[GHC] #10751: Implement Phase 1 of MonadFail Proposal (MFP)

[GHC]

#10751: Implement Phase 1 of MonadFail Proposal (MFP)
-------------------------------------+-------------------------------------
        Reporter:  hvr               |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:  report-
                                     |  impact
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by quchen):

 Current status:

 - Warnings are issued for missing MonadFail instances. These warnings are
 on by default and can be toggled with a flag.
 - The (->)r Monad doesn't yield the correct error message yet: it displays
 as "m r" in the "missing MonadFail" message.
 - There is a flag to turn on the actual desugaring. It's turned off by
 default, but can be used to get a hard error if something's been
 forgotten.
 - The testsuite has been mostly fixed (not sure whether the failing tests
 are our fault, didn't check it yet)
 - We have lots of WIP commits that aren't very good versioning practice,
 so the actual patch will need to be squashed down to a handful of useful
 ones.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10751#comment:3>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler