#10997: Pattern synonym causes Iface error. -------------------------------------+------------------------------------- Reporter: mpickering | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mpickering): Yes, see the attached file and run "stack build" in p2/ is one way. Another way to trigger it is to have, two files `Foo.hs` and `Bar.hs` as follows. Then run the following commands.. {{{ ghc Bar.hs vim Bar.hs .... make a simple change... ghc Bar.hs }}} {{{ [2 of 2] Compiling Bar ( Bar.hs, Bar.o ) The interface for ‘Foo’ Declaration for Just' Pattern synonym Just': Iface type variable out of scope: k Cannot continue after interface file error }}} {{{ {-# LANGUAGE PatternSynonyms, ViewPatterns, ConstraintKinds, TypeFamilies, PolyKinds, KindSignatures #-} module Foo where import GHC.Exts type family Showable (a :: k) :: Constraint where Showable (a :: *) = (Show a) Showable a = () extractJust :: Maybe a -> (Bool, a) extractJust (Just a) = (True, a) extractJust _ = (False, undefined) pattern Just' :: () => (Showable a) => a -> (Maybe a) pattern Just' a <- (extractJust -> (True, a)) where Just' a = Just a }}} {{{ module Bar where import Foo bar :: (Showable a) => Maybe a -> Maybe a bar (Just' a) = Just' a }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10997#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler