[GHC] #14517: ghc: panic! (the 'impossible' happened)

[GHC]

#14517: ghc: panic! (the 'impossible' happened)
-------------------------------------+-------------------------------------
           Reporter:  KtorZ          |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.2
           Keywords:                 |  Operating System:  Linux
       Architecture:  x86_64         |   Type of failure:  Compile-time
  (amd64)                            |  crash or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 Apparently not so impossible. I am just filling a bug following the advice
 of GHC.

 Here's the error message coming out of GHC

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.2 for x86_64-unknown-linux):
         initTc: unsolved constraints
   WC {wc_insol =
         [W] liftIO_a2jc :: t_a2jb[tau:1] (CHoleCan: liftIO)
         [W] handleMsg_a2k6 :: t_a2k5[tau:1] (CHoleCan: handleMsg)
         [W] expectTimeout_a2kb :: t_a2ka[tau:1] (CHoleCan: expectTimeout)
         [W] sendMsg_a2v9 :: t_a2v8[tau:1] (CHoleCan: sendMsg)
         [W] tick_a2vc :: t_a2vb[tau:1] (CHoleCan: tick)}

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 And here the corresponding code that leads to this compilation error:

 {{{
 module Main where

 import           Control.Distributed.Process (NodeId (..), Process)
 import           Control.Monad               (forever)
 import           Data.IORef                  (IORef, newIORef)


 type Clock =
   Int

 emitRandomNumbers :: [NodeId] -> Process ()
 emitRandomNumbers nodes = do
   clock <-
     liftIO $ newIORef (0 :: Clock)

   forever $ do
     msg <-
       handleMsg <$> expectTimeout 0

     sendMsg <$> tick
 }}}

 I am compiling on with GHC 8.0.2 on Ubuntu 16.04, here are a list of the
 install dependencies:

 {{{
 array 0.5.1.1
 base 4.9.1.0
 binary 0.8.3.0
 bytestring 0.10.8.1
 containers 0.5.7.1
 data-accessor 0.2.2.7
 deepseq 1.4.2.0
 distributed-process 0.7.3
 distributed-static 0.3.8
 exceptions 0.8.3
 getting-started 0.1.0.0
 ghc-boot-th 8.0.2
 ghc-prim 0.5.0.0
 hashable 1.2.6.1
 integer-gmp 1.0.0.1
 mtl 2.2.1
 network 2.6.3.2
 network-transport 0.4.4.0
 network-transport-tcp 0.5.1
 pretty 1.1.3.3
 random 1.1
 rank1dynamic 0.3.3.0
 rts 1.0
 stm 2.4.4.1
 syb 0.7
 template-haskell 2.11.1.0
 text 1.2.2.2
 time 1.6.0.1
 transformers 0.5.2.0
 transformers-compat 0.5.1.4
 unix 2.7.2.1
 }}}

 Let me know should you need any additional informations.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14517>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler