The dreaded M-R

Lennart Augustsson lennart at
Mon Jan 30 22:02:22 EST 2006

Andrew Pimlott wrote:
> On Tue, Jan 31, 2006 at 12:52:51AM +0000, Neil Mitchell wrote:
>>>Second, a warning about "loss of sharing" may befuddle beginners (who
>>>are usually not taught to write type signatures at the start).
>>Are standards documents the place for prescribing which warnings
>>should be raised, and under what circumstances?
>>If someone is using GHC, and has specified -O2 then clearly something
>>that causes vastly more time is a problem. If someone is learning
>>Haskell and is using Hugs then they probably couldn't care less.
>>Perhaps some warnings should be left up to the implementation to
> My ultimate point was that the possibility of a warning should carry
> very little weight (if any) when analyzing the pros and cons of a
> language change.  If you want to argue that a warning would mitigate a
> disadvantage of a change, you need to think about when the warning would
> be emitted, which I agree should be outside the scope of a standards
> discussion.  So I am just suggesting that we simplify the discussion by
> not talking about warnings (which suggestion I will follow as soon as I
> hit send!).

I agree that a requiring a warning in the language standard is a rather
dodgy thing.  So let's say we don't have a warning.  Is this a tried
solution?  Yes, nhc does exactly that.  It does not have the M-R nor
a warning.  And I have never heard outcries about how bad nhc is because
of this.

	-- Lennart

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