Re: [Axiom-developer] pointers

[Tim Daly]

William,

a:='Fraction::SEX

is a lisp symbol. A lisp symbol is essentially the address of a data 
structure
which is approximately
   struct
      symbol-function (pointer to code)
      symbol-name (a string representation of the symbol)
      symbol-package (the lisp package (a hash table pointer))
      symbol-value (the value of the symbol)
      symbol-plist (an association list hanging on the symbol)

a:="Fraction"::Sex

is a lisp string, a contiguous set of bytes containing character code

So
a:=SYMBOL_-NAME('Fraction::SEX)$Lisp       (get the symbol-name from the 
fraction struct)
b:="Fraction"::SEX                                               (make a 
string of bytes containing "Fraction")
EQ(a,b)$Lisp ==> ()                                            (are they 
the same storage location? no)
c:=STRING_-EQUAL(a,b)$Lisp ==> T              (are they the same 
sequence of bytes? yes)

Tim



William Sit wrote:
> Hi Waldek:
>
> Thanks. That is exactly what I want. Good solution. So the
> "trick" is to use ' instead of the string. So is the
> following a bug?
>
> a:='Fraction::SEX
>   Fraction  Type:SExpression
> b:="Fraction"::SEX
>   Fraction  Type:SExpression
> (a=b)@Boolean
>   false     Type Boolean
>
> That is, I was deceived by the output which looked the same.
> Perhaps the output should have been ('Fraction) and
> ("Fraction") ??
>
> Also,
>
> destruct(a) or destruct(b) leads to an Error:
>
>  Function Selection for destruct
>       Arguments: SEX
>
>  [1]  signature:   SEX -> LIST SEX
>       implemented: slot (List $)$ from SEX
>
>
>    >> Error detected within library code:
>    Non-list
>
> protected-symbol-warn called with (NIL)
>
> William
>
>
> Waldek Hebisch wrote:
>   
> > William Sit wrote:
> >     
> > > Gabriel:
> > >
> > > Thanks for the response. Your script shows how to get the
> > > parameters, not the constructor. I do not have OpenAxiom
> > > installed (sorry). The question is whether I can test that
> > > the constructor is Fraction, or otherwise (like
> > > FiniteField) when the domain belongs to the category
> > > Field.
> > >
> > >       
> > Do you want something like this?
> >
> > (10) -> a := Fraction(Integer)
> >
> >    (10)  Fraction Integer
> >                                                                  Type: Domain
> > (11) -> (opOf(devaluate(a)$Lisp)$Lisp = 'Fraction::SEX)@Boolean
> >
> >    (11)  true
> >                                                                 Type: Boolean
> > (12) -> (opOf(devaluate(a)$Lisp)$Lisp = 'FiniteField::SEX)@Boolean
> >
> >    (12)  false
> >                                                                 Type: Boolean
> > (13) -> a :=FiniteField(5,2)
> >
> >    (13)  FiniteField(5,2)
> >                                                                  Type: Domain
> > (14) -> (opOf(devaluate(a)$Lisp)$Lisp = 'Fraction::SEX)@Boolean
> >
> >    (14)  false
> >                                                                 Type: Boolean
> > (15) -> (opOf(devaluate(a)$Lisp)$Lisp = 'FiniteField::SEX)@Boolean
> >
> >    (15)  true
> >                                                                 Type: Boolean
> >
> >
> > --
> >                               Waldek Hebisch
> > address@hidden
> >
> > _______________________________________________
> > Axiom-developer mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/axiom-developer
> >     
>
>