[Axiom-developer] [#83 Bug 5977 1::DMP([x], FRAC INT)::POLY FRAC INT ==> 0] (new)

[Tim Daly]

William Sit <address@hidden> wrote:

> Martin wrote:
> 
> Thanks for investigating further.
>  
> > it might be that there is an error in mainVariable$SMP, but more likely, the
> > bug is earlier in the history. mainVariable$SMP is called from coerce$POLY,
> > interestingly without checking that the result of mainVariable might be
> > "failed".
> 
> Shouldn't that mean coerce$POLY should be fixed to check the "failed" case?

Sorry, my mistake. coerce$POLY checks itself whether there is a variable or 
not...

> Which coerce$POLY is that?

the coerce operation in the POLY domain.

> > (66) -> 1::DMP([x],FRAC INT)::POLY FRAC INT
> > 
> >    coerce$POLY
> >    mainVariable1$SMP
> >    mainVariable3$SMP
> >    mainVariable4$SMP
> >  LISP output:
> > 1
> >    coerce4$POLY
> >    1
> >    coerce5$POLY
> >    coerce6$POLY
> >    (66)  0
> >                           Type: Polynomial Fraction Integer

> > Is there a way to find out what exactly the variable p in mainVariable
> > contains?
> > 
> use p$Rep  ? or trace boot.

I'm pretty sure that the coercion to from DMP to POLY fails, without signalling 
an error, just like you could always do a "pretend". This would also explain 
(66)

Note that it is not possible to coerce a DMP or a UP or anything the like to a 
POLY in compiled code! Unfortunately I don't know where these interpreter 
coercions are coded. In any case, I'm convinced that they *should* be coded in 
the Algebra, not in the interpreter. 

> Now p is declared in multpoly.spad as Union(R, VPoly).
> So the code mainVariable p seems to be correct, but your debug info
> 
> > (65) -> 1::DMP([x],INT)::POLY INT
> > 
> >    coerce$POLY
> >    mainVariable1$SMP
> >    mainVariable3$SMP
> >    mainVariable4$SMP
> > 
> >    >> System error:
> >    Caught fatal error [memory may be damaged]
> > 
> > protected-symbol-warn called with (NIL)
> 
> suggests that when 1$DMP([x], INT) is passed on to coerce$(POLY INT) and then 
> to
> mainVariable$SMP as p, it is recognized as "case VPoly". So that must be where
> the bug is, in coerce$(POLY INT).

Note that coerce$POLY only coerces to OutputForm... No internal stuff done 
there. That's why I'm sure that it is an interpreter bug.


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