gistfile1.clj

(defmacro defmixfix [name args & body]
  (let [kws (vec (filter keyword? args))
        filter-indices (fn [pred coll]
                         (filter (complement nil?) (map-indexed #(if (pred %2) %1 nil) coll)))
        positions (vec (filter-indices keyword? args))
        genkwsym (fn [kw] (with-meta (gensym) {:name kw}))
        kw-symbols (reduce #(assoc %1 %2 (genkwsym %2)) {} kws)
        args-with-symbols (vec (map #(if (keyword? %) (% kw-symbols) %) args))]
    `(defn ~name ~args-with-symbols
       (do
         (assert (= ~kws ((comp reverse vals) (select-keys ~args-with-symbols ~positions))))
         ~@body))))

(comment
  (defmixfix ifm [e :then t :else f]
    (if e t f))

  (ifm true :then 1 :else 0)
  (ifm true :asdf 1 :qwerty 0) ; throws AssertionError
  )