gave defmulti defonce-like semantics, i.e. calling again won't trash …

…multifn object, to help in reload scenarios

added remove-all-methods for multifns

src/clj/clojure/core.clj

@@ -1189,14 +1189,21 @@
     (let [options   (apply hash-map options)
           default   (get options :default :default)
           hierarchy (get options :hierarchy #'global-hierarchy)]
-      `(def ~(with-meta mm-name m)
-         (new clojure.lang.MultiFn ~(name mm-name) ~dispatch-fn ~default ~hierarchy)))))
+      `(let [v# (def ~mm-name)]
+         (when-not (and (.hasRoot v#) (instance? clojure.lang.MultiFn (deref v#)))
+           (def ~(with-meta mm-name m)
+                (new clojure.lang.MultiFn ~(name mm-name) ~dispatch-fn ~default ~hierarchy)))))))
 
 (defmacro defmethod
   "Creates and installs a new method of multimethod associated with dispatch-value. "
   [multifn dispatch-val & fn-tail]
   `(. ~(with-meta multifn {:tag 'clojure.lang.MultiFn}) addMethod ~dispatch-val (fn ~@fn-tail)))
 
+(defn remove-all-methods
+  "Removes all of the methods of multimethod."
+ [#^clojure.lang.MultiFn multifn]
+ (.reset multifn))
+
 (defn remove-method
   "Removes the method of multimethod associated with dispatch-value."
  [#^clojure.lang.MultiFn multifn dispatch-val]

src/clj/clojure/core_print.clj

@@ -137,16 +137,11 @@
 
 (defmethod print-dup clojure.lang.ISeq [o w] (print-method o w))
 (defmethod print-dup clojure.lang.IPersistentList [o w] (print-method o w))
-(prefer-method print-method clojure.lang.IPersistentList clojure.lang.ISeq)
-(prefer-method print-dup clojure.lang.IPersistentList clojure.lang.ISeq)
 (prefer-method print-method clojure.lang.ISeq clojure.lang.IPersistentCollection)
 (prefer-method print-dup clojure.lang.ISeq clojure.lang.IPersistentCollection)
 (prefer-method print-method clojure.lang.ISeq java.util.Collection)
 (prefer-method print-dup clojure.lang.ISeq java.util.Collection)
 
-(defmethod print-method clojure.lang.IPersistentList [o, #^Writer w]
-  (print-meta o w)
-  (print-sequential "(" print-method " " ")" o w))
 
 
 (defmethod print-dup java.util.Collection [o, #^Writer w]

src/jvm/clojure/lang/MultiFn.java

@@ -40,6 +40,12 @@ public MultiFn(String name, IFn dispatchFn, Object defaultDispatchVal, IRef hier
 	cachedHierarchy = null;
 }
 
+synchronized public MultiFn reset(){
+	methodTable = methodCache = preferTable = PersistentHashMap.EMPTY;
+	cachedHierarchy = null;
+	return this;
+}
+
 synchronized public MultiFn addMethod(Object dispatchVal, IFn method) throws Exception{
 	methodTable = getMethodTable().assoc(dispatchVal, method);
 	resetCache();