Re: [Haskell-cafe] Typeclass question

On Sat, Dec 27, 2008 at 12:44 PM, David Menendez wrote:

On Sat, Dec 27, 2008 at 2:24 PM, Andrew Wagner 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