Proposal: add handleError to mtl

[Erik de Castro Lopo]

Hi all,

I would like to propose the following convenience function (with
implementation) for the mtl library:

    handleError :: MonadError e m => (e -> m a) -> m a -> m a
    handleError = flip catchError

which follows the handle function from Control.Exception.Base:


    handle :: Exception e => (e -> IO a) -> IO a -> IO a

Like the handle function, handleError allows the handling of
exceptions to be expressed in a more natural way, turning:

    catchError
        ( do
             mumble
             something
             mumble
        )
        handler

into:

    handlerError handler $ do
             mumble
             something
             mumble
         


-- 
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/