B.3 Combinators, plumbing

>==< :: F a b -> F c a -> F c b,
serial composition.
>+< :: F a b -> F c d -> F (Either a c) (Either b d),
parallel composition of two fudgets, which can be of different type.
listF :: (Eq a) => [(a, F b c)] -> F (a, b) (a, c),
parallel composition of a list of fudgets. All parts must have the same type.
loopThroughRightF :: F (Either a b) (Either c d) -> F c a -> F b d,
a loop combinator for encapsulation.
More combinators for plumbing are presented in Chapter 17 and 18.