[m-dev.] proposal for promise_pure scope warning

[Julien Fischer]

On Tue, 15 Apr 2008, Ian MacLarty wrote:

> On Tue, Apr 15, 2008 at 9:26 AM, Peter Schachte
> <schachte at csse.unimelb.edu.au> wrote:
>>
>>>
>>>>  Well, either the author of the called predicate made it impure for a
>>>>  reason, in which case you shouldn't be promising that a call to the
>>>>  predicate is pure, or the author made a mistake and the predicate is
>>>>  actually pure, in which case it is the author's responsibility to
>>>>  fix the interface.  In any case the warning can always be disabled.
>>>>
>>>
>>
>>  Isn't it possible for one particular call to a generally impure predicate
>> to be pure?  Eg, with that particular argument list, it's pure.
>>
>
> I suppose so, but is this a good enough reason not to issue a warning?
> I've come across bugs where this warning would have helped twice now.
>
> Most of the warnings issued by the compiler have cases where they
> don't apply (consider for example too lax determinism warnings).  We
> still issue them, because often they are helpful. In the cases where
> the warning is inappropriate we usually either change the code or
> disable the warning if changing the code is not possible.
>
> I think the warning I'm proposing would be useful enough to be worth
> the slight inconvenience caused when it's not applicable.

You could always have the warning turned off by default.

I think you only want to emit a warning for promise_pure scopes around
impure goals that do not have any outputs and have determinism det or
cc_multi however.

Julien.
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