
;; We use the R5RS define force and delay which are slightly
;; different from the force and delay defined in the book:
;; delay (aka make-promise) handles recursive forcing.

(define the-empty-stream '())
(define stream-null? null?)
(define stream-car car)
(define (stream-cdr s)
  (force (cdr s)))

(define-syntax cons-stream
  (syntax-rules ()
    ((_ head tail)
     (cons head (delay tail)))))