[Haskell-cafe] confusion about 'instance'....

Tillmann Rendel rendel at rbg.informatik.tu-darmstadt.de
Thu Jan 10 10:45:00 EST 2008

Nicholls, Mark wrote:

> I only have 1 type.
> If I say "my name is mark" twice, it doesn't mean I belong to set of
> objects called Mark twice.... 

Typeclasses define not only sets of types, but a common interface for 
these types, too. An analogy would be to say:

   I have a name, and it is Marc.
   I have a name, and it is John.

 From a "set of things" perspective, there is no problem: you belong to 
the set of people having a name. But what name should I actually use 
when I want to adress you?


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