Scope, assumptions, asksign, context. Was Re: Bug in Maxima 5.30.0

It might not be a bad idea for some ambitious person to re-examine the whole
assume / database / deduction/ context ball of wax.  The original author 
(Michael Genesereth)
is at Stanford.  Probably not interested in hearing about problems with it..

Scope in Maxima has several nasty aspects.  For example, scope of 
bindings during pattern
matching vs scope of bindings in function calls vs. simplifcation rules 
vs. global bindings; also
bindings of properties.  e.g.
assume(x>0)  block([x],assume(x<0), is (x>0))  returns true.


Integration isn't the only place where local knowledge is requested 
and/or generated.  If
we can fix it there, it may pay to look at  (for example) simplification 
of sums, solve,
and who knows where else.

RJF


On 8/30/2013 10:50 AM, Stavros Macrakis wrote:
> It is clearly wrong to have $sign call clearsign -- sign/asksign 
> results are supposed to be persistent across a single user interaction 
> (%i/%o -- see suprv1/meval*).  This makes sense because the user has 
> no way of knowing what internal/local scope they might be in.
>
> If a more local scope is wanted for a sign/asksign result, it should 
> be handled using the context mechanism.  I suppose you could try to do 
> it also using unwind-protect etc., but that is tricky to get right. 
>  For example, I see that compar/asksign-p-or-n has a bug where if it 
> is previously assumed that not equal(x,0), then (asksign-p-or-n x) 
> will /remove/ that preexisting assumption.
>
> I suppose there may be cases where the caller really knows that the 
> result should not be persistent, and could call sign-plus-cleanup, but 
> that seems like a really bad idea in general.
>
>          -s
>
>
>
> On Fri, Aug 30, 2013 at 12:52 PM, Robert Dodier 
> <robert.dodier at gmail.com <mailto:robert.dodier at gmail.com>> wrote:
>
>     On 2013-08-30, Raymond Toy <toy.raymond at gmail.com
>     <mailto:toy.raymond at gmail.com>> wrote:
>
>     >     3137b946bed77dc4311e4266ed338cd2d46d299f is the first bad commit
>     >     commit 3137b946bed77dc4311e4266ed338cd2d46d299f
>     >     Author: robert_dodier <robert_dodier at users.sourceforge.net
>     <mailto:robert_dodier at users.sourceforge.net>>
>     >     Date:   Thu Mar 21 16:03:43 2013 -0700
>     >
>     >         Call CLEARSIGN from $SIGN to clean up facts introduced
>     by sign functions.
>     >
>     > All versions before this commit are fine; you only have to
>     answer one
>     > question and the integral is evaluated correctly.  All versions
>     after this
>     > version are bad; you have to answer several questions and the
>     integral
>     > is not evaluated.
>
>     Hrm. That change was made to counteract some other strange behavior --
>     'sign' left some facts floating around after it was called. Without
>     looking at the integration code, my guess is that it is assuming the
>     sign fact persists for the duration of the integration. Should
>     there be
>     separate sign-plus-cleanup and sign-with-no-cleanup functions? It
>     hurts
>     my head a little bit but maybe so ....
>
>     Thanks for looking into it --
>
>     Robert Dodier
>
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