Hi,
(new here)
2007/3/25, Jacques Carette
Some classes would become even more important: monoid, groupoid, semi-group, loop (semi-group with identity), etc. But all of those are, to the average programmer (and many a mathematician), just as scary as Monad.
Of course, when you get that general, you start having the problem that many types can be made into these structures in more than one way. Even the current Monoid class has that problem, even though it has some ties to a particular application (the Writer monad and stuff similar to it -- as reflected in the 'mappend' and 'mconcat' names). You can have newtype wrappers, but that's at least somewhat annoying :-) I'd like to see these classes in the standard library, but I'm not sure at this point whether they are useful enough to have in the prelude, as long as they're not at least losely to a specific application (Field -> numbers; Monoid -> collecting results; Monad -> imperative computations). - Benja