在clojure中如何实现具有嵌套返回的循环？ [英] how would a loop with a nested return be implemented in clojure?

问题描述

我在这里玩一个狡猾的教程：

I'm playing around with a crafty tutorial here:

http://buildnewgames.com/introduction-to-crafty/

我想知道如何在Clojurescript / clojure

and am wondering how this particular function be implemented in clojurescript/clojure

 var max_villages = 5;
 for (var x = 0; x < Game.map_grid.width; x++) {
   for (var y = 0; y < Game.map_grid.height; y++) {
     if (Math.random() < 0.02) {
       Crafty.e('Village').at(x, y);

       if (Crafty('Village').length >= max_villages) {
        return;
       }
    }
  }
}

知道我们可以有（for []）构造，但是当max_villages命中5时如何让它停止？

I know that we can have the (for []) construct but how would you get it to stop when max_villages hits 5?

推荐答案

这里有一种方法：

(def max-villages 5)

(->> (for [x (range map-width)
           y (range map-height)]
       [x y])
     (filter (fn [_] (< (rand) 0.02)))
     (take max-villages))

然后可能添加（map make-village-at）或类似的下一阶段的管道;如果它的意图是执行副作用，添加 dorun 或 doall 作为最后阶段，迫使他们立即发生（根据返回值是否有趣，选择一个）。

Then perhaps add (map make-village-at) or something similar as the next stage of the pipeline; if it's meant to perform side effects, add a dorun or doall as the final stage to force them to happen at once (choosing one or the other depending on whether the return values are interesting).

注意。

使用计数器进行比较的更强制的方法：

A more imperative approach with a counter for comparison:

(let [counter (atom 0)]
  (doseq [x (range map-width)
          :while (< @counter max-villages)
          y (range map-height)
          :while (< @counter max-villages)
          :when (< (rand) 0.02)]
    (swap! counter inc)
    (prn [x y]))) ; call make-village-at here

：while 当其测试表达式失败时，在当前嵌套级别终止循环; ：当立即移动到下一个迭代。 doseq 也支持分块，但：while 将阻止它执行不必要的工作。

:while terminates the loop at the current nesting level when its test expression fails; :when moves on to the next iteration immediately. doseq supports chunking too, but :while will prevent it from performing unnecessary work.

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