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

[Daniel Fischer]

On Wednesday 24 April 2013, 12:27:23, gs wrote:
> Daniel Fischer <daniel.is.fischer <at> googlemail.com> writes:
> > 
> > Can you post some example code?
> 
> http://code.accursoft.com/binding/src/c13ccbbec0ba8e326369ff2252863f20a891ef
> 76/binding-core/src/Data/Binding/Simple.hs
> 
> http://code.accursoft.com/binding/src/c13ccbbec0ba8e326369ff2252863f20a891ef
> 76/binding-core/src/Data/Binding/List.hs

I meant example code using a GADT for Source, and not DatatypeContexts; and 
some function where you still need the context.