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如何使用fold在Haskell中實現takeWhile函數?實施takeWhile摺疊
takeWhile :: (a -> Bool) -> [a] -> [a]
我嘗試了戰略類同實施過濾器這樣
filter :: (a -> Bool) -> [a] -> [a]
filter f = foldr (\x acc -> if f x then x : acc else acc) []
但我怎麼能停在f x是假的?