条件照应收集最佳实践？
我尝试迭代一个序列，有条件地对每个元素执行操作，然后收集它（但前提是它符合条件）。这是一个有效的简化示例，我只是想知道这在 lisp 中是否正确或最佳实践：
(loop for n in '(1 2 3 4 5)
when (when (equal (mod n 2) 0) n )
collect it)
yields
(2 4)
这有效，它对我来说看起来很有趣，而不是何时-何时，而是因为我觉得我有操纵条件以返回我想要的东西。我知道照应it适用于评估“何时”，但这对我来说似乎有点人为。我错过了什么吗？我成为口齿不清者才几个星期。
编辑：实际上，当我尝试应用这个时，我有点困惑。我真正想做的是：
(loop for n in '(1 2 3 4 5)
when (when (equal (mod n 2) 0) n)
collect it
do (format t "~A" it))
但第二次它似乎变得不受约束......我该怎么做？
I trying to iterate through a sequence, conditionally perform an operation on each element and then collect it (but only if it matched the criteria). Here is a simplified example that works, I just want to know if this is proper or best practice in lisp:
(loop for n in '(1 2 3 4 5)
when (when (equal (mod n 2) 0) n )
collect it)
yields
(2 4)
This works, it just looks funny to me and not so much of the when-when but because I feel like I am having to rig the condition to return what I want. I get that the anaphoric it works on the evaluation of the when but this just seems a little artificial to me. Am I missing something? I have only been a lisper for a few weeks.
Edit: Actually, I am somewhat confused when I tried to apply this. What I really want to do is this:
(loop for n in '(1 2 3 4 5)
when (when (equal (mod n 2) 0) n)
collect it
do (format t "~A" it))
but the second it seems to become unbound... how do I do this?
如果你对这篇内容有疑问，欢迎到本站社区发帖提问 参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。
绑定邮箱获取回复消息
由于您还没有绑定你的真实邮箱，如果其他用户或者作者回复了您的评论，将不能在第一时间通知您！
发布评论
评论（1）
我不明白为什么你需要这里照应词。
如果您想要无条件使用 FORMAT，请删除关键字 AND。
I don't see why you need anaphor here.
Delete the keyword AND if you want the FORMAT unconditionally.