[Haskell-beginners] Question about List Type Constraint and Null

[Jürgen Doser]

El sáb, 22-01-2011 a las 00:03 -0600, aditya siram escribió:
>
> But I have a further question why should 'null ...' care about the
> type of its list argument? Isn't it polymorphic?  So it shouldn't make
> a difference that the 'a' inside res is ambiguous because we know for
> sure that it always returns a list of some kind.

The point is that for different types for res, the list has a different
number of elements. So without saying what the type of res is, you
cannot know if the list is empty or not.

	Jürgen