[GHC] #11503: TypeError woes (incl. pattern match checker)

[GHC]

#11503: TypeError woes (incl. pattern match checker)
-------------------------------------+-------------------------------------
        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings,
                                     |  CustomTypeErrors
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14141            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by dfeuer):

 Simon, I imagine there's a broad reason somewhere for

 {{{
 [G] c ~ fsk, [G] fsk
 }}}

 not to be simplified to

 {{{
 [G] c
 }}}

 Assuming that's the case I suspect maybe we should track known insoluble
 constraints the way we track known-bottoming expressions.
 Since `TypeError ... ~ fsk` and `TypeError ...` is insoluble, we could
 conclude that
 `fsk` is insoluble.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11503#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler