Control.Monad.Error

Control.Monad.Error

Portability	non-portable (reqruires multi-param type classes)
Stability	experimental
Maintainer	libraries@haskell.org

Description

The Error monad.

Rendered by Michael Weber mailto:michael.weber@post.rwth-aachen.de, inspired by the Haskell Monad Template Library from Andy Gill (http://www.cse.ogi.edu/~andy)

class Error a where

Methods

strMsg :: String -> a

noMsg :: a

Instances

class (Monad m) => MonadError e m | m -> e where

Methods

catchError :: m a -> (e -> m a) -> m a

throwError :: e -> m a

Instances

MonadError IOError IO

(Error e) => MonadError e (Either e)

(Monad m, Error e) => MonadError e (ErrorT e m)

(MonadError e m) => MonadError e (ReaderT r m)

(Monoid w, MonadError e m) => MonadError e (WriterT w m)

(MonadError e m) => MonadError e (StateT s m)

(Monoid w, MonadError e m) => MonadError e (RWST r w s m)

(MonadError e m) => MonadError e (ListT m)

data ErrorT e m a

Constructors

ErrorT

runErrorT :: (m (Either e a))

Instances

(Monad m) => Functor (ErrorT e m)

(Monad m, Error e) => Monad (ErrorT e m)

(Monad m, Error e) => MonadPlus (ErrorT e m)

(MonadFix m, Error e) => MonadFix (ErrorT e m)

(Monad m, Error e) => MonadError e (ErrorT e m)

(Error e) => MonadTrans (ErrorT e)

(Error e, MonadIO m) => MonadIO (ErrorT e m)

(Error e, MonadReader r m) => MonadReader r (ErrorT e m)

(Error e, MonadWriter w m) => MonadWriter w (ErrorT e m)

(Error e, MonadState s m) => MonadState s (ErrorT e m)

(Error e, MonadCont m) => MonadCont (ErrorT e m)

runErrorT :: ErrorT e m a -> m (Either e a)

mapErrorT :: (m (Either e a) -> n (Either e' b)) -> ErrorT e m a -> ErrorT e' n b

module Control.Monad

module Control.Monad.Fix

module Control.Monad.Trans

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