[TYPES] A show-stopping problem for modular type classes?

[Karl Crary]

Brian Hulley wrote:
> For example you say that (a) is an abstract type. But I could argue 
> that (a) is actually a placeholder that represents any particular 
> concrete type, and that the function definition above should be 
> understood as representing a template for an infinite number of 
> monomorphic functions, one of which will accept the argument type (G 
> Int).
>

Evidently you mean something different by "abstract type" than I do.  I 
would say that a placeholder representing any concrete type is precisely 
an abstract type.

    -- Karl