[Haskell-cafe] MPTC inheritance
paul at cogito.org.uk
Tue Feb 24 14:41:08 EST 2009
Derek Gladding wrote:
> Please forgive me if I'm still mentally contaminated by the OO way of
> seeing (and discussing) the universe, but I'm trying to figure out how
> to "inherit an interface" from a multi-parameter type class.
> but this isn't allowed (kind mismatch).
Kinds are a meta-type system for types. Because Haskell has such a rich
type system, the types themselves need a type-like system. These are
"kinds". You never declare kinds (apart from certain language
extensions not in use here): the compiler infers them.
This suggests that your problem is in the types lower down. Probably
you are using "a" or "b" in a way that implies they take a type argument
in one place (kind * -> *) and not in another place (kind *).
More information about the Haskell-Cafe