#13585: ala from Control.Lens.Wrapped panics -------------------------------------+------------------------------------- Reporter: fumieval | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: checker) | Resolution: | Keywords: Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by fumieval: @@ -46,0 +46,3 @@ + + Control.Lens.Wrapped is from the latest version of lens on GitHub: + https://github.com/ekmett/lens/blob/9c4447de7ef57f67dbe293320d45bd8a546be522... New description: Panic.hs: {{{ module Panic where import Control.Lens.Wrapped import Data.Monoid foo :: Maybe String foo = ala Last foldMap [Just "foo"] }}} main.hs: {{{ module Main where import Panic (foo) main :: IO () main = print foo }}} {{{ $ ghc -c -O2 Panic.hs $ ghc -c -O2 main.hs ghc: panic! (the 'impossible' happened) (GHC version 8.2.0.20170404 for x86_64-unknown-linux): splitTyConApp (Exchange (Unwrapped (Last String)) (Unwrapped (Last String)) |> <* -> * -> *>_N) (Maybe [Char]) ((Identity |> <* -> *>_N) (Maybe [Char])) Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1134:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1138:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:1105:34 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} The GHC version is 8134f7d4ba2c14b2f24d2f4c1f5260fcaff3304a. Control.Lens.Wrapped is from the latest version of lens on GitHub: https://github.com/ekmett/lens/blob/9c4447de7ef57f67dbe293320d45bd8a546be522... -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13585#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler