#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