(defmacro defbinop [op zero]
  `(do
     (defmulti ~op nary-dispatch)
     (defmethod ~op ::nullary [] ~zero)
     (defmethod ~op ::n-ary
       [~'x ~'y & ~'more]
       (if ~'more
         (recur (~op ~'x ~'y) (first ~'more) (next ~'more))
         (~op ~'x ~'y)))
     (defmethod ~op [:j-long :j-long]
       [~'x ~'y]
       (clojure.core/~op ~'x ~'y))))