Re: laws for MonadPlus?

[Ralf Hinze]

> what laws should hold for the (++) operation?

Associativity and leftward distributivity are missing in the Report:

        (m ++ n) ++ o   =  m ++ (n ++ o)

        (m ++ n) >>= k  =  (m >>= k) | (n >>= k)

On the other hand right distributivity does not hold in general.
Conversely, the report also requires zero to be a right zero of >>
which I do not support (if you combine backtracking and exception
handling you probably expect raise e >> zero = raise e ).

HTH, Ralf