如何实现无点交互？

发布于 2024-12-04 01:18:29 字数 386 浏览 1 评论 0原文

shortLinesOnly :: IO ()
shortLinesOnly = interact result
    where
        shortLength     = 11
        onlyShorts      = (<= shortLength) . length
        shortLines      = filter onlyShorts . lines
        result          = unlines . shortLines
        interact result = getContents >>= putStr . result

在上面的代码中，我如何以点自由风格编写interact函数。

原文

shortLinesOnly :: IO ()
shortLinesOnly = interact result
    where
        shortLength     = 11
        onlyShorts      = (<= shortLength) . length
        shortLines      = filter onlyShorts . lines
        result          = unlines . shortLines
        interact result = getContents >>= putStr . result

In the above code how can I write the interact function in point free style.

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ぽ尐不点ル 2024-12-11 01:18:29

步步：

interact r = getContents >>= putStr . r
interact r = (getContents >>=) (putStr . r)
interact r = (getContents >>=) $ (putStr .) $ r
interact = (getContents >>=) . (putStr .)

Step by step:

interact r = getContents >>= putStr . r
interact r = (getContents >>=) (putStr . r)
interact r = (getContents >>=) $ (putStr .) $ r
interact = (getContents >>=) . (putStr .)

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与往事干杯 2024-12-11 01:18:29

最好的答案是：不要。对于这个特定的示例，唯一会发生的变化是您的代码的可读性会降低。你原来的尖头变体非常好。

在某些情况下，最好避免 pointfree 风格。这是其中之一，因为你的论点不经历线性数据流。它更适合用来为其他东西构建数据流。例子：

-- Bad: Pointy linear data flow description.
chunksOf :: Int -> [a] -> [[a]]
chunksOf n xs =
    takeWhile (not . null) (map (take n) (iterate (drop n) xs))

-- Good: Pointfree linear data flow description.
chunksOf :: Int -> [a] -> [[a]]
chunksOf n =
    takeWhile (not . null) . map (take n) . iterate (drop n)

-- Bad: Now exaggerating with pointfree style.
chunksOf :: Int -> [a] -> [[a]]
chunksOf =
    liftA2 ((.) (.) . (.) $ takeWhile (not . null))
           (map . take)
           (iterate . drop)

The best answer is: Don't. For this particular example the only change that would make is that your code would be less readable. Your original pointy variant is perfectly fine.

In certain cases it is better to avoid pointfree style. This is one of them, because your argument does not undergo linear data flow. It is rather used to build the data flow for something else. Example:

-- Bad: Pointy linear data flow description.
chunksOf :: Int -> [a] -> [[a]]
chunksOf n xs =
    takeWhile (not . null) (map (take n) (iterate (drop n) xs))

-- Good: Pointfree linear data flow description.
chunksOf :: Int -> [a] -> [[a]]
chunksOf n =
    takeWhile (not . null) . map (take n) . iterate (drop n)

-- Bad: Now exaggerating with pointfree style.
chunksOf :: Int -> [a] -> [[a]]
chunksOf =
    liftA2 ((.) (.) . (.) $ takeWhile (not . null))
           (map . take)
           (iterate . drop)

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