Hi Larry, On 11/11/2014 09:59 PM, Larry Lee wrote:
Hi
I have a very simple problem. I have a class and want to define a function in that class that returns a different instance of the same class.
I tried accomplishing this as follows:
class A a where f :: A b => a -> b
This fails however when I try to instantiate it. For example:
instance A String where f x = x
I get an error message that makes absolutely no sense to me:
f has type (A a, A b) => a -> b. Both a and b can be thosen by the caller. If you try to create an instance of A like you did, this will not type check, as you have only provided a function of type String -> String, whereas a function of type A b => String -> b (for *all* b) is required. I hope that clears things up a little. Thanks, Jochem -- Jochem Berndsen | jochem@functor.nl