haskell笔记(2)

–module Picture where

–或module Picture {

Picture,

above,

sideByside,

filpV,

filpH,

pic1,pic2,

printPic

} where

foo :: Int -> Int

foo x = x ^mod ^2

–[foo x | x <- [2,3,2,4,3,3,12]] <==> map foo

–[f x | x <- xs]

–高阶函数,highorder

my_map :: (a -> b) -> [a] -> [b]

–my_map f xs = [f x | x <- xs]

my_map f [] = []

my_map f (x : xs) = (f x) : map f xs

boo :: Float -> Bool

boo x = x^2 > 10

–map boo [1..10]

–map boo [True, False]

–p :: a -> Bool 类型的函数可以表达某种性质

–另一种计算模式：[x | x <- xs, p x]

isEven :: Int -> Bool

isEven x = x ^mod ^2 == 0

my_filter :: (n -> Bool) -> [a] -> [a]

–my_filter p xs = [x | x <- xs, p x]

–my_filter isEven [1..10]

my_filter p [] = []

my_filter p (x : xs)

| p x = x : my_filter p xs

| otherwise = my_filter p xs

–图形及图形上的函数

type Picture = [String]

picl = {

” # ”

” # # ”

” # # ”

” ####### ” }

–用”\n”换行

helpF :: Picture -> String

helpF [] = []

helpF (x : xs) = x ++ “\n” ++ heloF xs

printPic :: Picture -> IO ()

printPic pic = putStr (unlines pic)

sideByside :: Picture -> Picture -> Picture

sideByside pic1 pic2 = [x ++ y |(x,y) <- zip pic1 pic2]

above :: Picture -> Picture -> Picture

above pic1 pic2 = pic1 ++ pic2

flipV :: Picture -> Picture

filpV pic = [ reverse line | line <- pic]

filpV pic = map reverse pic

flipH :: Picture -> Picture

flipH :: pic = reverse pic

mys :: Picture -> Picture

mys pic = above pic1 pic1

where

pic1 = sideByside pic pic