This of course won't work when the body of code returns nil.
Regards,
Shantanu
On Mar 18, 8:08 pm, Shantanu Kumar <kumar.shant...@gmail.com> wrote:
> An alternate way of doing it:
>
> (defmacro maybe
> [& body]
> `(try [(do ~@body) nil]
> (catch Exception e#
> [nil e#])))
>
> (defn repeat-exec
> ([f]
> (let [run (fn g[] (cons (f) (lazy-seq (g))))]
> (run)))
> ([n f]
> (take n (repeat-exec f))))
>
> (defmacro try-times
> [n & body]
> `(let [f# #(first (maybe ~@body))
> c# (repeat-exec (dec ~n) f#)
> r# (some identity c#)]
> (or r# (do ~@body))))
>
> Putting it into action:
>
> (defn f
> "The sample function we want to try several times"
> []
> (println "x ")
> (str "y " "z ")
> (throw (NullPointerException. "boom ")))
>
> (try-times 10 (f))
>
> Hope this helps.
>
> Regards,
> Shantanu
>
> On Mar 18, 6:49 am, Fiel Cabral
>
>
>
>
>
>
>
> <e4696wyoa63emq6w3250kiw60i4...@gmail.com> wrote:
> > Hello Clojure users,
> > This is a dumb question but I'd like to write something equivalent to this
> > in Clojure:
>
> > public String loop_with_exception(int retries)
> > {
> > for (int n = retries; n > 0; n--) {
> > try {
> > return some_io_operation();
> > } catch (IOException e) {
> > continue;
> > }
> > }
> > return null;
>
> > }
>
> > So I tried writing it like this:
>
> > (ns sandbox.core
> > (:import [java.io.IOException]))
>
> > (defn some-io-operation
> > "Some read I/O operation that could throw an IOException."
> > []
> > (println "WOULD do a read operation"))
>
> > (defn loop-with-exception [retries]
> > (loop [n retries]
> > (try
> > (when (pos? n)
> > (some-io-operation))
> > (catch IOException e
> > (recur (dec n))))))
>
> > But I get this error:
>
> > cd c:/EMACSHOME/CLOJURE-PROJECTS/sandbox/src/sandbox/
> > 1 compiler notes:
>
> > Unknown location:
> > error: java.lang.UnsupportedOperationException: Cannot recur from
> > catch/finally
>
> > core.clj:13:9:
> > error: java.lang.UnsupportedOperationException: Cannot recur from
> > catch/finally (core.clj:13)
>
> > Compilation failed.
>
> > What's the recommended way to handle exceptions and retry inside a
> > loop/recur?
>
> > Thank you.
>
> > -Fiel Cab.ral
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