gistfile1.txt

 (defn rect [wd ht] {:Shape ::rect :wd wd :ht ht})
 (defn circle [radius] {:Shape ::circle :radius radius})
 (defn square [wd ht ] {:Shape ::square :wd wd :ht ht})
 
 (defmethod area :default [x] :oops)
 (defmethod area ::rect [r]
    (* (:wd r) (:ht r)))
    
 (derive ::square ::rect)
 (area (rect 10 10))
 (area (square 10 10))