> | class Monad m => MonadPlus m where
> | mzero :: m a
> | mplus :: m a -> m a -> m a
> |
> | Why is this here? It doesn't need to be in the prelude. Just
> | leave it for the user to define (and then the user may pick
> | better names, like Ringad, zero, and <+>). -- P
>
> 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?
Simon
