Proposal for stand-alone deriving declarations?

Bjorn Bringert bringert at
Thu Oct 5 04:05:20 EDT 2006

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.


More information about the Haskell-prime mailing list