如何使用clojure进行简单的try/catch？

Question

下面的代码片段都不适用于clojure 1.6.0

(try
 (prn vv)
  (catch clojure.lang.ExceptionInfo e (prn "catch e: " e))
  (finally (prn "finally") )
)

在阅读了其他一些帖子之后我也尝试了这个:

(try
 (doall (prn vv))
  (catch clojure.lang.ExceptionInfo e (prn "catch e: " e))
  (finally (prn "finally") )
)

我错过了什么？

麦克风

Answer 1

捕获ExceptionInfo只会捕获使用ex-info创建的throwable:

(try
  (throw (ex-info "bad" {:a 1 :b 2}))
  (catch clojure.lang.ExceptionInfo e
    (prn "caught" e)))
;; => "caught" #<ExceptionInfo clojure.lang.ExceptionInfo: bad {:b 2, :a 1}>

但不是其他例外:

(try
  (/ 1 "0")
  (catch clojure.lang.ExceptionInfo e
    (prn "caught" e)))
;; => ClassCastException java.lang.String cannot be cast to java.lang.Number  clojure.lang.Numbers.divide (Numbers.java:155)

你会发现这样的:

(try
  (/ 1 "0")
  (catch Exception e
    (prn "caught" e)))
;; => "caught" #<ClassCastException java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number>

编译异常在评估之前发生:

(try
  w is undefined
  (catch Exception e
    (prn "caught" e)))
;; => CompilerException java.lang.RuntimeException: Unable to resolve symbol: w in this context, compiling:(/private/var/folders/8r/y2d3thln6s3fyrl_s6vknb440000gn/T/form-init6601588363347445596.clj:1:5) 

(try
  (eval 'w)
  (catch Exception e
    (prn "caught" e)))
;; => "caught" #<CompilerException java.lang.RuntimeException: Unable to resolve symbol: w in this context, compiling:(/private/var/folders/8r/y2d3thln6s3fyrl_s6vknb440000gn/T/form-init6601588363347445596.clj:1:5)>

您还可以使用多个catch子句来处理不同类型的异常.