[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
           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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 I found that with the following simple program I could make runghc/ghci
 crash with `*** Exception: stack overflow`:

 {{{
 #!/usr/bin/env stack
 -- stack --resolver lts-7.1 --install-ghc runghc --package monad-
 unlift-0.2.0

 {-# LANGUAGE FlexibleContexts #-}

 import Control.Monad.Trans.Unlift

 f :: (MonadBaseUnlift m IO) => m a
 f = do

  _ <- askUnliftBase

  return ()
 }}}

 I'm not super sure if that's OK. Probably not; even if it does trigger an
 undecideable case, shouldn't ghc tell me about it instead of just
 crashing?

 The `monad-unlift` code used is here: https://github.com/fpco/monad-
 unlift/blob/adb7869adccc66247cbb1a6175277802e9c098e1/monad-
 unlift/Control/Monad/Trans/Unlift.hs

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12648>
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