NewtypeDeriving

This module provides Template Haskell based derivers for typical newtype instances, which the GeneralizedNewtypeDeriving extension refuses to handle.

Here is what it allows you to do:

{-# LANGUAGE UndecidableInstances, TypeFamilies, FlexibleInstances,
             TemplateHaskell, GeneralizedNewtypeDeriving,
             MultiParamTypeClasses #-}

import NewtypeDeriving
import Control.Monad.Base
import Control.Monad.Trans.Control
import Control.Monad.Trans.Class
import Control.Monad.Trans.Either
import Control.Monad.Trans.Maybe
import Control.Monad.Trans.State
import Control.Monad.Trans.Reader
import Control.Monad.Trans.Writer

newtype T m a =
  T (ReaderT Int (StateT Char (WriterT [Int] (EitherT String (MaybeT m)))) a)
  deriving (Functor, Applicative, Monad)

monadTransInstance ''T
monadTransControlInstance ''T
monadBaseTransformerInstance ''T
monadBaseControlTransformerInstance ''T

Documentation

monadTransInstance :: Name -> Q [Dec]

Given a name of a newtype wrapper produce an instance of Control.Monad.Trans.Class.MonadTrans.

monadBaseTransformerInstance :: Name -> Q [Dec]

Given a name of a newtype wrapper produce an instance of Control.Monad.Base.MonadBase, which is specialised for monad transformers.

monadTransControlInstance :: Name -> Q [Dec]

Given a name of a newtype wrapper produce an instance of Control.Monad.Trans.Control.MonadTransControl.

monadBaseControlTransformerInstance :: Name -> Q [Dec]

Given a name of a newtype wrapper produce an instance of Control.Monad.Trans.Control.MonadBaseControl, which is specialised for monad transformers.