Merge pull request #3 from purescript/class

Move MonadEff over

README.md

@@ -14,3 +14,4 @@ bower install purescript-eff
 
 - [Control.Monad.Eff](docs/Control.Monad.Eff.md)
 - [Control.Monad.Eff.Unsafe](docs/Control.Monad.Eff.Unsafe.md)
+- [Control.Monad.Eff.Class](docs/Control.Monad.Eff.Class.md)

docs/Control.Monad.Eff.Class.md

@@ -0,0 +1,26 @@
+## Module Control.Monad.Eff.Class
+
+#### `MonadEff`
+
+``` purescript
+class (Monad m) <= MonadEff eff m where
+  liftEff :: forall a. Eff eff a -> m a
+```
+
+The `MonadEff` class captures those monads which support native effects.
+
+Instances are provided for `Eff` itself, and the standard monad transformers.
+
+`liftEff` can be used in any appropriate monad transformer stack to lift an action
+of type `Eff eff a` into the monad.
+
+Note that `MonadEff` is parameterized by the row of effects, so type inference can be
+tricky. It is generally recommended to either work with a polymorphic row of effects,
+or a concrete, closed row of effects such as `(trace :: Trace)`.
+
+##### Instances
+``` purescript
+instance monadEffEff :: MonadEff eff (Eff eff)
+```
+
+

src/Control/Monad/Eff/Class.purs

@@ -0,0 +1,24 @@
+module Control.Monad.Eff.Class 
+  ( MonadEff
+  , liftEff
+  ) where
+
+import Prelude
+
+import Control.Monad.Eff
+
+-- | The `MonadEff` class captures those monads which support native effects.
+-- |
+-- | Instances are provided for `Eff` itself, and the standard monad transformers.
+-- |
+-- | `liftEff` can be used in any appropriate monad transformer stack to lift an action
+-- | of type `Eff eff a` into the monad.
+-- |
+-- | Note that `MonadEff` is parameterized by the row of effects, so type inference can be
+-- | tricky. It is generally recommended to either work with a polymorphic row of effects,
+-- | or a concrete, closed row of effects such as `(trace :: Trace)`.
+class (Monad m) <= MonadEff eff m where
+  liftEff :: forall a. Eff eff a -> m a
+
+instance monadEffEff :: MonadEff eff (Eff eff) where
+  liftEff = id