Cleanup, added (promise?)

scheme/lazy.sld

@@ -5,48 +5,10 @@
     force 
     delay-force 
     make-promise 
-    ;promise?
+    promise?
   )
   (begin
-;    (define (make-promise x)
-;      (delay x))
-;  ;)
-;  ;(begin
-;    (define (promise? x)
-;      (and (pair? x)
-;           (null? (cdr x))
-;           (pair? (car x))
-;           (or (eq? #t (caar x))
-;               (and (eq? #f (caar x))
-;                    (procedure? (cdar x))))))
-;
-;  (define-syntax delay-force
-;    (er-macro-transformer
-;     (lambda (expr rename compare)
-;       `(,(rename 'promise) #f (,(rename 'lambda) () ,(cadr expr))))))
-;
-;  (define-syntax delay
-;    (er-macro-transformer
-;     (lambda (expr rename compare)
-;       `(,(rename 'delay-force) (,(rename 'promise) #t ,(cadr expr))))))
-;
-;  (define (promise done? proc)
-;    (list (cons done? proc)))
-;  (define (promise-done? x) (car (car x)))
-;  (define (promise-value x) (cdr (car x)))
-;  (define (promise-update! new old)
-;    (set-car! (car old) (promise-done? new))
-;    (set-cdr! (car old) (promise-value new))
-;    (set-car! new (car old)))
-;  (define (force promise)
-;    (if (promise-done? promise)
-;        (promise-value promise)
-;        (let ((promise* ((promise-value promise))))
-;          (if (not (promise-done? promise))
-;            (promise-update! promise* promise))
-;          (force promise))))))
 
-  ;; Delayed evaluation functions from husk
   (define force
       (lambda (object)
         (object)))
@@ -55,14 +17,11 @@
     (er-macro-transformer
      (lambda (expr rename compare)
        `(make-promise (lambda () ,(cadr expr))))))
+
   (define-syntax delay-force
     (er-macro-transformer
      (lambda (expr rename compare)
        `(make-promise (lambda () ,(cadr expr))))))
-  ;(define-syntax delay 
-  ;  (syntax-rules () 
-  ;    ((delay expression)
-  ;     (make-promise (lambda () expression)))))
 
   (define make-promise
     (lambda (proc)
@@ -77,4 +36,8 @@
                     (begin (set! result x)
                            (set! result-ready? #t)
                            result))))))))
+
+  ;; Not a very satisfying implementation, but would need to change
+  ;; how promises are stored to do better
+  (define promise? procedure?)
 ))