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haskellfunctorapplicative

How can I use functors or applicatives to rewrite this Haskell function over lists of tuples

Is there a nicer way to write the following function fs' with functors or applicatives?

fncnB = (* 2)
fncnA = (* 3)
fs' fs = zip (map (fncnA . fst) fs) $ map (fncnB . snd) fs

I see from this question that I could rely on the functor instance of lists to map a single function acting over both elements of each tuple, or e.g. on the applicative instance of tuples to apply functions to just the second-half of a two-tuple, but I'm curious how functors and applicatives fit into the picture of operating over lists of multi-component data types.

Solution

  • A tuple is a bifunctor, so bimap is available.

    import Data.Bifunctor

fncnB = (* 2)
fncnA = (* 3)
fs' = map (bimap fncnA fncnB)

    No third-party libraries required.