Re: [Axiom-developer] pointers

[William Sit]

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
>
>
>
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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/