异常未被捕获的异种？

; common/math.clj 
(defn nths 
    "Returns a collection of values for each idx in idxs. Throws an error if any one idx is out of bounds." 
    [coll idxs] 
    (map #(nth coll %) idxs)) 

; nrepl 
common.math> (try (/ 1 0) 
    (catch Exception e (prn "in catch")) 
    (finally (prn "in finally"))) 
"in catch" 
"in finally" 
nil 
common.math> (try (nths '(5 6 7 8 9) '(0 5)) 
    (catch Exception e (prn "in catch")) 
    (finally (prn "in finally"))) 
"in finally" 
IndexOutOfBoundsException clojure.lang.RT.nthFrom (RT.java:784) 
common.math> (nths '(5 6 7 8 9) '(0 1 3)) 
(5 6 8) 
common.math> *clojure-version* 
{:major 1, :minor 5, :incremental 0, :qualifier "alpha4"}

我无法弄清楚第二个expr有什么问题。我期待它会重新打印：运行单元测试时出现异常未被捕获的异种？

"in catch" 
"in finally"

同样的事情：

lein test unittest.common.math 

FAIL in (test-nths) (math.clj:87) 
expected: (thrown? IndexOutOfBoundsException (nths (quote (5 6 7 8 9)) (quote (0 5)))) 
    actual: nil

应该通过。

来源

2012-08-28 wleung

NTHS是懒惰的，所以当你的REPL尝试打印结果的功能实际运行：

core> (def result (try (nths '(5 6 7 8 9) '(0 5)) 
         (catch Exception e (prn "in catch")) 
         (finally (prn "in finally")))) 
"in finally" 
#'core/result 
core> result 
; Evaluation aborted.

您可以捕获该异常在nths或更有意义抓它，当你使用它

rsadl.core> (def result (try (nths '(5 6 7 8 9) '(0 5)) 
         (catch Exception e (prn "in catch")) 
         (finally (prn "in finally")))) 
"in finally" 
#'core/result 
core> (try (println result) (catch Exception e (prn "in catch"))) 
("in catch" 
nil

或number23_cn指出，只要您不需要为了某种其他原因而懒惰，您就可以在创建时实现结果。

来源

2012-08-28 00:49:30

有道理。我没有想到repl会试图评估'try'的返回值，也就是来自'（nths'（5 6 7 8 9）'（0 5））''的懒惰列表。 – wleung

我称之为“懒虫”，它以很多方式咬我...... ps：在技术上，REPL只是试图打印这个值，它是懒惰的seq导致它被评估，然后 –

(try (doall (nths '(5 6 7 8 9) '(0 5))) 
    (catch Exception e (prn "in catch")) 
    (finally (prn "in finally"))) 
"in catch" 
"in finally" 
nil 
user=>

因为地图返回lazy-seq？

来源

2012-08-28 00:32:58

异常未被捕获的异种？

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