Scoped type variables

[Ashley Yakeley]

Ben Rudiak-Gould wrote:
> Simon PJ thinks that Haskell' should include scoped type variables, and 
> I tend to agree. But I'm unhappy with one aspect of the way they're 
> implemented in GHC. What I don't like is that given a signature like
> 
>     x :: a -> a
> 
> there's no way to tell, looking at it in isolation, whether a is free or 
> bound in the type.

I'd quite like to see a flag that switches off implicit "forall" 
quantification altogether, or maybe just warned about it (since I use 
-Wall -Werror anyway).

   id :: forall a. a -> a
   const :: forall a b. a -> b -> a

etc.