gistfile1.clj

(defn infer-tag [e]
  (if-let [tag (get-tag e)]
    tag
    (case (:op e)
      :do (infer-tag (:ret e))
      :let (infer-tag (:expr e))
      :letfn (infer-tag (:expr e))
      :if (let [then-tag (infer-tag (:then e))
                else-tag (infer-tag (:else e))]
            (when (= then-tag else-tag)
              then-tag))
      :constant (case (:form e)
                  true 'boolean
                  false 'boolean
                  nil)
      nil)))