[plt-scheme] Re: Using PLT Scheme libs elsewhere?

So when opening a port, you need to save a reference to it, rather
than just invoking the "open" function to provide a "port" argument
for a calling function.  That is, rather than

    (foo (open-input-file "bar"))

you would need to do

    (define iport (open-input-file "bar"))
    (foo iport)
    (close iport)

Unless, of course, foo *knows* it is supposed to close the port when
it is finished.

Right?  Or is there another way to approach this that would allow the
composition of these functions?


On May 20, 7:39 pm, Matthias Felleisen <matth... at ccs.neu.edu> wrote:
> On May 20, 2007, at 7:34 PM, SpinyNorman wrote:
>
> > Is the (UNLESS ...) vs. (IF (NOT...)) issue purely stylistic, or for
> > enhancing clarity for the poor schmo who has to read my code a month
> > from now, or would you expect a speed difference?
>
> Yes, it's for him. And he might be you. Promised. Try it out.
>
> ;; ---
>
> You want to close ports because some OSes don't support too many
> open ports at once. It's just something to get used to.
>
> -- Matthias
>
>
>
>
>
> > On May 18, 7:37 am, Matthias Felleisen <matth... at ccs.neu.edu> wrote:
> >> Thanks. I'd use UNLESS instead of (if (not blah) one-armed-if).
>
> >> On May 18, 2007, at 4:18 AM, Jens Axel Søgaard wrote:
>
> >>> Hi,
>
> >>> SpinyNorman wrote:
>
> >>>> Share?  I'm flattered.  Here it is, and my only claim at this
> >>>> point is
> >>>> that hey, it works.  Algorithmic insights are more than welcome.
>
> >>>> (require (lib "md5.ss"))
>
> >>> This md5.ss implements MD5 in Scheme. The Java MD5 is probably
> >>> implemented in C.
> >>> So if you switch to a C-based MD5 implementation, you'll get a
> >>> speedup. Here is
> >>> what to do:
>
> >>> (require (planet "digest.ss" ("soegaard" "digest.plt" 1 2)))
> >>> (require mzscheme)
>
> >>> (define test-string (make-string 10000))
>
> >>> (define (md-file-chunks port chunk-size)
> >>>  (let loop ()
> >>>    (begin
> >>>      (display (md5 (read-bytes chunk-size port)))
> >>>      (newline))
> >>>    (if (not (eof-object? (peek-byte port)))
> >>>    (loop))))
>
> >>> (md-file-chunks (open-input-string test-string) 1024)
>
> >>> See
> >>> <http://planet.plt-scheme.org/display.ss?
> >>> package=digest.plt&owner=soegaard>
> >>> for documentation.
>
> >>> This was tested on Windows, but ought to work elsewhere too.
> >>> You'll need a relatively new version of PLT Scheme, for
> >>> example 369.100.
>
> >>> It wasn't obvious whether you put the md-file-chunks in a module or
> >>> whether you are using the top-level. If you are using the top-level,
> >>> the line
>
> >>>    (require mzscheme)
>
> >>> makes sure primitive operations are inlined.
>
> >>> I'd love to hear your new timings.
>
> >>> PS: Remember to close file ports after use.
>
> >>> --
> >>> Jens Axel Søgaard
>
> >>> _________________________________________________
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>
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