Aaron Denney wrote:
You can, but the "other one" turns it into a copy of the Maybe Monad, so the current one is more useful.
So what does this mean in terms of Ashley's question: But only some instances (such as []) satisfy this: (mplus a b) >>= c = mplus (a >>= c) (b >>= c) Other instances (IO, Maybe) satisfy this: mplus (return a) b = return a Does it mean that both fall within the acceptable definition of the monad laws for MonadPlus? 1. |mzero >>= f == mzero| 2. |m >>= (\x -> mzero) == mzero| 3. |mzero `mplus` m == m| 4. |m `mplus` mzero == m| So I guess I must have missed the point because the distinction between say a monad on [] and Maybe for example seems to me to be irrelevant to MonadPlus. The distinction comes down to mplus being the same as skipError for Maybe and different for []. Keean.