Looks like a definite bug. Filed as #10977 https://ghc.haskell.org/trac/ghc/ticket/10997
Matt On Wed, Oct 21, 2015 at 12:49 PM, Sreenidhi Nair <[email protected]> wrote: > Hello, > > We have a pattern synonym as follows > > type family Showable (a :: k) :: Constraint where > Showable (a :: *) = (Show a) > Showable a = () > > pattern Just' :: () => (Showable a) => a -> (Maybe a) > pattern Just' a <- (extractJust -> (True, a)) where > Just' a = Just a > > When we try to use the pattern in a different package, the error was > > [1 of 1] Compiling Bar ( Bar.hs, > .stack-work/dist/x86_64-linux/Cabal-1.22.4.0/build/Bar.o ) > > /tmp/test/p2/.stack-work/install/x86_64-linux/lts-3.5/7.10.2/lib/x86_64-linux-ghc-7.10.2/p1-0.1.0.0-I5t4il6dN7vIqsT1XgYsM3/Foo.hi > Declaration for Just' > Pattern synonym Just': > Iface type variable out of scope: k > Cannot continue after interface file error > > The error only occurred when Showable was polykinded and we used synonym in > a different package . Using the synonym in the same package works fine. > > This problem did not happen with the following definition of (non polykinded > ) Showable > > type family Showable a :: Constraint where > Showable a = (Show a) > > We have attached the sample packages which simulate the exact scenario > described above. > > -- > Yours truly, > Sreenidhi Nair > > _______________________________________________ > ghc-devs mailing list > [email protected] > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
