[GHC] #14249: ApplicativeDo: Pattern matching on a bind forces a Monad constraint

[GHC]

#14249: ApplicativeDo: Pattern matching on a bind forces a Monad constraint
-------------------------------+--------------------------------------
        Reporter:  mutantmell  |                Owner:  (none)
            Type:  bug         |               Status:  closed
        Priority:  normal      |            Milestone:
       Component:  Compiler    |              Version:  8.2.1
      Resolution:  invalid     |             Keywords:  ApplicativeDo
Operating System:  Linux       |         Architecture:  x86_64 (amd64)
 Type of failure:  Other       |            Test Case:
      Blocked By:              |             Blocking:
 Related Tickets:              |  Differential Rev(s):
       Wiki Page:              |
-------------------------------+--------------------------------------

Comment (by mutantmell):

 I was updating a codebase to 8.2 when I ran into this -- the only thing
 ghc told me was that my previously valid signature was wrong. Having the
 compiler output extra information here similar to how it informs the user
 about Language Extensions would have helped.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14249#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler