[mercury-users] Request for comments on this code

[Julien Fischer]

On Tue, 11 Jul 2006, Peter Schachte wrote:

> On Tue, Jul 11, 2006 at 01:47:42PM +1000, Julien Fischer wrote:
>> On Mon, 10 Jul 2006, Peter Schachte wrote:
>>> With && you're saying the code is pure and
>>> order doesn't matter, but just for operational reasons we want the
>>> code before the && to complete before starting the code after it.  But
>>> in that case, why is this so rigid?  Isn't && only advisory?
>>
>> What would be the point of it if it were only advisory?
>
> Telling Mercury a preferred order for two goals.  A suggestion to the
> compiler.
>
> I guess the question really is to what extent you trust the compiler.
> If the compiler gets clever and discovers that in some mode it's
> better to execute those goals in the opposite order, why shouldn't it
> reorder them?  We're stipulating that this isn't a question of
> correctness, just performance.  And if you've specified a mode for a
> predicate that requires the goals be reordered, I'd rather have it
> reorder the goals, perhaps with a warning, than to refuse to compile.
>
> What do you want && for?

I don't (at the moment) - I was merely commenting on your question of how 
such a construct would handle functions in the head of a clause.

Mark gave an example of where && would be useful (make sure that labelling
only happens after posting constraints in code that uses solver types)
further back in this thread (somewhere).

Julien.
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