Excerpts from Eric Seidel's message of 2015-09-04 08:29:59 -0700: > You mention NFData in the motivation but then say that !Maybe !Int is > not allowed. This leads me to wonder what the semantics of > > foo :: !Maybe Int -> !Maybe Int > foo x = x > > bar = foo (Just undefined) > > are. Based on the FAQ it sounds like foo would *not* force the > undefined, is that correct?
Yes. So maybe NFData is a *bad* example! > Also, there's a clear connection between these UnliftedTypes and > BangPatterns, but as I understand it the ! is essentially a new type > constructor. So while > > foo1 :: !Int -> !Int > foo1 x = x > > and > > foo2 :: Int -> Int > foo2 !x = x > > have the same runtime behavior, they have different types, so you can't > pass a regular Int to foo1. Is that desirable? Yes. Actually, you have a good point that we'd like to have functions 'force :: Int -> !Int' and 'suspend :: !Int -> Int'. Unfortunately, we can't generate 'Coercible' instances for these types unless Coercible becomes polykinded. Perhaps we can make a new type class, or just magic polymorphic functions. Edward _______________________________________________ ghc-devs mailing list [email protected] http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs
