[GHC] #12466: Typechecker regression: Inaccessible code in a type expected by the context

[GHC]

#12466: Typechecker regression: Inaccessible code in a type expected by the context
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.2.1
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 Replying to [comment:34 simonpj]:
 > I propose (comment:31) to report an error for a Given insoluble (e.g.
 `Int ~ Bool`) only if
 >  * there is an enclosing pattern match
 >  * that binds some equalities
 >
 > Otherwise silently ignore Given insolubles.  That will resolve all the
 complaints here, I think.
 >
 > It's possible that we should warn; but it'd have to be not in `-Wall`
 because in some cases (like the instance one above) you can't "fix" the
 program to avoid the warning.  So for now I'm inclined just to silently
 ignore.
 >
 > OK?  Patch in preparation.
 >
 > Simon

 Can you give an example or two of code that will still produce an error?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12466#comment:35>
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