#9588: Add `MonadPlus (Either e)` and `Alternative (Either e)` instances -------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Core Libraries | Version: Resolution: | Keywords: report- | impact Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #10755 | Differential Revisions: -------------------------------------+------------------------------------- Description changed by ekmett: Old description:
The following 2 instances are currently Orphans in `transformers` but shall be defined in `base` instead:
{{{#!hs instance MonadPlus (Either e) instance Alterantive (Either e) }}}
This proposal by SPJ already passed the CLC back in April and only needs implementing. I'll submit a patch shortly to Phab
New description: The following 2 instances are currently Orphans in `transformers` but could be defined in `base` without instead: {{{#!hs instance Error e => MonadPlus (Either e) instance Error e => Alterantive (Either e) }}} This would, however, require us to move `Error` from `transformers` into base, which may be a controversial move. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9588#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler