The `>.<` combinator

The combinator

   (>.<) :: F a b -> F c d -> F (a, c) (b, d)

sends components to the corresponding subfudgets, and output a pair whenever one subfudget outputs a message, if the other subfudget has output a message at all. Its definition is

infixl 5 >.<
a >.< b = combine2SP >^^=< (a >+< b) >=^^< splitSP

combine2SP :: SP (Either a b) (a,b)
combine2SP = comb Nothing Nothing where 
   comb ma mb = 
     (case (ma,mb) of
	(Just a,Just b) -> putSP (a,b)
	_ -> id) $ 
     getSP $ \y -> case y of
	  Left a -> comb (Just a) mb
	  Right b -> comb ma (Just b)

The >.< combinator

The `>.<` combinator