slime-update-clojure-namespace-v2.el

    (defun slime-update-clojure-namespace (arg) 
      	 "Find the namespace in the current buffer and use SLIME's REPL 
to switch to it, updating the namespace for all buffers.
Using an universal prefix will ask for the name of the namespace.
The actual namespace switch is done by calling `SLIME-REPL-SET-PACKAGE'." 
      (interactive "P")
      (if arg
          (call-interactively 'slime-repl-set-package)
        (save-excursion
          ;; search for this buffer's namespace:
          (goto-char 0)
          (if (search-forward "(ns " nil t)
    	  (let* ((beg (point))
    		 (end (save-excursion
    			(forward-sexp 1)
    			(point)))
    		 (ns (filter-buffer-substring beg end)))
    	    (set-text-properties 0 (length ns) nil ns)
    	    (slime-repl-set-package ns))
    	;; no package found
    	(call-interactively 'slime-repl-set-package)))))