[Haskell-beginners] Re: Classes in Polymorphic Constructors

[John Smith]

On 23/08/2010 18:32, Ertugrul Soeylemez wrote:
> John Smith<voldermort at hotmail.com>  wrote:
>
>> Why can polymorphic data constructors not be instantiated as a class?
>> (not sure if I used the right terminology there)
>>
>> For example,
>>
>> a = [1,True]::[Show]
>> b = "foo":a
>> c = map show b
>>
>> This would obviate the need for wrapper types
>
> Your type signature doesn't make sense.  You are confusing type classes
> with types.  Show is a type class.

My question was why doesn't the type system allow classes to be used in this way. It's the equivalent of a base class or 
interface in OO.