[GHC] #12648: Stack overflow when using monad-unlift

[GHC]

#12648: Stack overflow when using monad-unlift
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        Reporter:  nh2               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nh2):

 Aha, I made a simple mistake:

 I wrote  `MonadBaseUnlift m IO` instead of  `MonadBaseUnlift IO m`.

 I assume that's a result of `UndecidableSuperClasses` used at
 https://github.com/fpco/monad-
 unlift/blob/adb7869adccc66247cbb1a6175277802e9c098e1/monad-
 unlift/Control/Monad/Trans/Unlift.hs#L13.

 So, the remainder of this ticket is probably: Can we make GHC tell us what
 the problem here is (e.g. with a message like `Gave up trying to resolve
 ... something something` instead of the crash)?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12648#comment:1>
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