Am Mittwoch, 31. März 2004 09:32 schrieben Sie:
On Wed, Mar 31, 2004 at 08:48:35AM +0200, Wolfgang Jeltsch wrote:
Now, as i think a little more about it, i believe what you want to do makes no sense. The monad operation '>>=' works on monads over *different* 'element' (i.e. argument) types (look at the type of '>>='). Your implementation only works if argument types are the same. I can't see how this can be generalized to different argument types even if both are instances of class Ord.
I disagree. AFAICS, his implementation also works with different element types. Am I overlooking something?
I think the real issue is that you can't restrict the types on which monad operates without modifying the Monad class.
Exactly. You would be able to define a meaningful Monad instance for Set if Monad would have an Ord restriction on its "element" types. But since Monad doesn't have this restriction, you cannot make a meaningful Monad instance of Set.
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Wolfgang