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Re: [Axiom-developer] pointers

 From: William Sit Subject: Re: [Axiom-developer] pointers Date: Mon, 09 Nov 2009 20:09:30 -0500

```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
```
```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/

```