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]

Friday, July 1, 2016

June 2016 1HaskellADay Problems and Solutions

  • June 29th, 2016: Today's #Haskell exercise is REALLY HARD! ... for Big Gov't. Can you solve it? A little bit of (well-typed) Prolog-like code gets us our #haskell solution for today 
  • June 28th, 2016: For today's #haskell problem we do ... NOTHING! But we are introduced to coding software for a huge bureaucracy  ... AAAAANNNDDD three System imports and we've got today's #haskell solution. Groovy! 
  • June 24th, 2016: #haskell problem today charts Stochastic Oscillators of a security  and includes a 'malus' problem: report generation 
  • June 23rd, 2016: Today we look at using #haskell to chart moving averages of a stock's prices https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D23/Exercise.hs https://twitter.com/logicalgraphs/status/743409829843243008 
  • June 21th, 2016: I pushed today's #haskell problem last night on git but did I announce it? sigh Complex roots of quadratic equations https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D21/Exercise.hs The #haskell solution gives us the Complex roots to any (Real) quadratic equation https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D21/Solution.hs
  • June 20th, 2016: Solving quadratic equations is on the plate for today's #haskell exercise https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D20/Exercise.hs 
    It's not every day I code
    Thank you, #haskell, for today's solution to do so
    https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D20/Solution.hs
  • June 17th, 2016: My, my! Where has the day flown? Today's #haskell problem is to reinvent charting API! ... or not. https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D17/Exercise.hs
  • June 16th, 2016: Today's #haskell exercise looks at representing $TWTR data as candlesticks https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D16/Exercise.hs 
  • June 15th, 2016: For today's #haskell problem, we round out the Data.Matrix module with the definition of the identity matrix https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D15/Exercise.hs There are many ways to define the identity matrix. Today's #haskell solution does so with Cellular Automata Rule 16 https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D15/Solution.hs
  • June 14th, 2016: Yesterday we computed the matrix determinant, today we'll invert a matrix and use it to solve systems of equations https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D14/Exercise.hs Today's #haskell solution inverts a matrix BECAUSE WE FEEL LIKE IT! Yeah https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D14/Solution.hs
  • June 13th, 2016: For today's #haskell problem we *ahem* DETERMINE (eventually) to solve systems of equations https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D13/Exercise.hs The determinant is the sum of the products of the first row with the sub-matrix determinants, right? RIGHT! https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D13/Solution.hs
  • June 10th, 2016: Today's #haskell problem looks at box-and-whiskers charting of data https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D10/Exercise.hs Boxes for realz, yo: https://en.wikipedia.org/wiki/Box_plot The #haskell solution has @geophf writing 'uncurry uncurry' and sincerely meaning it! 😱 https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D10/Solution.hs and box: 
  • June 9th, 2016: Triangles are on my mind for today's #haskell problem: https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D09/Exercise.hs … bisecting them, then trisecting them.
  • June 8th, 2016: For today's #haskell problem, just what you've always wanted: MATH HOMEWORK! We find the intersection of two lines https://github.com/geophf/1HaskellADay/blob/master/exercises/HAD/Y2016/M06/D08/Exercise.hs
  • ANNOUNCEMENT: lpaste.net is acting up; cloning original @1HaskellADay github repository and putting the exercise there. FYI
  • June 6th, 2016: Today's #haskell problem explores superstring theory http://lpaste.net/6891096377267322880 No, it doesn't, but saying that has a certain ring to it!
  • June 3rd, 2016: We saw a solution to perfect matching yesterday. For today's #haskell problem, let's efficient-ize it! http://lpaste.net/1128504074363207680
  • June 1st, 2016: Today's #haskell problem is pretty much counting complements ... pretty much. http://lpaste.net/9130195410017583104 These apparently simple problems are actually rather hard. Today we have a #P-complete #haskell solution http://lpaste.net/670419007353913344

Tuesday, June 14, 2016

May 2016 1Liners

One-liners
  • May 24th, 2016:
    Given f :: a -> [a] -> b, g :: a -> c
    Write h :: c -> [c] -> b, point-free, in terms of f and g
    where h x y = f (g x) (map g y)
  • May 16th, 2016: The next 3 #1Liner are of a piece, using
    data CmpV a =
       Vec { len :: Int, top :: a,  elts :: [a],
             cmp :: CmpV a -> CmpV a -> Ordering }
    • Give the point-free definition of:
      twoVs :: CmpV a -> CmpV b -> ([a], [b])
    • instance Ord (CmpV a) where
         compare v1 = uncurry (cmp v1) .  (v1,)

      Make compare point-free by removing v1 from above definition
    • An Ord-instance needs an Eq-instance:
      instance Eq a => Eq (CmpV a) where
         v1 == v2 = elts v1 == elts v2

      point-free-itize (==)
  • May 16th, 2016: You have the following lambda:
    \x y -> x == y || fn x y
    where fn :: a -> a -> Bool
    Point-free-itize
    • obadz @obadzz without any fancy uses of the (a ->) Applicative :)
      curry $ foldr (||) False . flip map [(==), fn] . flip uncurry
    • obadz @obadzz with fancy use of (a ->) Applicative :)
      curry $ liftA2 (||) (uncurry (==)) (uncurry fn)
    • Noah Luck Easterly @walkstherain
      curry $ uncurry (||) . (uncurry (==) &&& uncurry fn)
  • May 5th, 2016:
    sames :: Eq a => [a] -> [a] -> Int
    Counts equal values at the same indices in two lists.
    What is the point-free definition?
    • joomy @cattheory
      sames = curry (length . filter (uncurry (==)) . uncurry zip)
    • bazzargh @bazzargh and then Fatih Karakurt @karakfa
      ((length . filter id) .) . zipWith (==)
    • me: sum <<- fromenum="" li="" nbsp="" zipwith="">
    • Noah Luck Easterly @walkstherain
      sames = ((sum . map fromEnum) .) . zipWith (==)
      • `getSum . foldMap (Sum . fromEnum)` seems better than `foldr (bool id succ) 0` but both satisfy `[Bool] -> Int`
    • Андреев Кирилл @nonaem00
      let it = (length .) . (filter id .)  . zipWith (==)

Wednesday, June 1, 2016

May 2016 1HaskellADay Problems and Solutions

May 2016

  • May 31st, 2016: Today's #haskell problem gets a subsequence of DNA from ... DNA! http://lpaste.net/1527607897389793280 Today's #haskell solution: DNA subsequence GOT http://lpaste.net/5828328688629841920
  • May 30th, 2016: We find the number of RNA strands that can generate a protein ... modulo reasonableness for today's #haskell problem http://lpaste.net/7114368903530151936 Today's #haskell solution shows us there are 'more than a few' RNA strands to compose some proteins http://lpaste.net/3827843057999413248
  • May 27th, 2016: For today's #haskell problem we sing: No woman, Nah Trie! http://lpaste.net/8137189406290214912 Or: Breath-first Trie Traversal via the branches. We take breathing-lessons for today's #haskell solution http://lpaste.net/2088953736360624128
  • May 26th, 2016: For today's #haskell problem we label the nodes of a Trie ... http://lpaste.net/658981668358455296 or at least we ... TRIE to! *groan Today's #haskell solution is a depth-first traversal of a Triehttp://lpaste.net/7964088321452277760
  • May 25th, 2016: Today's #haskell problem ask you to exercise your probability muscles and look at some allele-pairingshttp://lpaste.net/7098281613896712192 That's all.
  • May 24th, 2016: Reverse Palindromes in DNA strands?Yes. http://lpaste.net/4547532761941934080 Today's #haskell problem. Turns out there are lots of palindromes in DNA strands as today's #haskell solution shows. http://lpaste.net/8959978868165312512 Go figure.
  • May 23rd, 2016: Splice, splice, baby! We get all Vanilla Ice with RNA with today's #haskell problem http://lpaste.net/2811938573572374528 We get our protein when with today's hand-rolled List-y-(\\) #haskell solution http://lpaste.net/5823105188059152384
  • May 20th, 2016: For today's #haskell problem we consider the weighty matter of ... weighing matter http://lpaste.net/7500383126527410176 The weight's the thing Wherein I'll catch the conscience of the King ... no ... weight ...Today's #haskell solution http://lpaste.net/7743348996965400576
  • May 19th, 2016: Today's #haskell problem looks at the Carmina Buranahttp://lpaste.net/684224423812661248 ... uh, no, it doesn't: Open Reading Frames.  Today's #haskell solution sequences DNA strands to proteins http://lpaste.net/792645775074000896
  • May 18th, 2016: If at first you do not succeed, trie and trie again today's #haskell problem http://lpaste.net/8558987235213443072 #trie #datatype 
  • May 17th, 2016: "Houston. We have a problem." #bigdata factors into today's #haskell problem of longest monotonic sequenceshttp://lpaste.net/6778179741435297792
  • May 16th, 2016: Today's #Haskell problem asks for longest monotonic increasing/decreasing sequences ... in the small ... http://lpaste.net/7252474989977272320 So, the #haskell solution works against small data set, but since it's bifurcating, against large data sets? ... http://lpaste.net/7003206401061289984
  • May 13th, 2016: #Rosalind is impatient. She doesn't have all day! Let's find a real-world solution to today's #haskell problem http://lpaste.net/8254705170412208128 Finding the longest common gene subsequence of 100 strands each 1000 nucleotides long in #haskell http://lpaste.net/2468395370904813568 Can you find faster?
  • May 12th, 2016: We propose a little problem from Set Theory for today's #haskell problem http://lpaste.net/4050317579338645504 And we have today's #haskell in-a-perfect-world solution of the set-intersection of all subsequenceshttp://lpaste.net/1682855623517011968
  • May 11th, 2016: Today's #haskell problem is all about the inods ... not 'inodes,' but 'internal nodes of an unrooted binary tree.' http://lpaste.net/7455193258755358720 "inods?" you say? "Of an unrooted binary tree?" you say? That would be pred . pred for today's #haskell solution http://lpaste.net/4766815087493120000
  • May 10th, 2016: For today's #haskell problem we take it to the next level, see? and get variable-length strings as enumerated tokens http://lpaste.net/3180555571975684096 We pulled the powerSet Set.fromList Set.toList switcheroo for today's #haskell solution. http://lpaste.net/7501776843414962176
  • May 9th, 2016: For today's #haskell problem we sing our A, B, Cs ... #Rosalind-style! http://lpaste.net/1445499963915108352 Today's #Haskell solution enumerates lexed tokens http://lpaste.net/503582828101894144
  • May 6th, 2016: For today's #haskell problem we ask #Rosalind and she says 'Permutations.' So that's what we do! http://lpaste.net/6558920694606856192 This is the dawning of the age of Aquarius! "Hair" a movie about perms for today's #haskell solution http://lpaste.net/934285743432400896 @NickiElson3D 
  • May 5th, 2016: Today's #haskell problem: p-distance Matriceshttp://lpaste.net/818771459840147456 Believe you me: you will get a LOT of continued employment with these Today's #haskell solution is filed under #jobsecurity http://lpaste.net/5076187573303377920 #distanceMatrix
  • May 4th, 2016: Today's #haskell problem we look at completing a graph into the Tree of Life http://lpaste.net/1315899789614776320 #Rosalind Today's #haskell solution is graph-y, or also take the approach of @bazzargh http://lpaste.net/1052721051462533120
  • May 3rd, 2016: Today's #haskell problem looks at overlapping graphs, specifically for DNA strands from rosalind.info http://lpaste.net/8920617631791185920 Did you know a list is a graph? Today's #haskell solution was an elaboration of `isSuffixOf` http://lpaste.net/5785600391169179648 #Rosalind 
  • May 2nd, 2016: For today's #haskell problem we look at transforming our data into d3: "Data-driven document"-JSONhttp://lpaste.net/224067301371019264 For the #haskell solution we get a bird's-eye view of the Top5s stocks http://lpaste.net/7060337987313205248 

Thursday, May 5, 2016

April 2016 1HaskellADay 1Liners

  • April 15th, 2016:
    (\(intensf, list) -> map (second intensf) list) (insensifierFn, assocList)
    Point-free-itize this lambda
    • obadz @obadzz uncurry $ map . second
  • April 15th, 2016:
    foldr (\card -> let c = color card in mappend c *** ((idx card, c):))
           (mempty, []) cards
    Point-free-itize and de-let lambda
    • Gautier DI FOLCO @gautier_difolco foldr (uncurry (***) . (uncurry fmap . fmap (((,) =<< mappend) . color) . ((,) =<< ((:) .) . (,) . idx))) (mempty, []) cards
    • me: foldr (uncurry (***) . (mappend . snd &&& (:)) . (idx &&& color)) (mempty, [])
  • April 15th, 2016: map (\(idx, color) -> C idx (cell bb idx) color) assoclist
    point-free-itize the lambda in the map function.
    • Eyal Lotem @EyalL uncurry (C <*> cell bb) ?
      Not in front of a type checker, can't check myself :)
  • April 13th, 2016:
    point-free-itize lambda term in:
    uncurry (foldr (\a -> min a *** max a)) . ((head &&& head) &&& id)
    • obadz @obadzz liftA2 (***) min max
  • April 12th, 2016:
    minmax :: Ord a => [a] -> (a, a)
    minmax [1..9] = (1,9)
    in linear time.
    minmax = minimum &&& maximum
    fails as it's 2x too slow.
  • April 12th, 2016:
    You have (a,b) (c,d)
    You need (a*c, b*d)

    Well, we don't have all day! (Actually, we do) Get to it!
    Pointless; I MEAN POINT-FREE pls
    • lotz@Haskell㌠ @lotz84_ ((uncurry . flip . curry $ id).) . ((uncurry.) . uncurry . (flip.) . flip . flip) ((((flip . (flip.)) $ ((,).) . (*)).) . (*))
    • Olivier Iffrig @oiffrig Point-free but star-full: uncurry (***) . ((*) *** (*))
    • bazzargh @bazzargh curry((uncurry (*)) *** (uncurry (*)))
    • bazzargh @bazzargh knew there had to be a bimap answer, eventually got: curry ((bimap <$> id <*> id) (uncurry (*)))
    • obadz @obadzz join biliftA2 (*)
    • Андреев Кирилл @nonaem00 (((product *** product) . unzip) .) . (flip (:)) . (:[]) ... I clearly need more coffee this morning.
  • April 10th, 2016:

    data BBx = Bx (Int, Int) Pt2D Pt2D

    define:
    mkBB :: [a] -> Pt2D -> BBx
    mkBB xs extents = Bx (0, length xs) (0,0) extents
    points-free
    • Gautier DI FOLCO @gautier_difolco
      -- LANGUAGE TupleSections
      data BBx = Bx (Int, Int) Pt2D Pt2D
      mkBB :: [a] -> Pt2D -> BBx
      mkBB = flip Bx (0,0) . (0, ) . length
    • Thomas D @tthomasdd mkBB = flip Bx (0,0) . (,) 0 . length
  • April 7th, 2016:
    type MList a n = [(a, n)]
    partSz :: Ord n => n -> MList a n -> (MList a n, MList a n)
    partSz µ = partition ((µ >) . snd)
    Define points-free
    • partSz = partition . (. snd) . (>)  -- via @gautier_difolco

Monday, May 2, 2016

April 2016 1HaskellADay Problem and Solutions

April 2016

Thursday, April 7, 2016

March 2016 1HaskellADay 1Liners

One-liners
  • March 29th, 2016: You have a list, Show a => [a], of known-length n, n > 100 Show the first three and the last three elements of that list
  • March 28th, 2016: You have f :: c -> d and g :: a -> b -> c
    define (<<-) such that f <<- g is f (g a b)
    Does it exist already (in the Prelude, maybe)?
  • March 26th, 2016: insert1 :: Ord k => k -> a -> Map k [a] -> Map k [a] define, points-free, efficiently. (hint: it's not insertWith)
  • March 26th, 2016: sqDist :: Fractional ä => [ä] -> [ä] -> ä sqDist v1 v2 = sum (zipWith (\a b -> (a - b) ^2) v1 v2) Point-free-itize sqDist (and λ)
  • March 17th, 2016: for f :: (a -> b) -> (a, a) -> (b, b) define f
    • obadz @obadzz f = join bimap
  • March 17th, 2016: removeAll :: Eq a => a -> [a] -> [a]; define
    e.g.: removeAll '"' "(\"S312\", \"S204\")" ~> "(S312, S204)"
    • obadz @obadzz removeAll = filter . (/=)
    • Gautier DI FOLCO @gautier_difolco ... same
  • March 17th, 2016:
    f, g :: (String, String) -> String
    let ab = ("a", "b")
    f ab ~> "(\"a\", b)"
    g ab ~> "(a, \"b\")"
    define h that generalizes f and g
    • Gautier DI FOLCO @gautier_difolco
      cp x y (a,b) = concat ["(", x a, ",", y b, ")"]
      f,g :: (String, String) -> String
      g = cp id show
      f = cp show id