(Previous discussion continued)
Re: simpler srfi 45 implementation AndrevanTonder 14 Nov 2007 13:41 UTC

Re: simpler srfi 45 implementation AndrevanTonder 14 Nov 2007 13:41 UTC

Just to avoid confusion.

   This version is not safe for space and
   does not implement SRFI-45.

Andre

On Wed, 14 Nov 2007, Phil Bewig wrote:

> Here is the code for stream-type, extracted from the latest version of
> SRFI-45 (at this writing, that version has been submitted to the editors but
> has not yet appeared on srfi.schemers.org).
>
>  (define-record-type (stream-type make-stream stream?)
>    (fields (mutable box stream-promise stream-promise!)))
>
>  (define-syntax stream-lazy
>    (syntax-rules ()
>      ((stream-lazy exp) (make-stream (lambda () exp)))))
>
>  (define-syntax stream-delay
>    (syntax-rules ()
>      ((stream-delay exp) (stream-lazy (make-stream (list exp))))))
>
>  (define (stream-force prom)
>    (let ((p (stream-promise prom)))
>      (cond ((pair? p)   (car p))
>            ((stream? p)
>              (let ((x (stream-force p)))
>                (let ((content (stream-promise prom)))
>                  (if (pair? content) (cdr content)
>                      (begin (stream-promise! prom (list x)) x)))))
>            ((procedure? p)
>              (let ((prom* (p)))
>                (if (not (pair? (stream-promise prom)))
>                    (if (stream? prom*)
>                        (begin (stream-promise! prom (stream-promise prom*))
>                               (stream-promise! prom* prom))
>                        (stream-promise! prom (list prom*))))
>                (stream-force prom)))
>            (else (error 'stream-force "invalid promise")))))