introduce runonce macro

this is a helper for https://github.com/binaryage/chromex-sample/issues/10

Author: darwin

src/lib/chromex/support.clj

@@ -36,6 +36,14 @@
 (defn get-src-info [form]
   (meta form))
 
+(defmacro runonce [& body]
+  (let [code (cons 'do body)
+        code-string (pr-str code)
+        code-hash (hash code-string)
+        name (symbol (str "runonce_" code-hash))]
+    `(defonce ~name {:value ~code
+                     :code  ~code-string})))
+
 ; -- miscellaneous ----------------------------------------------------------------------------------------------------------
 
 (defn get-source-location [src-info]