#10348: HEAD: `KnownNat` does not imply `Typeable` any more -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: diatchki Type: bug | Status: new Priority: highest | Milestone: 7.12.1 Component: Compiler (Type | Version: 7.11 checker) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Related Tickets: | -------------------------------------+------------------------------------- Comment (by heisenbug): I changed the test case thus: {{{ diff --git a/testsuite/tests/typecheck/should_compile/T10348.hs b/testsuite/tests/typecheck/should_compile/T10348.hs index 213079b..14fc085 100644 --- a/testsuite/tests/typecheck/should_compile/T10348.hs +++ b/testsuite/tests/typecheck/should_compile/T10348.hs @@ -15,8 +15,7 @@ data T t where deriving instance Show (T n) -hey :: (Typeable n, KnownNat n) => T (Foo n) --- SHOULD BE: hey :: KnownNat n => T (Foo n) +hey :: KnownNat n => T (Foo n) hey = T Hey ho :: T (Foo 42) }}} Then this code (I just added a panic for visibility) is triggered: {{{ diff --git a/compiler/typecheck/TcInteract.hs b/compiler/typecheck/TcInteract.hs index 01b0ba1..bf5f237 100644 --- a/compiler/typecheck/TcInteract.hs +++ b/compiler/typecheck/TcInteract.hs @@ -48,6 +48,7 @@ import Pair (Pair(..)) import Unique( hasKey ) import DynFlags import Util +import TypeRep( Type(..) ) {- ********************************************************************** @@ -1852,6 +1853,8 @@ matchTypeableClass clas _k t | Just (f,kt) <- splitAppTy_maybe t = doTyApp f kt | Just _ <- isNumLitTy t = mkSimpEv (EvTypeableTyLit t) | Just _ <- isStrLitTy t = mkSimpEv (EvTypeableTyLit t) + | TyConApp con [] <- _k + , Just tcon <- isPromotedTyCon_maybe con = pprPanic "matchTypeableClass" $ ppr tcon | otherwise = return NoInstance where }}} I guess code must be generated that creates the Typeable hash on the fly (at runtime) by appealing to the KnownNat's method. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10348#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler