On Wednesday 31 March 2004 08:48, Wolfgang Jeltsch wrote:
Am Mittwoch, 31. März 2004 03:11 schrieb Benjamin Franksen:
instance Monad Set where m >>= k = concatSets (mapSet k m) return x = unitSet x fail s = emptySet
concatSets sets = foldl union emptySet (setToList sets) instance (Eq b,Ord b) => Ord (Set b) where compare set1 set2 = compare (setToList set1) (setToList set2)> [...]
[...]
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?
No, you are right. I failed to notice the call to mapSet. Sorry for the confusion. Ben