[GHC] #10642: Coercible regression from 7.10 to HEAD

[GHC]

#10642: Coercible regression from 7.10 to HEAD
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        Reporter:  darchon           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.11
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by darchon):

 The example can be even further simplified to:

 {{{
 {-# LANGUAGE TypeFamilies #-}
 module CoerceFail where

 import Data.Coerce

 type family F a

 newtype D a = D (F a)

 -- | This works on 7.10.1, but fails on HEAD (20150711)
 coerceD :: F a -> D a
 coerceD = coerce
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10642#comment:1>
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