{-# LANGUAGE UndecidableInstances #-} -- Search for UndecidableInstances to see why this is needed ----------------------------------------------------------------------------- -- | -- Module : Control.Monad.RWS.Class -- Copyright : (c) Andy Gill 2001, -- (c) Oregon Graduate Institute of Science and Technology, 2001 -- License : BSD-style (see the file libraries/base/LICENSE) -- -- Maintainer : libraries@haskell.org -- Stability : experimental -- Portability : non-portable (multi-param classes, functional dependencies) -- -- Declaration of the MonadRWS class. -- -- 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.RWS.Class ( MonadRWS, module Control.Monad.Reader.Class, module Control.Monad.State.Class, module Control.Monad.Writer.Class, ) where import Control.Monad.Reader.Class import Control.Monad.State.Class import Control.Monad.Writer.Class import Control.Monad.Trans.Error(Error, ErrorT) import Control.Monad.Trans.RWS.Lazy as Lazy (RWST) import qualified Control.Monad.Trans.RWS.Strict as Strict (RWST) import Data.Monoid class (Monoid w, MonadReader r m, MonadWriter w m, MonadState s m) => MonadRWS r w s m | m -> r, m -> w, m -> s instance (Monoid w, Monad m) => MonadRWS r w s (Lazy.RWST r w s m) instance (Monoid w, Monad m) => MonadRWS r w s (Strict.RWST r w s m) --------------------------------------------------------------------------- -- Instances for other mtl transformers -- This instance needs UndecidableInstances, because -- it does not satisfy the coverage condition instance (Error e, MonadRWS r w s m) => MonadRWS r w s (ErrorT e m)