The dreaded M-R

Andrew Pimlott andrew at
Thu Feb 2 02:44:48 EST 2006

On Wed, Feb 01, 2006 at 10:32:26AM -0000, Simon Marlow wrote:
> On 31 January 2006 17:48, Andrew Pimlott wrote:
> > This indicates that the warning "wouldn't happen much" _when you want
> > sharing_.  But it would happen all the time when you don't want
> > sharing, eg. in the case Malcolm Wallace just posted.
> So you either add a type signature, or turn off the warning.

Right (provided you understand the warning).  Though I don't think many
people would turn off a default warning--it's just too much trouble.  (I
always add dummy definitions of coarbitrary to my Arbitrary instances,
rather than figure out how to suppress the undefined method warning.)
So in practice, I think most people would add a type signature.

> What's the problem?  

I've learned from this sub-thread that people oppose the M-R for at
different reasons.  Some dislike it on principle, or on aesthetic
grounds, and they would be happy to add a type signature.  But others
think it would be useful to define polymorphic variables without a type
signature, and they would not be happy to add one.

> I suspect you're saying that you don't want a warning by default, and
> you don't want the langage to recommend that compilers issue a warning
> by default, right?  If so, your objection is duly noted and I'll add the
> point to the wiki.



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