[m-dev.] Initialisation of solver type variables

Fergus Henderson fjh at cs.mu.OZ.AU
Mon Apr 26 07:19:40 AEST 2004

On 22-Apr-2004, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> [I've just discussed this with Peter and Maria, but thought it would be
> worth posting to the list in case anyone else has a comment to make.]
> If `X' belongs to a solver type and is `free' and appears as a mode
> `(any >> ...)' argument in the call `p(..., X, ...)' then the Mercury
> compiler first initialises by transforming
> 	p(..., X, ...)
> into
> 	<<call initpred>>(X),
> 	p(..., X, ...)
> It occurred to me that the compiler should also append calls to
> `initpred' for output variables that should have inst `any' but
> are in fact `free'.

At the end of the clause body, you mean?
Sounds reasonable, assuming that there is an explicit mode declaration.


	:- mode p(..., free >> any, ...).
	p(..., Y, ...) :-
		... code which leaves Y free ...

would become

	:- mode p(..., free >> any, ...).
	p(..., Y, ...) :-
		... code which leaves Y free ...,
		<<call initpred>>(Y).

If there's no explicit mode declaration, then it may be better
to infer the mode free >> free rather than free >> any.

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