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From: ludovic.courtes@laas.fr (Ludovic Courtès)
Cc: guile-devel@gnu.org
Subject: Re: New to the group...
Date: Thu, 04 May 2006 15:08:51 +0200	[thread overview]
Message-ID: <87odye9bto.fsf@laas.fr> (raw)
In-Reply-To: <9c4a82e00605032252u3687bb76ybe033f3c5de5d44b@mail.gmail.com> (Jason Meade's message of "Wed, 3 May 2006 22:52:32 -0700")

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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  parent reply	other threads:[~2006-05-04 13:08 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2006-05-04  5:52 New to the group Jason Meade
2006-05-04  6:33 ` David Pirotte
2006-05-04 13:08 ` Ludovic Courtès [this message]
2006-05-04 15:57 ` Neil Jerram

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