Hello,
playing with GADTs I ran into a problem with rigid type variables
which is ilustrated by the following example. I think it should be
pretty clear what I'am trying to express... Any suggestions?
snip
{-# LANGUAGE GADTs #-}
data Foo where
Foo :: (Eq t) = t - Foo
instance Eq Foo
The problem is that you have an existential `t` there, and two values of the
type Foo might not have the same `t` inside them.
What do you want to happen if someone writes Foo True == Foo yep?
The only real solution here is to parametrize your Foo type by the t that
lives within it, so you can
On Sun, Aug 22, 2010 at 7:47 PM, Daniel Peebles pumpkin...@gmail.com wrote:
You could also do some (in my opinion) fairly nasty stuff with
Dynamic or Typeable, adding a constraint to the Eq and
attempting to cast at runtime (returning False if the cast
returns Nothing).
This is what he's
