What do you mean by parameterized over a different type?
will c have a kind of * -> * ? I don't think it has to be for what you
want to work, but the idea of "same instance" will go out the window.
Do you have a small usage example?
On Wed, Feb 11, 2009 at 11:52 AM, John Lato
Hello,
I'm working on some code like the following:
class Chunkable c el | c -> el where cLength :: c -> Int cHead :: c -> Maybe el
I want to be able to map over this type, like this:
cMap :: Chunkable c' el' => (el -> el') -> c -> c'
but this isn't quite right. c' shouldn't be any instance of Chunkable, it should be the same instance except parameterized over a different type. Another approach would be something like:
class (Functor c) => Chunkable c el ...
except that's not right either. I think c has the wrong kind to be a Functor instance.
I expect there's something very basic I'm missing. Could anyone point in the proper direction of how to do this? Can this be expressed with associated types, perhaps?
Thanks,
John Lato _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe