[plt-scheme] equal? for native extension types [patch]

On Tue, 13 Feb 2007, Dimitris Vyzovitis wrote:

> equal? knows about some built-in types and structs -- and that's about 
> it. If you happen to define extension types with meaningful equality 
> tests, then you are stuck. Quite frustrating.

Hi Dimitris,

If structures are transparent, by setting their inspector appropriately, 
then equal? will work on them.

For example:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> (define-struct dummy (val) #f)
> (define x1 (make-dummy 1))
> (define x2 (make-dummy 2))
> (define x3 (make-dummy 1))
> (equal? x1 x3)
#t
> (equal? x1 x2)
#f
> (eq? x1 x3)
#f
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


See:

http://download.plt-scheme.org/doc/360/html/mzscheme/mzscheme-Z-H-4.html#node_sec_4.8

and:

http://download.plt-scheme.org/doc/360/html/mzscheme/mzscheme-Z-H-4.html#node_sec_4.5



Best of wishes!