Re: [Axiom-developer] pointers

[Tim Daly]

I'm not sure what you are asking. Are you having trouble with working in 
the SExpression domain?
You can move the SExpressions out to other domains. Sometimes it is 
painful but it works. So:

a:=FiniteField(5,2)
b:=devaluate(a)
string(SYMBOL_-NAME(b.1)$Lisp) ==> "FiniteField" (of type String)
integer(b.1) ==> 5  (of type PositiveInteger)

Does this help?

Tim


William Sit wrote:
> It appears that to test the constructor, one must test a candidate 
> against a known one via the constructor itself, and not be "fiat" by 
> using a SExpression. Is this related to hashing of pointers? 
> Continuing with script in the previous email (attached):
>
> (11) -> EQ(c.1,d)$Lisp
>
>    (11)  ()
>                                                            Type: 
> SExpression
> (12) -> EQ(c1.1,d)$Lisp
>
>    (12)  ()
>
> Type: SExpression
> -- So EQ$Lisp returns () in both cases, even for -- EQ(c.1,c1.1)$Lisp
>
> -- (19)  ()
>                                                            --Type: 
> SExpression
>                                                           
> (13) -> e:=(c.1=d)
>
>    (13)  false
>                                                                Type: 
> Boolean
>
> (14) -> e:=(c1.1=d)
>
>    (14)  false
>                                                               Type: 
> Boolean
> -- same problem with = using SExpression.
> 15) -> e:=(c1.1=c1.1)
>
>    (15)  true
>                                                                Type: 
> Boolean
> (16) -> d
>
>    (16)  Fraction
>                                                            Type: 
> SExpression
> (17) -> c1.1
>
>    (17)  Fraction
>                                                            Type: 
> SExpression
>
> So it seems there is some distinction: d (defined explicitly as 
> Fraction::SExpression) is different from c1.1 defined using 
> devaluate/destruct from a domain. A user should not need to know the 
> various way "equal" is tested if the two arguments for "equal" come 
> from the same domain SExpression. So is this a bug?
>
> William
>
> On Tue, 10 Nov 2009 12:00:58 -0500
>  "William Sit" <address@hidden> wrote:
> > Tim:
> >
> > Sorry about the last message, please ignore.
> > The problem is solved (I was simply not being careful) and made some 
> > false claims on the results.
> >
> > (16) -> )clear all
> >    All user variables and function definitions have been cleared.
> > (1) -> a:=FiniteField(5,2)
> >
> >    (1)  FiniteField(5,2)
> >                                                          
> >      Type: Domain
> > (2) -> b:=devaluate(a)$Lisp
> >
> >    (2)  (FiniteField 5 2)
> >                                                          
> >  Type: SExpression
> > (3) -> c:=destruct(b)
> >
> >    (3)  [FiniteField,5,2]
> >                                                        Type: List 
> > SExpression
> > (4) -> c.1
> >
> >    (4)  FiniteField
> >                                                          
> >  Type: SExpression
> > (5) -> d:="Fraction"::SExpression
> >
> >    (5)  Fraction
> >                                                          
> >  Type: SExpression
> > (6) -> e:Boolean
> >                                                          
> >        Type: Void
> > (7) -> e:=EQ(c.1,d)$Lisp
> >
> >    (7) ()
> >                                                     Type: SExpression
> > (7) -> e:=(c.1=Fraction) -- message above
> >
> >    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.
> > (7) -> e:= (c.1=d$Lisp)
> >
> >    >> System error:
> >    The variable |d| is unbound.
> >
> > protected-symbol-warn called with (NIL)
> > (7) -> a1:=Fraction Integer
> >
> >    (7)  Fraction Integer
> >                                                          
> >      Type: Domain
> > (8) -> b1:=devaluate(a1)$Lisp
> >
> >    (8)  (Fraction (Integer))
> >                                                          
> >  Type: SExpression
> > (9) -> c1:=destruct(b1)
> >
> >    (9)  [Fraction,(Integer)]
> >                                                        Type: List 
> > SExpression
> > (10) -> e:=(c.1=c1.1)
> >
> >    (10)  false
> >                                                          
> >     Type: Boolean
> >
> > William
> > ----
> >
> > On Tue, 10 Nov 2009 11:38:25 -0500
> >  "William Sit" <address@hidden> wrote:
> > > 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/
> >
> > 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/