在重构这个通用Lisp代码片段时，如何成功地删除包装处理程序-用例(错误处理)情况的cond子句？
在重构这个通用Lisp代码片段时，如何成功地删除包装处理程序-用例(错误处理)情况的cond子句？
提问于 2022-04-25 16:09:01
我使用的是SBCL、Emacs、Slime和Dexador ( HTTP请求的库)。我有一个函数，它可以工作
(defun old-handle-response-and-status (final-url method &optional user-content)
(let ((status-code)
(response))
(cond ((equal method "get")
(multiple-value-bind (bresponse bstatus-code)
(handler-case (dex:get final-url)
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code))))
((equal method "post")
(multiple-value-bind (bresponse bstatus-code)
(handler-case (dex:post final-url
:content user-content)
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code)))))))它适用于GET、POST，而当HTTP请求面临错误时，错误处理与预期的一样工作。显示它起作用的典型例子如下：
CL-USER> (old-handle-response-and-status "http://www.paulgraham.com" "get")
("<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01 Transitional//EN\">
<html>
(big HTML omitted)
</html>"
200)
CL-USER> (old-handle-response-and-status "https://httpbin.org/post" "post" '(("name" . "pedro")))
("{
medium JSON omitted
}
"
200)
CL-USER> (old-handle-response-and-status "https://httpstat.us/409" "get")
(NIL "The server returned a failed request of 409 status.")好的。在重构这段代码时，我试图删除cond子句。因此，我做了一个新的更短的版本：
(defun new-handle-response-and-status (method-call)
(let ((status-code)
(response))
(multiple-value-bind (bresponse bstatus-code)
(handler-case method-call
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code)))))It 主要工作，但只有在请求成功时才能工作。
CL-USER> (new-handle-response-and-status (dex:get "http://www.paulgraham.com"))
("
HTML omitted
</html>"
NIL)
CL-USER> (new-handle-response-and-status (dex:post "https://httpbin.org/post" :content '(("name" . "pedro"))))
("{
medium JSON omitted
}
"
NIL)当请求是失败的HTTP请求时，重构不像预期的那样工作！打电话时：
CL-USER> (new-handle-response-and-status (dex:get "https://httpstat.us/409"))灰泥调试器抛出：
An HTTP request to "https://httpstat.us/409" returned 409 conflict.我原以为：
(NIL "The server returned a failed request of 409 status.")我尝试将输入调整为引用的s-表达式，并插入一个eval。
(defun new-handle-response-and-status (method-call)
(let ((status-code)
(response))
(multiple-value-bind (bresponse bstatus-code)
(handler-case (eval method-call)
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code)))))它的作用是：
CL-USER> (new-handle-response-and-status '(dex:get "https://httpstat.us/409"))
(NIL "The server returned a failed request of 409 status.")但是，这感觉是一种糟糕的做法--与重构工作不完全兼容。有没有一种不使用eval来修复这个问题的方法？
也许使用funcall
回答 2
Stack Overflow用户
回答已采纳
发布于 2022-04-25 16:17:19
问题是在调用函数之前调用dex:get或dex:post，因此处理程序绑定无效。
您需要传递一个调用它的函数，然后调用该函数。
(defun new-handle-response-and-status (method-call)
(let ((status-code)
(response))
(multiple-value-bind (bresponse bstatus-code)
(handler-case (funcall method-call)
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code)))))
(new-handle-response-and-status (lambda () (dex:get "https://httpstat.us/409")))也可以将其转换为宏：
(defmacro new-handle-response-and-status (method-call)
`(let ((status-code)
(response))
(multiple-value-bind (bresponse bstatus-code)
(handler-case ,method-call
(dex:http-request-bad-request ()
(values nil
"The server returned a failed request of 400 (bad request) status."))
(dex:http-request-failed (e)
(values nil
(format nil "The server returned a failed request of ~a status." (dex:response-status e)))))
(list (setf response bresponse)
(setf status-code bstatus-code)))))Stack Overflow用户
发布于 2022-04-25 17:17:55
记住评估规则。
CL-USER 36 > (defun foo (a)
(print 'foo1)
a
(print 'foo2)
'return-value)
FOO
CL-USER 37 > (foo (print 'bar1))
BAR1
FOO1
FOO2
RETURN-VALUE(print 'bar1)在 of foo之外被评估为。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/72002527
复制相关文章
相似问题
腾讯云开发者
Copyright © 2013 - 2026 Tencent Cloud. All Rights Reserved. 腾讯云 版权所有
深圳市腾讯计算机系统有限公司 ICP备案/许可证号：粤B2-20090059 
粤公网安备44030502008569号
腾讯云计算（北京）有限责任公司 京ICP证150476号 | 京ICP备11018762号