Am Donnerstag 23 April 2009 19:15:05 schrieb Marco Túlio Gontijo e Silva:

Hello,

I read the type families example at http://haskell.org/haskellwiki/GHC/Indexed_types and I wanted to do something similar to the Collects example, but using a type of kind * ->

*:

...

class StateFunctor sf where type SFMonad sf type SFValue sf sfmap :: (SFValue sf -> SFValue sf) -> sf -> SFMonad sf ()

I wrote the instance as:

...

instance StateFunctor (ListStore a) where type SFMonad (ListStore a) = IO type SFValue (ListStore a) = a sfmap function listStore = listStoreGetSize listStore >>= listStoreSfmap function listStore

listStoreSfmap :: (a -> a) -> ListStore a -> Int -> IO () listStoreSfmap _function _listStore 0 = [] listStoreSfmap function listStore size = listStoreGetValue listStore index

>>= listStoreSetValue listStore index . function

...

...

listStoreSfmap function listStore index

where index :: Int index = pred size

I'm getting:

DistroCreator/GUI/List.hs:51:47: Kind error: `SFMonad' is applied to too many type arguments In the type `SFMonad sf ()' In the type `sf -> SFMonad sf ()' In the type `(SFValue sf -> SFValue sf) -> sf -> SFMonad sf ()' Failed, modules loaded: none.

How can I use type families with types * -> *?

For example: ----------------------------------- {-# LANGUAGE TypeFamilies, KindSignatures #-} module TypeF where data ListStore a = Dummy listStoreGetSize = undefined listStoreSfmap = undefined class StateFunctor sf where   type SFMonad sf :: (* -> *)   type SFValue sf   sfmap :: (SFValue sf -> SFValue sf) -> sf -> SFMonad sf () instance StateFunctor (ListStore a) where   type SFMonad (ListStore a) = IO   type SFValue (ListStore a) = a   sfmap function listStore     = listStoreGetSize listStore >>= listStoreSfmap function listStore ------------------------------------- Prelude> :l TypeF [1 of 1] Compiling TypeF ( TypeF.hs, interpreted ) Ok, modules loaded: TypeF.

Greetings.