Re: extending FEM enginering package with Guile

[rm]

On Mon, Jan 05, 2004 at 04:20:17PM -0300, Mario Storti wrote:
> 
>
> [...]                       But there is one point which I find too
> hard, and is the looping constructs. I think that explaining to the
> users concepts like tail-call recursion, or call/cc's is an
> overkill. I'm not speculating here, I have talked with many of them
> (those with better programming skills).  Perhaps such things may be
> used by the developers, but definitely not by the average user. There
> is the `while' special form, but even with this some simple looping
> constructs, like the following in C/C++

Well, scheme has a rather powerfull syntax facility, you can (and probably
should) write syntactic extensions that match your users needs/expectations.
With the help of macros (esp syntax-case e.a.) you can create your domain
specific "little language". After all, this is one of the reasons why
the FSF did choose scheme as their future embedable scripting language.

> while (cond0) {
>       // body1 0;
>       // ...
>       if (cond1) break;
>       // body 1
>       // ...
>       if (cond2) continue;
>       // body 2
>       // ...      
> }
> 
> are hard to write, due to the lack of `break' and `continue' in
> Scheme. I think that one can do that with catch/throw bu it also seems
> an overkill. I found some flame wars between some other Lisp dialects
> and Scheme and I anticipate that I'm not interested in starting such a
> discussion. So:

Flame wars aside, if there is a need for such a syntax it can be implemented.
Heinrich Taube (of Common Lisp Music fame) wrote a guile version of Common
Lisp's loop macro -- i think i once hacked up a guile module wrapper for it.
With that code you can do things like:

 (use-modules (clm iter))

 (define (all-squares-upto number)
   (loop for n in (iota number)
         collect (* n n)))

 (loop for language in '(perl python java cobol)
       do (format #f "~A sucks!" language))

 ;; break out of a loop
 (loop while (= (remainder (current-time ) 2) 0)
       do (format #t "Not yet ~%"))

 
etc. etc.
If you want i can try to find my wrapper and put it online.

 Ralf Mattes
> 
> Question 1: I ask simply if there is some simple way of writing code
> like this previous one in Scheme. 
> 
> Question 2: I have learned that in Scheme it is considered bad
> practice to `set!' variables, or in general to use side-effects. In
> our applications we manipulate huge structures (mainly vectors, sparse
> matrices, graphs, with sizes in the order of several hundredths MBs,
> and running for weeks), and it seems much more efficient to code this way
> (using side-effects). Am I right?
> 
> Question 3: Does anyone knows of some previous development regarding
> Guile/Scheme in a parallel environment? (I mean using message
> passing). 
> 
> Best regards,
> 
> Mario
> 
> -------------------------
> Mario Alberto Storti
> Centro Internacional de Metodos Computacionales
>   en Ingenieria - CIMEC (INTEC/CONICET-UNL)
> INTEC, Guemes 3450 - 3000 Santa Fe, Argentina
> Tel/Fax: +54-342-4511594
> e-mail: address@hidden
> http://www.cimec.org.ar/mstorti, http://www.cimec.org.ar
> -------------------------
> 
> 
> 
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