[Maxima] How to prevent evaluation.

[Barton Willis]

The code for the simplifying %if is in
share/contrib/to_poly_solve_extra.lisp,
and user documentation is share/contrib/to-poly-user-doc.html.

The function %if evolved to make the to_poly_solver work the way I
wanted it to. My intention wasn't to write the ultimate simplifying
conditional. I invite everybody to examine the code for %if and make
it better. Of course, it would be great if better didn't break
to_poly_solve :)

Barton

-----maxima-bounces at math.utexas.edu wrote: -----

>To: Richard Hennessy <rich.hennessy at verizon.net>
>From: Richard Fateman <fateman at cs.berkeley.edu>
>Sent by: maxima-bounces at math.utexas.edu
>Date: 12/27/2009 05:42PM
>cc: Maxima List <maxima at math.utexas.edu>
>Subject: Re: [Maxima] How to prevent evaluation.
>
>Richard Hennessy wrote:
>>
>>
>>     It seems like in the %if function both the then part and the else
>>     part are always expanded even when only one needs to be evaluated.
>>
>Maybe you could review what it is that %if does, and see if it is
>consistent with the semantics of %if to evaluate only one part?
>I expect that it is not. But I've forgotten how %if is supposed to work
>and it isn't in the documentation I have.
>
>
>>       Is there a way to stop evaluation of both parts
>>
>
>Certainly, but then it would be a different facility. Which do you
>want?  Also, Maxima generally is incapable of
>avoiding a calculation because it might take too long. It can, of
>course, stop a calculation  after it has taken a while.
>But not usually anticipating...
>
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