> > Yes, nuke MonadPlus. For Haskell 2 we can put these things in a
> > wonderful Monad library.
>
> I had thought that too many functions depend on MonadZero/Plus,
> but actually, it's the following:
>
> filterM :: MonadZero m => (a -> m Bool) -> [a] -> m [a]
> guard :: MonadZero m => Bool -> m ()
> mfilter :: MonadZero m => (a -> Bool) -> m a -> m a
> concatM :: MonadPlus m => [m a] -> m a
>
> These would all vanish, along with MonadZero/Plus.
> The Monad library itself doesn't mention MonadZero/Plus, as it happens.
>
> Phil's proposal:
> delete class MonadZero, MonadPlus
> delete filterM, guard, mfilter, concatM
>
> This is ok by me. Does anyone object?
In fact I don't know these functions, but when they were in the
Prelude can they be less important than those in the Monad
library? Why don't we move the classes and functions into a wonderful
Monad library already now for Haskell 98?
And, BTW, the library report defines types for zeroOrMore and
oneOrMore, which both are (MonadPlus m) => m a -> m [a],
but doesn't mention them later.
Christian Sievers
