namespace of goops module

[William Xu]

Hi people there, 

I try to learn GOOP today. As i don't want to mess with name conficts, i
decided to add a prefix while using any modules. Thus to load GOOPS, 

guile> (use-modules ((oop goops) :renamer (symbol-prefix-proc 'oop/goops:)))

This seems okay. While, when i try the first example in GOOPS Info, 

guile> (oop/goops:define-method (+ (x <string>) (y <string>))
       (string-append x y))
<unnamed port>: In expression (add-method! + (method # #)):
<unnamed port>: Unbound variable: add-method!
ABORT: (unbound-variable)

Type "(backtrace)" to get more information or "(debug)" to enter the debugger.
guile> 

Seems i can't add a renamer for goops module, but make it available on
top-level? While, GOOPS is not built in guile, is it?

So what's the point here?

-- 
William