[GHC] #11276: GHC hangs/takes an exponential amount of time with simple program

[GHC]

#11276: GHC hangs/takes an exponential amount of time with simple program
-------------------------------------+-------------------------------------
        Reporter:  mpickering        |                Owner:  gkaracha
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by gkaracha):

 Hmmm, the problem appears only with data families right now I think.
 Dropping the wrapper in the general case does not help because we end up
 with non-satisfiable constraints. We could deactivate pm checking for
 matches that contain `CoPat`s but this goes beyond data families (as the
 original test case without the signature has shown). I am still trying
 some ideas but I do not know exactly how much time will I need or if they
 are going to work after all. What is the time frame?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11276#comment:13>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler