default instance for IsString

[Tyson Whitehead]

On April 25, 2012 12:20:16 Johan Tibell wrote:
> On Wed, Apr 25, 2012 at 8:19 AM, Tyson Whitehead <twhitehead at gmail.com> 
wrote:
> > Is there a technical reason this couldn't be done?  The Haskell report
> > only says doing this is not part of haskell.  It doesn't say why.
> 
> I think the problem is incoherence, what if the same Map value got
> used with two different instances of Int?

I'm not sure I follow how allowing control over importing of instances could 
allow a programmer to define multiple instances for the same types.

I would have expected this to result in a link time error as a product of 
multiple declerations (something like a multiple symbol definition) regardless 
of whether any module brings it into scope as a possible candidate for use.

Cheers!  -Tyson