Clojure - 副作用发生乱序 [英] Clojure - Side Effects Happening Out Of Order

问题描述

在Clojure中，我编写了一个非常基本的程序来回应用户键入的内容。然而，它不以我认为是自然的方式运行。这里是代码：

While dabbling in Clojure I've written a very basic program to echo whatever the user types into it. However, it doesn't run in a way that I'm perceiving to be natural. Here's the code:

(defn goo []
  (print "echo> ")
  (def resp (read-line))
  (print resp)
)

（对于我输入 foo 作为 read-line 的输入）：

user=> (goo)
echo> foo
foonil

但是，回显和读取线被切换：

But instead, the echo and read-line is switched:

user=> (goo)
foo
echo> foonil

为什么会发生这种情况？

Why does this happen? Is there a subtlety I'm missing?

编辑：从Joe的答案，更新的正确解决方案是：

From Joe's answer, the updated correct solution is:

(defn goo []
  (print "echo> ")
  (flush)
  (def resp (read-line))
  (print resp)
  (flush)
)

如果您使用 println 而不是打印，则必须这样。

Also, the flushes aren't necessary if you use println instead of print.

推荐答案

我什么也不知道clojure，但这听起来像一个缓冲区不能刷新的情况。找出如何刷完标准后打印。 println函数可能在每行结束时刷新。尝试：

I know nothing of clojure but this sounds like a case of buffers not getting flushed. Figure out how to flush standard out after the print. The println function probably flushes at the end of each line. Try:

(defn goo []
  (print "echo> ")
  (flush )
  (def resp (read-line))
  (print resp)
)

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