Exceptions: Unbound cannot be cast to clojure.lang.Named,compiling - exception

Question

I am trying to use clj-http/client to retrieve a web page. It looks like it is kind of working, but sometimes I receive this kind of Exception
Exception in thread "main" java.lang.ClassCastException: clojure.lang.Var$Unbound cannot be cast to clojure.lang.Named,compiling:(/tmp/form-init8570082100332402765.clj:1:72)
This is a simple function which retrieves an url from a database (from jdbc/query :row-fn), requests the contents of the url and writes it to the database. The proxy data is random and just for reference.
(defn get-source
"get content of an url"
[row]
(def my-proxy "72.159.148.20")
(def my-port 10000)
(def my-url (:url row))
(def h {"User-Agent" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/34.0"})
(try
(def my-body (:body (client/get my-url {:proxy-host my-proxy :proxy-port my-port :follow-redirects false :headers h :conn-timeout 100000})))
(catch clojure.lang.ExceptionInfo e
(prn "caught" e))
)
(write-data-to-db my-url my-body))
The value of row is coming from simple db query:
(defn -main
"I don't do a whole lot ... yet."
[& args]
(def db-spec
{
:subprotocol "mysql"
:subname "//localhost:3306/a"
:user "user"
:password "pass"})
((jdbc/query db-spec ["SELECT url FROM main where html is null and url is not null limit 2"] :row-fn get-source)))
Thanks for healthy criticism, I have fixed my example to be more correct.
(defn get-source
"get list of urls to grab in"
[row]
(let [proxy "107.161.31.220" port 8080 url (:url row)
h {"User-Agent" "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:33.0) Gecko/20100101 Firefox/34.0"}]
(:status (client/get url {:proxy-host proxy :proxy-port port :follow-redirects false :headers h :conn-timeout 100000}))))
I hope this way it much better, and I can not get that Exception any more, so could be it was buried inside that mess I came with initially.

Answer 1

I think it's not idiomatic in Clojure (or it's just not declarative) to def something inside a function or "block". Def declares global variables.
From http://clojure.org/special_forms:
(def symbol init?)
Creates and interns or locates a global var with the name of symbol and a namespace of the value of the current namespace. <...> def yields the var itself (not its value).
I guess you have to put (write-data-to-db) inside try-block and use let instead of def. Right now you're trying to access value of something that might fail.