New to the group...

New to the group...

[Jason Meade]

Hi All,

My name's Jason. I'm new to Scheme, but am definitely a fan! It seems
to me that extensible and embeddable frameworks are the new
programming model for the 21st century. I'd like to see guile grow in
this respect, and am able to contribute however possible. :)

I've recently got guile 1.6 built from sources on my mac, and am
working on getting 1.8 set up on my freebsd machine.

Initially, I'd like to take a look at why guile bombs on recursive
algorithms. For example:

(define fact
  (lambda (n)
    (cond
     ((= n 1) 1)
     (else
      (* n (fact (- n 1)))))))

guile> (fact 69)
171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000
guile> (fact 70)
ERROR: Stack overflow
ABORT: (stack-overflow)

This does not seem right...  I can rework fact to use an accumulator,
but that seems a big kludgy, especially since I can run this same
program under chicken with an aguments well into the thousands without
any problems (aside from returning infinity as the result, that is!
;))

Anyway, I'm looking forward to learning more about this software.Thanks

-Jason


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Re: New to the group...

[David Pirotte]

On Wed, 3 May 2006 22:52:32 -0700
"Jason Meade" <jemeade@gmail.com> wrote:

Hi Jason,

you have the opportunity to look at (debug-options) and change the stack size
(debug-set! stack ...), see below

	http://www.gnu.org/software/guile/docs/docs-1.6/guile-ref/User-level-options-interfaces.html#User%20level%20options%20interfaces

> guile> (fact 70)
> ERROR: Stack overflow
> ABORT: (stack-overflow)

guile> (debug-options)
(show-file-name #t stack 20000 debug depth 20 maxdepth 1000 frames 3 indent 10 width 79 procnames cheap)

guile> (debug-set! stack 200000)
(show-file-name #t stack 200000 debug depth 20 maxdepth 1000 frames 3 indent 10 width 79 procnames cheap)


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Re: New to the group...

[Ludovic Courtès]

Hi,

"Jason Meade" <jemeade@gmail.com> writes:

> (define fact
>  (lambda (n)
>    (cond
>     ((= n 1) 1)
>     (else
>      (* n (fact (- n 1)))))))
>
> guile> (fact 69)
> 171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000
> guile> (fact 70)
> ERROR: Stack overflow
> ABORT: (stack-overflow)

Your definition of `fact' is not tail-recursive, i.e., for each
recursive call, a new stack frame is created.  In order to remove this
problem, you have to rewrite `fact' so that it is tail-recursive (which
means that the function returns immediately after the recursive call):
this way Guile will not create any new stack frame for the recursive
calls.

See for instance the definition of `tail-factorial' there:
http://sourceware.org/ml/guile/2000-06/msg00074.html .

Thanks,
Ludovic.


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Re: New to the group...

[Neil Jerram]

"Jason Meade" <jemeade@gmail.com> writes:

> My name's Jason. I'm new to Scheme, but am definitely a fan! It seems
> to me that extensible and embeddable frameworks are the new
> programming model for the 21st century. I'd like to see guile grow in
> this respect, and am able to contribute however possible. :)

Nice to meet you!

> Initially, I'd like to take a look at why guile bombs on recursive
> algorithms. For example:
>
> (define fact
>   (lambda (n)
>     (cond
>      ((= n 1) 1)
>      (else
>       (* n (fact (- n 1)))))))
>
> guile> (fact 69)
> 171122452428141311372468338881272839092270544893520369393648040923257279754140647424000000000000000
> guile> (fact 70)
> ERROR: Stack overflow
> ABORT: (stack-overflow)

This is a feature: if you write a program by mistake that recurses
forever using more and more stack, Guile will catch it for you.

If you'd like to disable this checking, just say (debug-set! stack 0).

Regards,
        Neil



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