[m-dev.] adding promise_only_solution

[Fergus Henderson]

On 06-Nov-1998, Peter Schachte <pets at cs.mu.OZ.AU> wrote:
> > As I mentioned at the last Mercury meeting, I'm planning
> > on adding `promise_only_solution' to the Mercury standard
> > library before the upcoming release.  One thing I haven't
> > figured out, though, is exactly where to put it.
> > One possibility is a new module, called say `promise.m'.
> > Another possibility is to add it to builtin.m.
> 
> Ultimately, I think a prettier (and more efficient) way to make such a
> promise should become part of the language proper, so I'd argue it
> should go in builtin.m.

Well, as the following comment in builtin.m implies, we're kind of
phasing out the practice of defining predicates in builtin.m:

|	% PREDICATES.
|
|	% Most of these probably ought to be moved to another
|	% module in the standard library such as std_util.m.

In the end it doesn't really matter much either way,
it's six of one and half a dozen of the other...
I'm inclined to stick with std_util.m but it's not a strong
preference.

> If/when it gets compiler support, then
> existing code would continue to work, but new code wouldn't need messy
> lambdas and packaging up of multiple outputs.

If/when it gets compiler support, we'll add 

	:- pragma obsolete(promise_only_solution/1).

of course ;-)

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>  |  of excellence is a lethal habit"
PGP: finger fjh at 128.250.37.3        |     -- the last words of T. S. Garp.