#11621: GHC doesn't see () as a Constraint in type family -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.1 checker) | Keywords: Resolution: | ConstraintKinds Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #11715, #13742 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * related: #11715 => #11715, #13742 Comment: Astoundingly, this program appears to have fixed itself between GHC 8.4 and 8.6, since this program: {{{#!hs {-# LANGUAGE DataKinds, TypeOperators, KindSignatures, MultiParamTypeClasses, TypeFamilies #-} import GHC.Exts class NotFound type family F b where F 'False = NotFound F 'True = () }}} Typechecks without issue on GHC 8.6.2 and HEAD. Should we go ahead and add a test case for this, or is this program fragile without a full fix for #11715? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11621#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler