異常未被捕獲的異種？

; 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"}

我無法弄清楚第二個expr有什麼問題。我期待它會重新打印：運行單元測試時出現異常未被捕獲的異種？

"in catch" 
"in finally"

同樣的事情：

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

應該通過。

來源

2012-08-28 wleung

NTHS是懶惰的，所以當你的REPL嘗試打印結果的功能實際運行：

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.

您可以捕獲該異常在nths或更有意義抓它，當你使用它

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，只要您不需要爲了某種其他原因而懶惰，您就可以在創建時實現結果。

來源

2012-08-28 00:49:30

有道理。我沒有想到repl會試圖評估'try'的返回值，也就是來自'（nths'（5 6 7 8 9）'（0 5））''的懶惰列表。 – wleung

我稱之爲「懶蟲」，它以很多方式咬我...... ps：在技術上，REPL只是試圖打印這個值，它是懶惰的seq導致它被評估，然後 –

(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=>

因爲地圖返回lazy-seq？

來源

2012-08-28 00:32:58

異常未被捕獲的異種？

回答

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