[Openmcl-devel] Applying sequence functions to a new type

[rm at fabula.de]

On Tue, Mar 01, 2005 at 05:52:41AM -0700, Gary Byers wrote:
> 
> On Mon, 28 Feb 2005, Andrew P. Lentvorski, Jr. wrote:
> 
> > This is probably a really stupid question, but how do I define the
> > sequence functions so that they apply to a new class?
> 
> You basically can't reliably subclass BUILT-IN-CLASSes like SEQUENCE
> (or FLOAT or FIXNUM) in CLOS.

Is this a limitation of CLOS or an artefact of the implementation of BUILT-
IN-CLASSes? 

> The standard sequence functions are not necessarily GENERIC-FUNCTIONs
> (they aren't in OpenMCL or in any other implementation I'm aware of),
> so you can't extend their behavior by adding methods on them.

But that at least is open to the implementation - it _would_ be possible
to have the sequence functions as GENERIC-FUNCTIONs.

> There are object systems (I believe that this is true to a large
> degree of SmallTalk) in which there's no concept of a non-extensible
> BUILT-IN-CLASS and in which all functions are (conceptually, at least)
> something like GENERIC-FUNCTIONs, but CLOS is not such a system.

AFAIK it's possible to do so in guile's GOOPS (which is rather close
to CLOS :-) by doing:

 (enable-primitive-generic! <buildin-function>)

So one can enable GENERIC-FUNCTIONality per build-in function. Off course
it's more expensive to change a build-in into a generic but since one can
do so for individual functions there's a lot of control.

 Cheers  RalfD
 
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