haskell learning1(2)

最新推荐文章于 2024-04-26 09:56:29 发布

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本文介绍了函数式编程的基本概念，包括列表推导、类型定义、函数定义等核心内容，并通过具体示例展示了如何使用这些概念来解决实际问题。

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[x^2| x<- [1..10],odd x]==[1,9,25,49,81]

[z| x <- [1..10],let z = x^2,z>50] # kann Abkürzung für oben

2.[(wert,name)| wert <- [1..3],name <- ['a'..'b']]

result:

[(1,'a'),(1,'b'),(2,'a'),(2,'b'),(3,'a'),(3,'b')]
it :: (Enum t, Num t) => [(t, Char)]

3. type MyWeirdType = (Double,[(Bool,Integer)])

4.data MyTuple = MyTupelConstructor Int Int

##wie Tupel ohne Klammern und kommas;stattdessen mit vorangestellem Konstruktor

5.    data Frucht = Apfel (Int,Double)
                             | Birne Int Double
                             | Banane Int Int Double

data Maybe a = Noting | Just a

data Frucht = Apfel {preis::Int,anzahl::Int}
   | Birne {preis::Int,anzahl::Int}
   |Banane {preis::Int,anzhal::Int
     ,krümmung:Double}

getKrümmung :: Frucht -> Maybe Double
getKrümmung Banane {krümmung=k} = Just k
getKrümmung _ = Nothing

1. Maybe

example :

data Maybe a = Nothing | Just a

isJust      :: Maybe a -> Bool
isJust   Nothing = False
isJust   _        = True

2.Either

example:

Module Data.Either where
data Either a b = Left a | Right b

isRight :: Either a b -> Bool
isRight (Left _) = False
isRight (Right _) = True

lefts :: [Either a b]-> [a]
lefts x = [a | Left a <- x]

partitionEithers :: [Either a b]-> ([a],[b])
partitionEithers [] = ([],[])
partitionEithers (h:t)
  | Left l <- h = (l:ls,rs)
  | Right r <- h = (ls,r:rs)
  where (ls,rs) = partitionEithers t

#just example

Funktionsdefinition

double1 x = x+x
foo x y z = x +y *double z
add = \x y -> x +y

twice f x = f x x
double2 y = twice (+) y
double3 = twice (+)

2.Höhepunkt

Int -> Int -> Int gleich as Int->(Int -> Int)

drop :: Int -> [a]->[a]
drop n xs | n <= 0 = xs
drop _ [] = []
drop n (_:xs) = drop (n-1) xs

drop 3 [1,2,3,4,5]

Einrückung ersetzt Klammerung

betragSumme :: Int -> Int -> Int
betragSumme x y =
let x' = abs x
  y' = case y of 0 -> 0
      x| x>0 ->x
       | otherwise -> -x
  in x' + y'

map :: (a->b)->[a]->[b] # (a->b) funktion
map f [] = []
map f (x:xs) =
f x : map f xs