Merge pull request #168 from turion/dev_monad_accum_instance

Generalise MonadAccum instance for AccumT

Author: sjshuck

Control/Monad/Accum.hs

@@ -83,6 +83,22 @@ module Control.Monad.Accum
   ( -- * Type class
     MonadAccum (..),
 
+    -- * The 'Accum' monad
+    Accum.Accum,
+    Accum.runAccum,
+    Accum.execAccum,
+    Accum.evalAccum,
+    Accum.mapAccum,
+
+    -- * The 'AccumT' monad transformer
+    Accum.AccumT (..),
+    Accum.execAccumT,
+    Accum.evalAccumT,
+    Accum.mapAccumT,
+    Accum.readerToAccumT,
+    Accum.writerToAccumT,
+    Accum.accumToStateT,
+
     -- * Lifting helper type
     LiftingAccum (..),
 
@@ -109,7 +125,6 @@ import qualified Control.Monad.Trans.Writer.CPS as CPSWriter
 import qualified Control.Monad.Trans.Writer.Lazy as LazyWriter
 import qualified Control.Monad.Trans.Writer.Strict as StrictWriter
 import Data.Functor (($>))
-import Data.Functor.Identity (Identity)
 import Data.Kind (Type)
 
 -- | The capability to accumulate. This can be seen in one of two ways:
@@ -160,7 +175,7 @@ class (Monoid w, Monad m) => MonadAccum w m | m -> w where
   {-# MINIMAL accum | look, add #-}
 
 -- | @since 2.3
-instance (Monoid w) => MonadAccum w (AccumT w Identity) where
+instance (Monoid w, Monad m) => MonadAccum w (AccumT w m) where
   look = Accum.look
   add = Accum.add
   accum = Accum.accum