2008/1/21 Alexander Seliverstov <seliverstov.a@gmail.com>:

So, the function type "(Num a)=>Integer->a" means that return value of this function can be cast to any particular instance of class Num.

Ok. I have a my own class "class A a" and want to write function like this  "f:: (A a)=>Integer->a". Can I do it?

Only if you make the function f a member of class A.  Then it is the responsibility of each particular type which is an instance of A to define a way of converting an Integer into a value of that type.  For example:

class A a where
  f :: Integer -> a
  ... other functions...

instance A Integer where
  f = id

instance A String where
  f = show

and so on.

-Brent