March 2021 1HaskellADay 1Liners

• 2021-03-23:

  You have [a] and (a -> IO b).

  You want IO [(a, b)]

  That is, you want to pair your inputs to their outputs for further processing in the IO-domain.

  • Chris Martin @chris__martin:

    \as f -> traverse @ [] @ IO (\a -> f a >>= \b ->

    return (a, b)) as

  • cλementd Children crossing @clementd:

    traverse (sequenceA . id &&& f)

    (actually, tranverse (sequence . (id &&& f)))

    Or p traverse (traverse f . dup)

• 2021-03-23: You have

  [([a], [b])]

  You want ([a], [b])

  so: [([1,2], ["hi"]), ([3,4], ["bye"])]

  becomes ([1,2,3,4],["hi","bye"])

  • karakfa @karakfa:

    conc xs = (concatMap fst xs, concatMap snd xs)