monoids-0.1.2: Data/Monoid/Monad/State/Strict.hs

{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE FlexibleInstances, MultiParamTypeClasses #-}

module Data.Monoid.Monad.State.Strict
    ( module Control.Monad.State.Strict
    , module Data.Monoid.Reducer
    )  where

import Control.Monad.State.Strict
import Data.Monoid.Reducer

instance Monoid m => Monoid (State s m) where
    mempty = return mempty
    mappend = liftM2 mappend

instance (Monad m, Monoid n) => Monoid (StateT s m n) where
    mempty = return mempty
    mappend = liftM2 mappend

instance Monoid m => Reducer m (State s m) where
    unit = return

instance (Monad m, Monoid n) => Reducer n (StateT s m n) where
    unit = return

instance (Monad m, Monoid n) => Reducer (m n) (StateT s m n) where
    unit = lift