[racket] regexp-replace* with input-port ==> Re: multi-replace function

On Mon, Dec 6, 2010 at 11:15 PM, Eli Barzilay <eli at barzilay.org> wrote:

>
> One thing to keep in mind is that if you only care about replacing
> occurrences in some input file, then you can avoid the overhead of
> collecting the full text in memory.  For example, this will read the
> standard input, and replace each "~a" with a string from the list,
> spitting out the new text:
>
>  #lang racket/base
>  (require racket/generator)
>  (define get-string (generator () (for-each yield '("X" "Y" "Z"))))
>  (define (replace-all)
>    (when (regexp-match "~a" (current-input-port) 0 #f
> (current-output-port))
>      (display (get-string))
>      (replace-all)))
>  (replace-all)


This brings up something I noticed earlier today looking at regexp docs:
regexp-replace family does not work with input-port, when the other regexp-*
functions do.

Are there reasons for the difference?  Is it because input-port cannot be
written to?  But since the string & bytes variants all generate new output,
that will seem to be the same for input-port source anyways.

Thanks,
yc
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