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Haskell

Haskell. Lite mera om listor . Skapa en lista mha ett delintervall. Prelude> [1 ..8 ] [1,2,3,4,5,6,7,8 ] Prelude> [1.1 .. 2.2] [1.1,2.1 ] Prelude> [1.1 .. 4.2] [1.1,2.1,3.1,4.1 ] Prelude> [1,3 ..10] [1,3,5,7,9]. Steglängd : default 1 Sista elementet närmast slutgränsen.

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Haskell

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  1. Haskell Lite mera om listor

  2. Skapa en lista mha ett delintervall Prelude> [1 ..8] [1,2,3,4,5,6,7,8] Prelude> [1.1 .. 2.2] [1.1,2.1] Prelude> [1.1 .. 4.2] [1.1,2.1,3.1,4.1] Prelude> [1,3 ..10] [1,3,5,7,9] Steglängd: default 1 Sistaelementetnärmastslutgränsen Du kandefinierasteglängdensjälv implicit

  3. Skapa en lista mha ett delintervall Prelude> [1.1, 1.2 .. 2.4] [1.1,1.2,1.2999999999999998,1.3999999999999997,1.4999999999999996,1.5999999999999994,1.6999999999999993,1.7999999999999992,1.899999999999999,1.999999999999999,2.0999999999999988,2.1999999999999984,2.299999999999998,2.3999999999999977] Intesåexaktnärdetgällerflyttal ...

  4. List comprehension • En kraftfullmekaniskförattskapalistor • Syntax (jfrmatematiskstandardnotation; <- skatolkassom∈ Prelude> let ex = [1..10] Prelude> ex [1,2,3,4,5,6,7,8,9,10] Prelude> let x2 = [2*x| x <- ex] Prelude> x2 [2,4,6,8,10,12,14,16,18,20]

  5. List comprehension • Du kanocksåanvändafunktioneri list comprehensions: Prelude> let isEvenn = (n `mod` 2 == 0) Prelude> :info isEven isEven :: Integral a => a -> Bool -- Defined at <interactive>:22:5 Prelude> let evenEx = [isEvenx| x <- ex] ex = [1..10] Prelude> evenEx [False,True,False,True,False,True,False,True,False,True] Prelude> let evenEx = [isEvenx| x <- x2] ex2 = [2,4..20] Prelude> evenEx [True,True,True,True,True,True,True,True,True,True]

  6. List comprehension • Du kansättavillkor till generatorn: Prelude> let exBig = [x | x <- x2, x >= 10] Prelude> exBig [10,12,14,16,18,20] Prelude> let ex = [1..100] Prelude> let testL = [x | x <- ex, isEvenx, x > 60] Prelude> testL [62,64,66,68,70,72,74,76,78,80,82,84,86,88,90,92,94,96,98,100]

  7. List comprehension • Du kananvändaettmönsteriställetför en variabelpå den vänstrasidanavpilen: Prelude> let parPlus = [x+y | (x,y) <- [(1,1),(2,2),(4,4)]] Prelude> parPlus [2,4,8]

  8. List comprehension • Du kan ha tvågeneratorerochkombineraderasresultat, här till en kartesiskprodukt: Prelude> let paraxy = [(x,y) | x <- [1..5], y <- [1..5]] Prelude> paraxy [(1,1),(1,2),(1,3),(1,4),(1,5),(2,1),(2,2),(2,3),(2,4),(2,5),(3,1),(3,2),(3,3),(3,4),(3,5),(4,1),(4,2),(4,3),(4,4),(4,5),(5,1),(5,2),(5,3),(5,4),(5,5)] Prelude> let testL = [x - y | x <- [1..5], y <- [2,4..10]] Prelude> testL [-1,-3,-5,-7,-9,0,-2,-4,-6,-8,1,-1,-3,-5,-7,2,0,-2,-4,-6,3,1,-1,-3,-5]

  9. List comprehension • Obs! Om du villsubtraheraelementenparvis, dvsförsta element – första element, andra element – andra element etc. finnsdetandraoperationerfördetta! (Se zip ochzipWith) Prelude> let l1 = [1..5] Prelude> let l2 = [2,4..10] Prelude> :info zip zip :: [a] -> [b] -> [(a, b)] -- Defined in `GHC.List' Prelude> let l3 = zip l1 l2 Prelude> l3 [(1,2),(2,4),(3,6),(4,8),(5,10)] Prelude> let l4 = [a-b | (a,b) <- l3] Prelude> l4 [-1,-2,-3,-4,-5]

  10. List comprehension • Vi kanocksågöradettaännusnyggareutan list comprehension när vi tittarmerapåhögreordningensfunktioner: Prelude> l1 [1,2,3,4,5] Prelude> l2 [2,4,6,8,10] Prelude> let l5 = zipWith (-) l1 l2 Prelude> l5 [-1,-2,-3,-4,-5]

  11. List comprehension • Vi kananvändalist comprehension ifunktionsdefinitioner: Prelude> let addOrdPairspairList = [m+n | (m,n) <- pairList, m < n] Prelude> :info addOrdPairs addOrdPairs :: (Num t, Ordt) => [(t, t)] -> [t] -- Defined at <interactive>:55:5 Prelude> addOrdPairs [(1,1), (1,2), (2,3), (4,2)] [3,5]

  12. List comprehension • Vi kananvändalist comprehension ifunktionsdefinitioner: Prelude> let allEvenxs = (xs == [x | x <- xs, isEvenx]) Prelude> :info allEven allEven :: Integral a => [a] -> Bool -- Defined at <interactive>:58:5 Prelude> allEven [1..10] False Prelude> allEven [2,4..20] True Prelude> allEven [2,4..19] True 19 ärej med ilistan!

  13. List comprehension • Vi kananvändalist comprehension ifunktionsdefinitioner: Prelude> let singletons xss = [x | [x] <- xss] Prelude> :info singletons singletons :: [[t]] -> [t] -- Defined at <interactive>:63:5 Prelude> singletons [[], [1], [2], [3,4,5], [2,4], [6,7,8], [9]] [1,2,9] Observerahurmönsteranpassninganvändshär!

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