[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:  new
        Priority:  normal            |            Milestone:
       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):
       Wiki Page:                    |
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Comment (by goldfire):

 I use `fail` in the `Q` monad and `recover` (in singletons). They are
 useful.

 I think adding a `MonadFail` superclass is the right way to go. User-
 defined instances of `Quasi` are rare. And TH generally undergoes quite a
 bit of churn between releases, so we certainly don't need to worry about
 the 3-release stability policy.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11661#comment:8>
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