[Haskell-beginners] How to avoid repeating a type restriction from a data constructor

[Daniel Fischer]

On Wednesday 24 April 2013, 10:35:34, gs wrote:
> Daniel Fischer <daniel.is.fischer <at> googlemail.com> writes:
> > Use a GADT,
> > 
> > {-# LANGUAGE GADTs #-}
> > 
> > data Source x y where
> > 
> >     Source :: Variable v => { bindings :: v [Binding a], var :: v a }
> >     
> >                      -> Source v a
> 
> I tried this, but every place that I remove the restriction Variable v =>
> from something using Source, I get an error No instance for (Variable v) ...

Sounds like you're not pattern-matching on the `Source` constructor.

Can you post some example code?