-- Hoogle documentation, generated by Haddock
-- See Hoogle, http://www.haskell.org/hoogle/


-- | Arrow-like / category-like composition for transformers.
--   
--   Arrow-like / category-like composition for transformers.
@package transformers-compose
@version 0.1


-- | This module provides Arrow-like monad composition for transformers. To
--   be more precise, it is <a>Category-like</a>, i.e. the parallels are to
--   <tt>Control.Category.Category</tt>.
--   
--   <i>This version has been adapted from monadLib-compose, to work with
--   the transformers package.</i>
--   
--   <tt>Control.Category.Category</tt> generalises <a>.</a> and <a>id</a>
--   to arrows and categories. One such arrow is <tt>Kleisli</tt>, which
--   represents functions returning monadic values. Incidentally, that's
--   equivalent to <a>ReaderT</a>! So it turns out that it is possible to
--   generalise <a>.</a> and <a>id</a> to <a>ReaderT</a> (<a>id</a> is just
--   <a>ask</a>), as well as to many monad transformer stacks that embed a
--   <a>ReaderT</a> inside.
module Control.Monad.Compose.Class

-- | Composable monads. Compare with <tt>Control.Category.Category</tt>.
--   Note that there are two different monad types involved in each
--   instance.
class (Monad m, Monad n) => MonadCompose m n s t | m -> s, n -> t, n s -> m
mcompose :: MonadCompose m n s t => m a -> n s -> n a
mapply :: MonadCompose m n s t => m a -> s -> n a

-- | Compose two monadic values from right to left. Compare with
--   <tt>Control.Category.&lt;&lt;&lt;</tt>. <tt>f &lt;&lt;&lt; g</tt> is
--   equivalent to <tt>mcompose f g</tt>.
(<<<) :: MonadCompose m n s t => m a -> n s -> n a

-- | Compose two monadic values from left to right. Compare with
--   <tt>Control.Category.&gt;&gt;&gt;</tt>. <tt>g &gt;&gt;&gt; f</tt> is
--   equivalent to <tt>mcompose f g</tt>.
(>>>) :: MonadCompose m n s t => n s -> m a -> n a
instance (Monad m, Monoid w) => MonadCompose (RWST s w i m) (RWST t w i m) s t
instance (Monad m, Monoid w) => MonadCompose (RWST s w i m) (RWST t w i m) s t
instance (MonadCompose m n s t, Monoid w) => MonadCompose (WriterT w m) (WriterT w n) s t
instance (MonadCompose m n s t, Monoid w) => MonadCompose (WriterT w m) (WriterT w n) s t
instance MonadCompose m n s t => MonadCompose (StateT i m) (StateT i n) s t
instance MonadCompose m n s t => MonadCompose (StateT i m) (StateT i n) s t
instance (MonadCompose m n s t, Error e) => MonadCompose (ErrorT e m) (ErrorT e n) s t
instance MonadCompose m n s t => MonadCompose (MaybeT m) (MaybeT n) s t
instance MonadCompose m n s t => MonadCompose (IdentityT m) (IdentityT n) s t
instance Monad m => MonadCompose (ReaderT s m) (ReaderT t m) s t
instance MonadCompose ((->) s) ((->) t) s t