Thursday, July 14, 2016

1HaskellADay 1Liners June 2016

  • June 13th, 2016:
    You want this list: [1, -1, 1, -1, ...]
    How would you produce this value in #Haskell ?
    • Wai Lee Chin Feman @wchinfeman
      https://gist.github.com/skatenerd/08d70c45499e1610206a
      (set plop to be identity, and set transformstate to be (*) -1)
    • Philipp Maier @AkiiZedd `iterate negate 1
    • Patrick Mylund @pmylund concat $ repeat [1, (-1)]
      • Gary Fixler @gfixler No need for the parens in a list.
    • Jeff Foster @fffej and Kevin Meredith @Gentmen
      iterate (* (- 1)) 1
    • Spencer Janssen @spencerjanssen and Андреев Кирилл @nonaem00
      cycle [1, -1]
      • Philipp Maier @AkiiZedd:
        I’m curious: Since concat is O(n) wouldn’t it take more and more time depending on how many items you take?
      • Patrick Mylund @pmylund Looks like they compile to the same thing https://gist.github.com/patrickmn/9a92ab2a088018b2c0631f3bcfd60ebe
      • Philipp Maier @AkiiZedd I’m actually surprised the compiler can optimise this away :o Thanks for showing me ddump-simpl!
      • Eyal Lotem @EyalL concat is foldr (++), not foldl. O(1) work is done to produce the next item. [1,-1]++([1,-1]++(...
    • David Turner @DaveCTurner I'd actually write 'cycle [1,-1]' but I like the elegant, alliterative obscurity of   'iterate negate 1'
    • Fatih Karakurt @karakfa alt=1:[-x|x<-alt]

1 comment:

Unknown said...

x = 1 : -1 : x

or

(let x = 1 : -1 : x in x)