Documentation

Attempts to split the computation, giving access to the first result. Satisfies the following laws:

 msplit mzero                == return Nothing
 msplit (return a `mplus` m) == return (Just (a, m))

Fair disjunction. It is possible for a logical computation to have an infinite number of potential results, for instance:

 odds = return 1 `mplus` liftM (2+) odds

Such computations can cause problems in some circumstances. Consider:

 do x <- odds `mplus` return 2
    if even x then return x else mzero

Such a computation may never consider the 'return 2', and will therefore never terminate. By contrast, interleave ensures fair consideration of both branches of a disjunction

Fair conjunction. Similarly to the previous function, consider the distributivity law for MonadPlus:

 (mplus a b) >>= k = (a >>= k) `mplus` (b >>= k)

If 'a >>= k' can backtrack arbitrarily many tmes, (b >>= k) may never be considered. (>>-) takes similar care to consider both branches of a disjunctive computation.

Logical conditional. The equivalent of Prolog's soft-cut. If its first argument succeeds at all, then the results will be fed into the success branch. Otherwise, the failure branch is taken. satisfies the following laws:

 ifte (return a) th el           == th a
 ifte mzero th el                == el
 ifte (return a `mplus` m) th el == th a `mplus` (m >>= th)

Pruning. Selects one result out of many. Useful for when multiple results of a computation will be equivalent, or should be treated as such.