unsplit is an arrow that takes a pair of values and combines them to return a single value:
unsplit :: (Arrow a) => (b -> c -> d) -> a (b, c) d
unsplit = arr . uncurry
-- arr (\op (x,y) -> x `op` y) (***) combines two arrows into a new arrow by running the two arrows on a pair of values (one arrow on the first item of the pair and one arrow on the second item of the pair).
f *** g = first f >>> second g
Block quote:
foo bar