I apologize about the beginner questions. I am new to Clojure.
If I do this:
(defn run-server [port what-to-do]
(let [server-socket (ServerSocket. port "localhost")]
(while (not (. server-socket isClosed))
(listen-and-respond server-socket what-to-do))))
(defn -main [& args]
(let [port (Integer/parseInt (first args))
service (symbol (second args))]
(println "Server is starting")
(println "port: " port)
(println (second args))
(println (symbol (second args)))
(println "service: " service)
(run-server port service)))
And on the command line I call it like:
java -jar who-is-logged-in-1.0-standalone.jar 3456 "who-is-here-now"
This prints out:
Server is starting
port: 3456
who-is-here-now
who-is-here-now
service: who-is-here-now
but then I get this error:
Exception in thread "main" java.lang.ClassCastException: java.lang.String
cannot be cast to java.lang.Number
at who_is_logged_in.core$run_server.invoke(core.clj:27)
Line 27 is:
(defn run-server [port what-to-do]
The only way I can read the error message is to think that the code is
trying to assign the value of what-to-do to the (integer) "port".
What have I done wrong?
On Tuesday, August 28, 2012 12:47:44 PM UTC-4, larry google groups wrote:
>
> >Command line arguments that are not strings need to be converted
> > prior to use by your main function.
>
> That makes sense, I need to cast it to a symbol, yes? I have a problem
> with that though. At the REPL I tried something like this:
>
> (def hey (resolve (symbol what-to-do)))
>
> which worked great at the REPL, but in my code I get "nil" returned from
> resolve. If I do this:
>
> (defn -main [& args]
> (let [port (Integer/parseInt (first args))
> service (resolve (symbol (second args)))]
> (println "Server is starting")
> (println "port: " port)
> (println (second args))
> (println (symbol (second args)))
> (println "service: " service)
> (run-server port service)))
>
> And call it like this:
>
> java -jar who-is-logged-in-1.0.0-SNAPSHOT-standalone.jar 3456
> "who-is-here-now"
>
> Everything looks correct till the final line when I get "nil":
>
> Server is starting
> port: 3456
> who-is-here-now
> who-is-here-now
> service: nil
>
>
>
>
>
>
>
>
> On Tuesday, August 28, 2012 6:53:24 AM UTC-4, Jon_Boone wrote:
>>
>> Command line arguments that are not strings need to be converted prior to
>> use by your main function.
>>
>> Look at the code for the port number and do the same for the service.
>>
>> --jon
>>
>>
>> On Aug 28, 2012, at 2:42, larry google groups <[email protected]>
>> wrote:
>>
>>
>> So, this started when I read Keith Swallow's article on a simple web
>> server:
>>
>> http://keithcelt.com/a-simple-web-server-in-clojure
>>
>> I took his code and ran "lein new" to create a new project and I copy and
>> pasted his code to core.clj and made some minor adjustments, adding
>> gen-class and main so I could run this from the command line. My main
>> function looked like this:
>>
>> (defn -main [& args]
>> (let [port (Integer/parseInt (first args))]
>> (println "Server is starting")
>> (run-server port echo)))
>>
>> Which called his function:
>>
>> (defn run-server [port service]
>> (let [server-socket (create-socket port)]
>> (while (not (. server-socket isClosed))
>>
>> (listen-and-respond server-socket service))))
>>
>> I compiled that and ran "lein uberjar" and then ran it from the command
>> line and it worked great.
>>
>> Then, to make it slightly more flexible, I wanted to hand in the name of
>> the service from the command line. So I made a minor change:
>>
>>
>> (defn run-server [port what-to-do]
>> (let [server-socket (ServerSocket. "localhost" port)]
>> (while (not (. server-socket isClosed))
>> (listen-and-respond server-socket what-to-do))))
>>
>> (defn -main [& args]
>> (let [port (Integer/parseInt (first args))
>> service (second args)]
>> (println "Server is starting")
>> (println "port: " port)
>> (println "service: " service)
>> (run-server port service)))
>>
>> I compiled this and ran it. And now this line:
>>
>> (defn run-server [port what-to-do]
>>
>> Gets this error:
>>
>> Exception in thread "main" java.lang.ClassCastException: java.lang.String
>> cannot be cast to java.lang.Number
>> at who_is_logged_in.core$run_server.invoke(core.clj:27)
>>
>> I'm calling it from the command line with:
>>
>> java -jar who-is-logged-in-1.0.0-SNAPSHOT-standalone.jar 3456
>> who-is-here-now
>>
>> I also tried putting the service name in quotes:
>>
>> java -jar who-is-logged-in-1.0.0-SNAPSHOT-standalone.jar 3456
>> "who-is-here-now"
>>
>> Can anyone tell me what is wrong? Why does Clojure think I'm trying to
>> cast "who-is-here-now" to a number?
>>
>>
>>
>> --
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>>
>>
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