#8553: ASSERT failed compiler/typecheck/TcMType.lhs line 809 -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.6.3 checker) | Operating System: Unknown/Multiple Keywords: | Type of failure: Compile-time Architecture: Unknown/Multiple | crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- With current master (9c2dade94fae5f4fe19cd972ca1f1049c633e4ed) I get {{{ [1 of 1] Compiling ShouldCompile ( ../ghc/gadt6.hs, ../ghc/gadt6.o ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 7.7.20131121 for x86_64-unknown-linux): ASSERT failed! file compiler/typecheck/TcMType.lhs line 809 [W] cobox_aBx{v} [lid] :: t_aBv{tv} [tau[0]] ghc-prim:GHC.Types.~{(w) tc 31Q} t_aBu{tv} [tau[0]] (CIrredEvCan) }}} (And it took me a while to figure out that it was not my code that was introducing the bug.) According to `git log -L 809,809:compiler/typecheck/TcMType.lhs` (a useful feature) the history of the ASSERT is: * SPJ, “Accommodate Derived constraints in two places”, Sep 17, 8cfbdccb7f8716c2b6b13b3c7884f52b1087d782 * SPJ, “Fix an ASSERT”, Oct 1 2012, adb6bcb7b85410dd42828a4824962ce9c6e9d667 * SPJ, “Tidy up and simplify TcMType.zonkFlats”, Sep 17, 2012, bd6b183e092fc7667fc55b3aa15d857f257ec73f -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8553 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler