Somehow I didn't receive David's mail, but his explanation makes a lot
of sense. I'm still wondering how this results in a type error involving
rigid type variables.
Ryan Ingram wrote:
On Fri, Aug 14, 2009 at 12:03 PM, Dan Weston<weston...@imageworks.com> wrote:
But presumably he can use a data family instead of a type family to restore
injectivity, at the cost of adding an extra wrapped bottom value and one
more layer of value constructor?
Actually, you don't even necessarily pay this penalty, since you can
put newtypes into data families.
data family Foo a
newtype instance Foo () = UnitFoo Int
You do need to add the constructor wrap/unwrapping in code, but they
all get erased after typechecking.
-- ryan
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
