Re: [GHC] #15355: Functional dependencies can get GHC to print "UnkSkol"

12 Jul 2018

      #15355: Functional dependencies can get GHC to print "UnkSkol"
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        Reporter:  goldfire          |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
                                     |  FunctionalDependencies
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Re (1), see Trac #12466 for a long discussion, and `Note [Given errors]`
 in `TcErrors`.  Bottom line, we suppress some Given errors, which
 represent unreachable code, as here.

 Re (2) HEAD seems better
 {{{
 T15355.hs:12:8: error:
     * Couldn't match type `Double' with `Bool'
         arising from a functional dependency between constraints:
           `C Int _a' arising from a use of `foo' at T15355.hs:12:8-10
           `C Int Double'
             arising from the type signature for:
                            blah :: forall _a. C Int Double => Int -> _a
             at T15355.hs:11:1-33
     * In the expression: foo
       In an equation for `blah': blah = foo
    |
 12 | blah = foo

    |        ^^^
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15355#comment:1
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