[GHC] #11661: Missing MonadFail instance for Q monad from TemplateHaskell

[GHC]

#11661: Missing MonadFail instance for Q monad from TemplateHaskell
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        Reporter:  PeterTrsko        |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Template Haskell  |              Version:  8.0.1-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  phab:D1982
       Wiki Page:                    |
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"1c76e1686bd4291556ae9357151f256c805b4b5d/ghc" 1c76e16/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1c76e1686bd4291556ae9357151f256c805b4b5d"
 template-haskell: define `MonadFail Q` instance

 When `MonadFail`is available, this patch makes `MonadFail` a superclass
 of `Quasi`, and `Q` an instance of `MonadFail`.

 NB: Since f16ddcee0c64a92ab911a7841a8cf64e3ac671fd, we need to be able
     to compile `template-haskell` with stage0 compilers that don't provide
     a `MonadFail` class yet. Once we reach GHC 8.3 development we can drop
     the CPP conditionals again.

 Addresses #11661

 Reviewed By: bgamari, goldfire

 Differential Revision: https://phabricator.haskell.org/D1982
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11661#comment:10>
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