#14477: the 'impossible' happened, initTc: unsolved constraints ---------------------------------+-------------------------------------- Reporter: bmusin | Owner: (none) Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 (amd64) Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | ---------------------------------+-------------------------------------- Old description: New description: Compile simple program using stack: stack ghc Main.hs code: import Control.Monad.Writer.Strict logNumber :: Int -> Writer [String] Int logNumber x = Writer (x, ["Got number: " ++ show x]) multWithLog :: Writer [String] Int multWithLog = do a <- logNumber 3 b <- logNumber 5 tell ["Gonnay multiply these two"] return (a*b) [1 of 1] Compiling Main ( Main.hs, Main.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-linux): initTc: unsolved constraints WC {wc_insol = [W] Writer_a19y :: t_a19x[tau:1] (CHoleCan: Writer)} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug -- Comment (by bmusin): Completed ticked description, initially submitted incomplete bug by mistake. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14477#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler