[mercury-users] Working with exported types

[Peter Wang]

On 2006-07-27, Julien Fischer <juliensf at csse.unimelb.edu.au> wrote:
> 
> On Thu, 27 Jul 2006, Peter Wang wrote:
> 
> >On 2006-07-27, Ralph Becket <rafe at csse.unimelb.edu.au> wrote:
> >>Julien Fischer, Thursday, 27 July 2006:
> >>>Another approach that I have thought about adding (because doing the 
> >>>above
> >>>in the OpenGL binding was fairly tedious), is to add a foreign_enum 
> >>>pragma
> >>>that would allow you to safely use the values of Mercury enums on the 
> >>>other
> >>>side of the foreign language interface, something like:
> >>>
> >>>	:- type foo
> >>>		--->	foo
> >>>		;	bar
> >>>		;	baz
> >>>
> >>>	:- pragma foreign_enum("C", [
> >>>		foo - "FOO",
> >>>		bar - "BAR",
> >>>		baz - "BAZ"]).
> >>>
> >>>The compiler would then add the following to the modules .mh file:
> >>>
> >>>	#define FOO <representation of foo>
> >>>	#define BAR <representation of bar>
> >>>	#define BAZ (representation of baz>
> >>
> >>This would be an excellent addition to the FLI.
> >
> >Can we get something in the opposite direction as well?
> 
> What exactly do you mean?  The above also handles the opposite direction.

Does it?  I'm interested in importing C constants *into* Mercury,
without going through the contortions you've gone through in the OpenGL
binding.  At the moment the easiest way to do that is to hard-code the
value into the Mercury code, but that's brittle.  The second easiest way
is probably to introduce a foreign proc for each C constant, but that's
tedious.

Peter
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