Add effect kind

Author: paf31

src/Control/Monad/Eff.purs

@@ -1,5 +1,6 @@
 module Control.Monad.Eff
-  ( Eff
+  ( kind Effect
+  , Eff
   , Pure
   , runPure
   , untilE, whileE, forE, foreachE
@@ -13,6 +14,17 @@ import Control.Monad (class Monad, ap)
 import Data.Functor (class Functor)
 import Data.Unit (Unit)
 
+-- | The kind of all effect types.
+-- |
+-- | Declare new effect types using `foreign data` declarations, as follows:
+-- |
+-- | ```purescript
+-- | import Control.Monad.Eff (kind Effect)
+-- |
+-- | foreign import data MyEffect :: Effect
+-- | ```
+foreign import kind Effect
+
 -- | The `Eff` type constructor is used to represent _native_ effects.
 -- |
 -- | See [Handling Native Effects with the Eff Monad](http://www.purescript.org/learn/eff/)
@@ -21,7 +33,7 @@ import Data.Unit (Unit)
 -- | The first type parameter is a row of effects which represents the contexts
 -- | in which a computation can be run, and the second type parameter is the
 -- | return type.
-foreign import data Eff :: # ! -> * -> *
+foreign import data Eff :: # Effect -> Type -> Type
 
 instance functorEff :: Functor (Eff e) where
   map = liftA1