Hi Jason,

On Tuesday 19 May 2009 19:17:56 Jason Dagit wrote:
> >> I have not made a typeclass for test results, because that would make it
> >> impossible to put test results of mixed origin in a list.
>
> I don't understand this comment.  Makes it impossible unless someone
> writes an instance for the particular datatype?
>
> Lists can be created like this, Foo a => [a], so I don't really see
> what the problem is without further investigation (see below).

I don't see much below so I'll reply here. AFAIK lists always require that the 
elements have the same type. Like "data List a = Nil | Cons a (List a)". I 
suppose there can be only one instantiation for a in that GADT definition. And 
all my attempts to create mixed-type lists of Show instances fail in ghci.

Reinier
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