Re: [Axiom-developer] pointers

[William Sit]

Thanks, Tim. That is exactly what I am looking for. Now I 
would like to compare c.1 with some known constructor, say 
Fraction. (In other words, given a domain of category 
Field, I would like to know if it comes from the 
constructor Fraction). I tried a few variations and each 
time, Axiom says:

Although Fraction is the name of a constructor, a full 
type must be specified in the context you have used it. 
Issue )show Fraction for more information.

Things I tried:

a:=FiniteField(5,2)
b:=devaluate(a)$Lisp
c:=destruct(b)
c.1
d:="Fraction"::SExpression
e:Boolean
e:=EQ(c.1,d)  -- message above
e:=(c.1=Fraction)  -- message above
e:= (c.1=d$Lisp) -- message above
a1:=Fraction Integer
b1:=devaluate(a1)$Lisp
c1:=destruct(b1)
e:=(c.1=c1.1) -- message above

I confess that I'm still using a very old Window version 
(Version of Tuesday November 30, 2004 at 21:11:14) but I 
don't think that makes a difference in these examples.

William

On Mon, 09 Nov 2009 21:24:48 -0500
 Tim Daly <address@hidden> wrote:
> I'm not sure what you want. Perhaps you'd like to say:
>
> a:=Fraction(Polynomial(Integer))
> b:=devaluate(a)$Lisp
>
> which returns the list (actually of type SExpression)
>
> (Fraction (Polynomial (Integer)))
>
> c:=destruct(b)
> c.2
>
> which returns (Polynomial (Integer))
>
> Does that help?
>
> Tim
>
>
> William Sit wrote:
> > Tim:
> >
> > Interesting. Is there a similar function that is more 
> > structural? say, 
> > can I test whether some domain (which may be passed as a 
> > parameter of 
> > type Field) is of the form Fraction(something) and if so, 
> > extract 
> > "something" (that is, assign it to a variable and further 
> > test it), 
> > sort of a deconstruction?
> >
> > William
> >
> > On Mon, 09 Nov 2009 19:51:45 -0500
> > Tim Daly <address@hidden> wrote:
> > > You can get a memory pointer to a lisp object.
> > >
> > > a:=Fraction(Integer)
> > >
> > > returns the "memory location of Fraction(Integer)"
> > > You can prove this with
> > >
> > > b:=Fraction(Integer)
> > > EQ(a,b)$Lisp
> > >
> > > The lisp function EQ compares memory pointers.
> > >
> > > There is a lisp function to get the hash value of any 
> > > object
> > > call sxhash. You can call it.
> > >
> > > SXHASH(a)$Lisp
> > >
> > > Note that if
> > >
> > > c:=Integer
> > >
> > > then
> > > EQ(a,c)$Lisp is false
> > > SXHASH(a)$Lisp is not equal to SXHASH(c)$Lisp
> > >
> > > Thus the hash function you seek already exists.
> > > You just have to accept the fact that Spad is only 
> > > syntactic
> > > sugar for lisp code and lisp is not evil.
> > >
> > > Tim
> > >
> > >
> > >
> > > _______________________________________________
> > > Axiom-developer mailing list
> > > address@hidden
> > > http://lists.nongnu.org/mailman/listinfo/axiom-developer
> >
> > William Sit, Professor Emeritus
> > Mathematics, City College of New York 
> >                 Office: R6/202C 
> > Tel: 212-650-5179
> > Home Page: http://scisun.sci.ccny.cuny.edu/~wyscc/

William Sit, Professor Emeritus
Mathematics, City College of New York                  
Office: R6/202C Tel: 212-650-5179
Home Page: http://scisun.sci.ccny.cuny.edu/~wyscc/