(defn qmark-symbol?
  "Returns true, if sym is a symbol with name starting with a question mark."
  [sym]
  (and (symbol? sym)
       (= (first (name sym)) \?)))

(defmacro with-fresh
  "Replace all symbols with a leading question mark with fresh lvars.
  In addition, all occurences of `_' are replaced with fresh lvars, one per
  occurence.  That means, that in `forms' all occurences of ?foo will be
  unified, but all occurences of `_' are not."
  [& forms]
  (let [fs (clojure.walk/postwalk #(if (= '_ %) (gensym "?") %) forms)
        qsyms (vec (distinct (filter qmark-symbol? (flatten fs))))]
    `(fresh ~qsyms
       ~@fs)))

;; Using that, you can say something like

(run* [q]
  (with-fresh
    (foo ?x ?p _)
    (bar _ ?x ?p)))