Re: [Haskell-cafe] Type system trickery

Niklas Broberg wrote:

That's what GADTs are for:

data Flag = HasZoo | NoZoo

data Foobar a where Foo :: Foobar a -> Foobar a Bar :: Foobar a -> Foobar a Zoo :: Foobar a -> Foobar HasZoo

Ouch #1: This appears to instantly disable deriving the Eq, Ord and Show instances I want. :-/