[Haskell-cafe] type inference and named fields
jcast at ou.edu
Sun Jun 26 18:40:56 EDT 2005
Lennart Augustsson <lennart at augustsson.net> wrote:
> There are, of course, type systems where my program works fine.
> O'Haskell is an example of a language with such a type system. In
> O'Haskell the Either type is defined like this:
> data Left a = Left a
> data Right a = Right a
> data Either a b > Left a, Right b
> which means that Either is really a union of the Left and Right types.
> Now my program type checks. :)
> foo :: Either a b -> Either () b
> foo (Left _) = Left ()
> foo x@(Right _) = x
> And it has type checked in various type systems for quite a while, but
> not in System F. But System F is not the end all of type systems.
OK. I happily yield.
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