#12082: Typeable on RealWorld fails -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: merge Priority: high | Milestone: 8.0.2 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Typeable Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: | typecheck/should_run/TypeRep Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2240, Wiki Page: | Phab:D2239 -------------------------------------+------------------------------------- Comment (by acfoltzer): We've somehow managed to run into this without using `typeRep` directly. Here is a shrink: {{{#!hs {-# LANGUAGE Rank2Types #-} import Data.Typeable (Typeable) import Control.Monad.ST (RealWorld) f :: forall a. (forall b. Typeable b => b -> a) -> a f = undefined :: (RealWorld -> a) -> a }}} {{{ % ghci Crash.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from ... [1 of 1] Compiling Main ( Crash.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-apple-darwin): tyConRep RealWorld Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Leaving GHCi. }}} We were able to get around it for our project (it turned out we didn't need to use `RealWorld` at all) but hopefully this test case helps validate the patch for this issue. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12082#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler