我可以避免“向右漂移”在Haskell？ [英] Can I avoid "rightward drift" in Haskell?

问题描述

当我使用命令式语言时，我经常写下像

When I use an imperative language I often write code like

foo (x) {
    if (x < 0) return True;
    y = getForX(x);
    if (y < 0) return True;

    return x < y;
}

也就是说，我逐条检查条件，尽可能快
。

That is, I check conditions off one by one, breaking out of the block as soon as possible.

我喜欢这个，因为它保持代码flat，并遵守end
weight的原则。我认为它更易读。

I like this because it keeps the code "flat" and obeys the principle of "end weight". I consider it to be more readable.

但是在Haskell我会写成

But in Haskell I would have written that as

foo x = do
    if x < 0
        then return x
        else do
            y <- getForX x

            if y < 0
                then return True
                else return $ x < y

我不喜欢那么多。我可以使用允许分解的monad，但
，因为我已经使用monad我必须提升一切，它添加词
我想避免，如果我可以。

Which I don't like as much. I could use a monad that allows breaking out, but since I'm already using a monad I'd have to lift everything, which adds words I'd like to avoid if I can.

我想没有真正完美的解决方案，但任何人都有
任何建议吗？

I suppose there's not really a perfect solution to this but does anyone have any advice?

推荐答案

对于你的具体问题：如何dangling do 符号和逻辑？

For your specific question: How about dangling do notation and the usage of logic?

foo x = do
  if x < 0 then return x else do
  y <- getForX x
  return $ y < 0 || x < y

编辑

说，你甚至可以得到更漂亮的代码：

Edit

Combined with what hammar said, you can even get more beautiful code:

foo x | x < 0     = return x
      | otherwise = do y <- getForX x
                       return $ y < 0 || x < y

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