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


-- | Type classes and monads for unchecked extensible exceptions.
--   
--   This package provides type classes, a monad and a monad transformer
--   that support unchecked extensible exceptions as well as asynchronous
--   exceptions. It is compatible with the transformers package.
@package exception-transformers
@version 0.2


module Control.Monad.Exception

-- | Any type that you wish to throw or catch as an exception must be an
--   instance of the <tt>Exception</tt> class. The simplest case is a new
--   exception type directly below the root:
--   
--   <pre>
--   data MyException = ThisException | ThatException
--       deriving (Show, Typeable)
--   
--   instance Exception MyException
--   </pre>
--   
--   The default method definitions in the <tt>Exception</tt> class do what
--   we need in this case. You can now throw and catch
--   <tt>ThisException</tt> and <tt>ThatException</tt> as exceptions:
--   
--   <pre>
--   *Main&gt; throw ThisException <tt>catch</tt> e -&gt; putStrLn ("Caught " ++ show (e :: MyException))
--   Caught ThisException
--   </pre>
--   
--   In more complicated examples, you may wish to define a whole hierarchy
--   of exceptions:
--   
--   <pre>
--   ---------------------------------------------------------------------
--   -- Make the root exception type for all the exceptions in a compiler
--   
--   data SomeCompilerException = forall e . Exception e =&gt; SomeCompilerException e
--       deriving Typeable
--   
--   instance Show SomeCompilerException where
--       show (SomeCompilerException e) = show e
--   
--   instance Exception SomeCompilerException
--   
--   compilerExceptionToException :: Exception e =&gt; e -&gt; SomeException
--   compilerExceptionToException = toException . SomeCompilerException
--   
--   compilerExceptionFromException :: Exception e =&gt; SomeException -&gt; Maybe e
--   compilerExceptionFromException x = do
--       SomeCompilerException a &lt;- fromException x
--       cast a
--   
--   ---------------------------------------------------------------------
--   -- Make a subhierarchy for exceptions in the frontend of the compiler
--   
--   data SomeFrontendException = forall e . Exception e =&gt; SomeFrontendException e
--       deriving Typeable
--   
--   instance Show SomeFrontendException where
--       show (SomeFrontendException e) = show e
--   
--   instance Exception SomeFrontendException where
--       toException = compilerExceptionToException
--       fromException = compilerExceptionFromException
--   
--   frontendExceptionToException :: Exception e =&gt; e -&gt; SomeException
--   frontendExceptionToException = toException . SomeFrontendException
--   
--   frontendExceptionFromException :: Exception e =&gt; SomeException -&gt; Maybe e
--   frontendExceptionFromException x = do
--       SomeFrontendException a &lt;- fromException x
--       cast a
--   
--   ---------------------------------------------------------------------
--   -- Make an exception type for a particular frontend compiler exception
--   
--   data MismatchedParentheses = MismatchedParentheses
--       deriving (Typeable, Show)
--   
--   instance Exception MismatchedParentheses where
--       toException   = frontendExceptionToException
--       fromException = frontendExceptionFromException
--   </pre>
--   
--   We can now catch a <tt>MismatchedParentheses</tt> exception as
--   <tt>MismatchedParentheses</tt>, <tt>SomeFrontendException</tt> or
--   <tt>SomeCompilerException</tt>, but not other types, e.g.
--   <tt>IOException</tt>:
--   
--   <pre>
--   *Main&gt; throw MismatchedParentheses <tt>catch</tt> e -&gt; putStrLn ("Caught " ++ show (e :: MismatchedParentheses))
--   Caught MismatchedParentheses
--   *Main&gt; throw MismatchedParentheses <tt>catch</tt> e -&gt; putStrLn ("Caught " ++ show (e :: SomeFrontendException))
--   Caught MismatchedParentheses
--   *Main&gt; throw MismatchedParentheses <tt>catch</tt> e -&gt; putStrLn ("Caught " ++ show (e :: SomeCompilerException))
--   Caught MismatchedParentheses
--   *Main&gt; throw MismatchedParentheses <tt>catch</tt> e -&gt; putStrLn ("Caught " ++ show (e :: IOException))
--   *** Exception: MismatchedParentheses
--   </pre>
class (Typeable e, Show e) => Exception e
toException :: Exception e => e -> SomeException
fromException :: Exception e => SomeException -> Maybe e

-- | The <tt>SomeException</tt> type is the root of the exception type
--   hierarchy. When an exception of type <tt>e</tt> is thrown, behind the
--   scenes it is encapsulated in a <tt>SomeException</tt>.
data SomeException :: *
class Monad m => MonadException m
throw :: (MonadException m, Exception e) => e -> m a
catch :: (MonadException m, Exception e) => m a -> (e -> m a) -> m a
class (MonadIO m, MonadException m) => MonadAsyncException m
block :: MonadAsyncException m => m a -> m a
unblock :: MonadAsyncException m => m a -> m a
newtype ExceptionT m a
ExceptionT :: m (Either SomeException a) -> ExceptionT m a
runExceptionT :: ExceptionT m a -> m (Either SomeException a)
mapExceptionT :: (m (Either SomeException a) -> n (Either SomeException b)) -> ExceptionT m a -> ExceptionT n b

-- | Lift the result of running a computation in a monad transformed by
--   <a>ExceptionT</a> into another monad that supports exceptions.
liftException :: MonadException m => Either SomeException a -> m a
instance (Monoid w, MonadAsyncException m) => MonadAsyncException (WriterT w m)
instance (Monoid w, MonadAsyncException m) => MonadAsyncException (WriterT w m)
instance MonadAsyncException m => MonadAsyncException (StateT s m)
instance MonadAsyncException m => MonadAsyncException (StateT s m)
instance MonadAsyncException m => MonadAsyncException (ReaderT r m)
instance (Monoid w, MonadAsyncException m) => MonadAsyncException (RWST r w s m)
instance (Monoid w, MonadAsyncException m) => MonadAsyncException (RWST r w s m)
instance (Monoid w, MonadException m) => MonadException (WriterT w m)
instance (Monoid w, MonadException m) => MonadException (WriterT w m)
instance MonadException m => MonadException (StateT s m)
instance MonadException m => MonadException (StateT s m)
instance MonadException m => MonadException (ReaderT r m)
instance (Monoid w, MonadException m) => MonadException (RWST r w s m)
instance (Monoid w, MonadException m) => MonadException (RWST r w s m)
instance MonadException STM
instance MonadAsyncException IO
instance MonadException IO
instance MonadAsyncException m => MonadAsyncException (ExceptionT m)
instance MonadIO m => MonadIO (ExceptionT m)
instance Monad m => MonadException (ExceptionT m)
instance MonadFix m => MonadFix (ExceptionT m)
instance Monad m => MonadPlus (ExceptionT m)
instance Monad m => Monad (ExceptionT m)
instance Monad m => Functor (ExceptionT m)
instance MonadTrans ExceptionT