[Haskell-cafe] Re: FlexibleContexts and FlexibleInstances

[Isaac Dupree]

Claus Reinke wrote:
> if module 'A' exports multiparameter type classes, importers of those
> classes have to have MultiParamTypeClasses on - there are no legal
> uses of those imports otherwise (while FlexibleInstances/Contexts can
> just affect a subset of use sites).

say we have

module A where { class Coerce a b where coerce :: a -> b }
module B where { import A ; co a = coerce a }

Syntactically, module B doesn't require MultiParamTypeClasses because 
the signature that's involved is only discovered during type inference. 
  Something to beware of if those restrictions need to be implemented 
somehow in GHC.


Niklas Broberg wrote:
> If there is any interest, I can also propose these cases as bug reports to GHC.

please do!

-Isaac