#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

#14477: the 'impossible' happened, initTc: unsolved constraints -------------------------------------+------------------------------------- Reporter: bmusin | Owner: (none) Type: bug | Status: closed Priority: high | Milestone: Component: Compiler | Version: 8.0.2 Resolution: duplicate | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #13106 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => closed * resolution: => duplicate * related: => #13106 Old 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

New description: Compile simple program using stack: stack ghc Main.hs code: {{{#!hs 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: Thanks for the bug report. This is a duplicate of #13106, and has been fixed in GHC 8.2: {{{ $ /opt/ghc/8.2.1/bin/ghci Bug.hs GHCi, version 8.2.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:4:15: error: • Data constructor not in scope: Writer :: (Int, [[Char]]) -> Writer [String] Int • Perhaps you meant one of these: ‘WriterT’ (imported from Control.Monad.Writer.Strict), variable ‘writer’ (imported from Control.Monad.Writer.Strict) | 4 | logNumber x = Writer (x, ["Got number: " ++ show x]) | ^^^^^^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14477#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler