Safe Haskell	Safe-Inferred
Language	Haskell98

Network.Gitit.Compat.Except

Synopsis

Documentation

type ExceptT = ErrorT Source

type Except s a = ErrorT s Identity a Source

class Error a where

An exception to be thrown.

Minimal complete definition: noMsg or strMsg.

Minimal complete definition

Nothing

Methods

noMsg :: a

Creates an exception without a message. The default implementation is strMsg "".

strMsg :: String -> a

Creates an exception with a message. The default implementation of strMsg s is noMsg.

Instances

Error CPError
Error IOException
Error Response
Error PandocError
ErrorList a => Error [a]	A string can be thrown as an error.
Error (Errors String)

runExceptT :: ExceptT e m a -> m (Either e a) Source

runExcept :: ExceptT e Identity a -> Either e a Source

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

The strategy of combining computations that can throw exceptions by bypassing bound functions from the point an exception is thrown to the point that it is handled.

Is parameterized over the type of error information and the monad type constructor. It is common to use Either String as the monad type constructor for an error monad in which error descriptions take the form of strings. In that case and many other common cases the resulting monad is already defined as an instance of the MonadError class. You can also define your own error type and/or use a monad type constructor other than Either String or Either IOError. In these cases you will have to explicitly define instances of the Error and/or MonadError classes.

Methods

throwError :: e -> m a

Is used within a monadic computation to begin exception processing.

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

A handler function to handle previous errors and return to normal execution. A common idiom is:

do { action1; action2; action3 } `catchError` handler

where the action functions can call throwError. Note that handler and the do-block must have the same return type.

Instances

MonadError IOException IO
MonadError e m => MonadError e (ResourceT m)
MonadError e m => MonadError e (WebT m)
(Monad m, MonadError e m) => MonadError e (ServerPartT m)
MonadError e m => MonadError e (MaybeT m)
MonadError e m => MonadError e (ListT m)
MonadError e m => MonadError e (IdentityT m)
MonadError e (Either e)
Monad m => MonadError e (ExceptT e m)
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
MonadError e m => MonadError e (StateT s m)
MonadError e m => MonadError e (StateT s m)
MonadError e m => MonadError e (ReaderT r m)
(Monad m, Error e) => MonadError e (ErrorT e m)
MonadError e m => MonadError e (ParsecT s u m)
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)
(Monoid w, MonadError e m) => MonadError e (RWST r w s m)

throwError :: MonadError e m => forall a. e -> m a

Is used within a monadic computation to begin exception processing.

catchError :: MonadError e m => forall a. m a -> (e -> m a) -> m a

A handler function to handle previous errors and return to normal execution. A common idiom is:

do { action1; action2; action3 } `catchError` handler

where the action functions can call throwError. Note that handler and the do-block must have the same return type.