#9588: Add `MonadPlus {IO,Either e}` and `Alternative (Either e)` instances -------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: 7.10.1 Component: | Version: libraries/base | Keywords: Resolution: | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: | Related Tickets: None/Unknown | Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by ekmett): The `IO` case is easy and should definitely go in. That one is a no- brainer. However, looking at it, I'm rather uncomfortable about the notion of moving the rather ad hoc `Error` class into `base`. Nobody likes it. Perhaps the fate of the `Either` instance should go back out to the libraries mailing list to try to round up ideas. We could a.) Leave it where it is b.) Bring `Error` into base. c.) Switch it to `Monoid`, which is sadly too big and may break some usecases where `noMsg /= mempty` holds now. d.) Bring `Default` into base, which IIRC was already rejected by the `libraries@` list, and use that instead. e.) Figure out something else. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9588#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler