[Haskell-cafe] Re: Introducing Instances in GHC point releases

Simon Marlow marlowsd at gmail.com
Thu May 28 11:59:50 EDT 2009

On 27/05/2009 22:02, Henning Thielemann wrote:
> My proposal is thus: Discourage orphan instances! If you encounter that
> an instance is missing and it is a canonical one, it should be added to
> the package that defines the type or the class. If there are several
> choices for the implementation then the package where the instance would
> belong to should document that. Then programmers should find a consensus
> which of the choices they prefer. If you cannot wait for an official
> adaption of the required instance, then you must work with newtype
> wrappers.

Quite.  I argued the "no orphan instances in libraries" position on the 
libraries list last year, here's the start of the (longish) thread:


We ought to have a "guidelines for API design" section of the wiki 
somewhere, so we could put this in it.


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