On Sat, Dec 27, 2008 at 2:24 PM, Andrew Wagner <wagner.andrew@gmail.com> wrote:
> I'm sure there's a way to do this, but it's escaping me at present. I want
> to do something like this:
>
> data Foo = Bar a => Foo a Bool ...
>
> That is, I want to create a new type, Foo, whose constructor takes both a
> Boolean and a value of a type of class Bar.

Try this:

{-# LANGUAGE ExistentialQuantification #-}

data Foo = forall a. Bar a => Foo a Bool

Though for existentials, I find GADT more natural (actually I find GADT more natural in most cases):

data Foo where
Foo :: Bar a => a -> Foo

Luke