Tuesday, April 11, 2017

March 2017 1HaskellADay 1Liners

  • March 30th, 2017:
    divide :: (a -> Either b c) -> [a] -> ([b], [c])  This function is somewhere easy to get to, right?
    via @fmapE 
    • @fmapE: divide f = foldr (either (first . (:)) (second . (:)) . f) ([], []) 
    • SocialJusticeCleric @walkstherain divide f = Data.Either.partitionEithers . fmap f
    • andrus @andrus divide f = foldMap $ (swap . pure . pure ||| pure . pure) . f
    • matt @themattchan divide = partitionEithers ... map where ... = (.).(.)
  • March 13th, 2017:
    Palindromes have nothing to do with today's #haskell problem of anagrams. So what.

    Define
    palindrome :: String -> Bool
    elegantly
    • SocialJusticeCleric @walkstherain all id . (zipWith (==) =<< reverse)
      • SocialJusticeCleric added: TIL Data.Foldable.and
    • bazzargh @bazzargh ap (==) reverse?
  • March 13th, 2017:
    type Bag a = Map a Int

    anagram :: Ord a => [a] -> [a] -> Bool
    anagram src = (== Bag.fromList src) . Bag.fromList

    Redefine with <*>
    • Denis Stoyanov @xgrommx why not?
      anagram = (==) `on` Bag.fromList

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