Instance checking and phantom types

[Sven Panne]

Nick Name wrote:
> Got it ;) Thanks for prompt reply. What does "should always be explicit" 
> mean? Is there a notion of "explicit context" that I should know?

What I meant was the fact that you always have to write down *all* contexts
involved in a type signature. Nothing is "inherited under the hood" by
contexts in datatype declarations.

Cheers,
    S.