Copyright	(c) 2016 Allele Dev; 2017 Ixperta Solutions s.r.o.; 2017 Alexis King
License	BSD3
Maintainer	Alexis King <lexi.lambda@gmail.com>
Stability	experimental
Portability	GHC specific language extensions.
Safe Haskell	None
Language	Haskell2010

Control.Monad.Freer.Error

Description

Composable handler for Error effects. Communicates success/failure via an Either type.

Using http://okmij.org/ftp/Haskell/extensible/Eff1.hs as a starting point.

Synopsis

newtype Error e r where
- Error :: e -> Error e r
throwError :: forall e effs a. Member (Error e) effs => e -> Eff effs a
runError :: forall e effs a. Eff (Error e ': effs) a -> Eff effs (Either e a)
catchError :: forall e effs a. Member (Error e) effs => Eff effs a -> (e -> Eff effs a) -> Eff effs a
handleError :: forall e effs a. Eff (Error e ': effs) a -> (e -> Eff effs a) -> Eff effs a

Documentation

newtype Error e r where Source #

Exceptions of the type e :: * with no resumption.

Constructors

Error :: e -> Error e r

throwError :: forall e effs a. Member (Error e) effs => e -> Eff effs a Source #

Throws an error carrying information of type e :: *.

runError :: forall e effs a. Eff (Error e ': effs) a -> Eff effs (Either e a) Source #

Handler for exception effects. If there are no exceptions thrown, returns Right. If exceptions are thrown and not handled, returns Left, while interrupting the execution of any other effect handlers.

catchError :: forall e effs a. Member (Error e) effs => Eff effs a -> (e -> Eff effs a) -> Eff effs a Source #

A catcher for Exceptions. Handlers are allowed to rethrow exceptions.

handleError :: forall e effs a. Eff (Error e ': effs) a -> (e -> Eff effs a) -> Eff effs a Source #

A catcher for Exceptions. Handlers are not allowed to rethrow exceptions.