{-# OPTIONS 
   -fglasgow-exts
   -fno-warn-orphans
  #-}

{-# LANGUAGE ScopedTypeVariables, UndecidableInstances #-}


-----------------------------------------------------------------------------
-- |
-- Module      :  Control.Monad.StateX
-- Copyright   :  (c) Mark Snyder 2008.
-- License     :  BSD-style
-- Maintainer  :  Mark Snyder, marks@ittc.ku.edu
-- Portability :  non-portable (multi-param classes, functional dependencies)
--
-- State monads.
--
--      This module is inspired by the paper
--      /Functional Programming with Overloading and
--          Higher-Order Polymorphism/,
--        Mark P Jones (<http://web.cecs.pdx.edu/~mpj/>)
--          Advanced School of Functional Programming, 1995.

-----------------------------------------------------------------------------

module Control.Monad.StateX (
  module Control.Monad.StateX.Lazy,

  module Control.Monad.Index
  ) where

import Control.Monad.StateX.Lazy

import Control.Monad.Index

import Control.Monad.Error
import Control.Monad.State
import Control.Monad.Reader
import Control.Monad.Writer

instance (Error e, MonadStateX ix s m) => MonadStateX ix s (ErrorT e m) where
    getx (ixv::ix) = lift $ getx ixv
    putx (ixv::ix) = lift . putx ixv


instance (MonadStateX ix s1 m, Index ix) 
    => MonadStateX ix s1 (StateT s2 m) where
    getx (ixv::ix)  = StateT $ \s -> do
                              n <- getx ixv
                              return (n,s)
    putx (ixv::ix) (v::s1) = StateT $ \s -> do
                              putx ixv v
                              return ((),s)

instance (Index ix, MonadStateX ix s m) => MonadStateX ix s (ReaderT r m) where
  getx (ixv::ix)   = lift $ getx ixv
  putx (ixv::ix) v = lift $ putx ixv v


instance (Index ix, MonadStateX ix s m, Monoid w) => MonadStateX ix s (WriterT w m) where
   getx (ixv::ix)   = lift $ getx ixv
   putx (ixv::ix) s = lift $ putx ixv s