[Haskell-cafe] Type constrain in instance?
jason.dusek at gmail.com
Fri Apr 9 12:16:58 EDT 2010
You need to define the instance with `ChainableFunction' and
not `CF' (the latter is value-level, not type level).
Once you make that switch, you'll find yourself with an
instance that is not compatible with the definition of the
Prelude Control.Category> :info Category
class Category cat where
id :: forall a. cat a a
(.) :: forall b c a. cat b c -> cat a b -> cat a c
-- Defined in Control.Category
We see that `id' and `.' have no class constraints and that
there is in fact no where to place a class constraint on `a',
`b' or `c'.
I think that what you're looking for are "restricted
categories" (and restricted monads and functors, as well,
perhaps). A cursory search suggests the `data-category'
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