haskell-kadai-5.md

5 高階関数　課題

下記length', all'をfoldl, foldr, foldl1, foldr1のいずれかを用いて実装せよ。 length', all'の挙動はlength, allを参照すること。

length' :: [a] -> Int

all' :: (a -> Bool) -> [a] -> Bool 

main = do
    print $ length' [1,2,3,4] 
    print $ length' $ replicate 100 1
    print $ all' even [2,4,6]
    print $ all' even [2,4,7]
    print $ all' even [1,3..]

Output:

4
100
True
False
False