John Meacham wrote:
every single parameter type class whole parameter is of kind * class Foo a where
automatically declares a data type defined as
data Foo = exists a . Foo a => Foo_ a (where Foo_ is some internal, non user accessable name)
and an instance
instance Foo Foo where method (Foo_ x) = method x ...
I don't much like this, it seems like unnecessary sugar to me. My first preference would be not to do this at all. My second preference would be to do this a bit more generally: every type class class Foo a b c where automatically declares a data type defined as data Foo t = exists a b c . Foo a b c => Foo_ (t a b c) (where Foo_ is some internal, non user accessable name) every single parameter type class whole parameter is of kind * declares an instance instance Foo (Foo Identity) where method (Foo_ x) = method x ... It's still pretty ugly. I don't like special-casing classes that happen to have a particular kind signature. -- Ashley Yakeley