Clojure:try，catch 宏，它也关闭任何文件流(不是打开) [英] Clojure: try, catch macro that also closes any filestreams (not with-open)
问题描述
感谢到目前为止的所有帮助.这是我的新代码，它有效.但并不完全符合我的意愿.
我需要它来返回 java 异常(不要问我为什么).示例:
Thanks for all the help so far. This is my new code, which works. But not exactly as I would like it to.
I need it to return the java exception (don't ask me why).
Example:
(安全 (/1 0))
#<ArithmeticException java.lang.ArithmeticException: 除以零>
这就是我想要的样子.但是当我使用处理绑定等的其他代码子句时，我得到了 Clojure 异常:
(safe (/ 1 0))
#<ArithmeticException java.lang.ArithmeticException: Divide by zero>
which is how I want it to be. But when I make use of the other clauses of code that handle bindings etc, I get the Clojure exception:
(seefe [f(FileReader.(File. "C:/txtf.txt"))](. f read))
FileNotFoundException C: xtf.txt (The system cannot find the file specified) java.io.FileInputStream.open (:-2)
我可以做些什么来防止这种情况，并改为显示 Java 异常?
What can I do to prevent this, and show the Java exception instead?
(defmacro safe [bindings & code]
(if (list? bindings)
`(try
(println "line 8: try")
~bindings
(catch Throwable e# e#))
(if (= (count bindings) 0)
`(try ~code
(catch Throwable e# e#))
`(let ~(subvec bindings 0 2)
(try
(safe ~(subvec bindings 2) ~@code)
(catch Throwable e# e#)
(finally
(. ~(bindings 0) close)))))))
<小时>
旧
我正在努力完成一项作业，但没有任何辅导是不可能的.我的老师希望我们在 1 周内自学 Clojure 并完成这项作业.我班上的每个人都被困住了，我们已经讨厌老师了，lmao.
OLD
I'm trying to get an assignment done, but it's impossible without any tutoring. My teachers expect us to teach ourselves Clojure in 1 week and complete this assignment. Everyone in my class is stuck and we already hate the teacher, lmao.
好的，所以宏应该能够尝试代码，并返回结果或异常.它应该能够处理如下表达式:
Okay, so the macro is supposed to be able to try code, and return a result or an exception. It's supposed to be able to handle expressions like:
(def v (safe [s (FileReader. (File. "file.txt"))] (. s read)))
如果代码打开了任何文件流或诸如此类的东西，它应该在 finally 子句中关闭它们.这就是我到目前为止所得到的——我意识到它不起作用.
If the code opened any filestreams or whatnot, it should close them in a finally clause. This is what I got so far - I realize it's not working.
(defmacro safe [& body]
`(try ~@body
(catch Throwable e# e#)
(finally
(if (. ~@body isInstance Closable) (. ~@body close)))))
我得到的错误是:
无法解析符号:s 在此上下文中，编译:(NO_SOURCE_PATH:1)
Unable to resolve symbol: s in this context, compiling:(NO_SOURCE_PATH:1)
我绝望了，所以我尝试了很多不同的东西，我尝试了:
I got desperate so I tried alot of different stuff, I tried:
to edit the macro:
(defmacro safe [& body]
`(try ~@body
(catch Throwable e# e#)
(finally (if (. ~@body isInstance Closable) (. ~@body close)))))
然后运行:
(safe (. (java.io.FileReader. (java.io.File. "C:/Users/Dyallo.L/Dropbox/DVK11/PROP/Clojure/txt.txt")) read))
导致:
没有这样的变量:clooj.cemerick.pomegranate/Closable，编译:(NO_SOURCE_PATH:1)
No such var: clooj.cemerick.pomegranate/Closable, compiling:(NO_SOURCE_PATH:1)
有人提到了 WITH-OPEN 宏，但我想这不适用于我的通用宏.宏不是用来打开文件的，但如果是，它肯定应该关闭它们.
Someone mentioned the macro WITH-OPEN but I guess that won't work well with my generic macro. The macro isn't meant for opening files, but if they are, it should definately close them.
太糟糕了，你不会帮我一下 Stackoverflow-geniuses 吗?预先感谢.
So darn, won't you give me a hand Stackoverflow-geniuses? Thanks in beforehand.
推荐答案
with-open 宏 做同样的事情.
with-open macro does exactly the same thing.
如果有变量(可以多个)绑定到创建的对象，它会将 body 包装到 try-catch 块与 finally关闭.
If there is variable (can be more than one) bound to created object it wraps the body to try-catch block with finallyclosing.
(macroexpand-1 '(with-open [f (FileReader. (File. "1.txt"))]
(do this with f)
(do that with f)))
=>
(clojure.core/let
[f (FileReader. (File. "1.txt"))]
(try (clojure.core/with-open []
(do this with f)
(do that with f))
(finally (. f clojure.core/close))))
如果没有绑定，则只返回正文
If there are no bindings then it just returns the body
(macroexpand-1 '(with-open []
(do this with f)
(do that with f)))
=>
(do (do this with f)
(do that with f))
更新. Arthur 已经解释了您问题的例外"部分.
Update. Arthur has already explained "exception" part of your question.
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