catch
The exprs are evaluated and, if no exceptions occur, the value of the last is returned. If an exception occurs and catch clauses are provided, each is examined in turn and the first for which the thrown exception is an instance of the named class is considered a matching catch clause. If there is a matching catch clause, its exprs are evaluated in a context in which name is bound to the thrown exception, and the value of the last is the return value of the function. If there is no matching catch clause, the exception propagates out of the function. Before returning, normally or abnormally, any finally exprs will be evaluated for their side effects. See http://clojure.org/special_forms for more information.
© Rich Hickey. All rights reserved. Eclipse Public License 1.0
3 Examples
=> (try (/ 1 0) (catch Exception e (str "caught exception: " (.getMessage e)))) "caught exception: Divide by zero"
;; multiple catch clauses which handle different exceptions => (let [divisor [2 0 "clojure"]] (try (/ 4 (rand-nth divisor)) (catch ArithmeticException e (println "Probably trying to divide by zero...") 111) (catch ClassCastException e (println "Did you try to do math with a string?") 222) (catch AssertionError e (println "Some conditions aren't compatible with the requirements of a function") 333) (catch Exception e (println "Some other exception, won't be caught in this case...") 444) (finally (println "Always executed but won't return a value!")))) ;; first case Always executed but won't return a value! => 2 ;; second case Probably trying to divide by zero... Always executed but won't return a value! => 111 ;; third case Did you try to do math with a string? Always executed but won't return a value! => 222 ;; forth case Some conditions aren't compatible with the requirements of a function Always executed but won't return a value! => 333 ;; fifth case Some other exception, won't be caught in this case... Always executed but won't return a value! => 444
;; Note that in ClojureScript, one can use (catch :default e ...) to catch any ;; type of value, roughly equivalent to (catch Exception e ...) in JVM Clojure. (try (/ 2 (rand-nth [0 "oops"])) (catch :default e ; Note: ClojureScript only! (println "Error!" e))) ;; This is not currently possible in JVM Clojure, though the ticket CLJ-1293 ;; proposes adding the same behavior there and has some background info.