[Haskell-cafe] Re: Type question in instance of a class

Peter Hercek phercek at gmail.com
Sun Nov 16 19:06:08 EST 2008


Bulat Ziganshin wrote:
> Hello J.,
> 
> Monday, November 17, 2008, 12:56:02 AM, you wrote:
> 
>>> class MyClass r where function :: r -> s
>> As Bulat said, your type signature is equivalent to:
> 
>> function :: forall r s. r -> s
> 
> only
> 
> function :: forall s. r -> s
> 
> (r is fixed in class header)
> 

... and the only value the function can return is bottom.
Is there any type system which would have more than
  one value which inhabits all types?

Peter.



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