Proposal for stand-alone deriving declarations?

[Bjorn Bringert]

On http://hackage.haskell.org/trac/haskell-prime/wiki/ 
DerivedInstances it says:

"- There is no way to derive an instance of a class for a data type  
that is defined elsewhere (in another module)."

Though there is no proposal to fix this. Would such a proposal be  
appropriate for Haskell'?


If so, I propose to add a top-level declaration on the form:

'deriving' qtycls 'for' qtycon

which produces the same instance as a deriving clause in the  
declaration of the datatype or newtype would.


I have recently (thanks to the GHC Hackathon) implemented this in GHC.

/Björn