cond_re.clj

(defn- re-clause-to-if [s [re bindings body] else]
  `(if-let [[~'_ ~@bindings] (re-find ~re ~s)]
     ~body
     ~else))

(defn- re-clauses-to-ifs [s clauses]
  (when-first [clause clauses]
              (if (and (not (next clauses))
                       (= (count clause) 1))
                (first clause)
                (re-clause-to-if s clause (re-clauses-to-ifs s (rest clauses))))))

(defmacro cond-re [s & clauses]
  (re-clauses-to-ifs s (partition 3 3 nil clauses)))

(comment ;example

(cond-re input-string
  #"([0-9]+)" [n] (format "got a number: %d" n)
  #"([0-9]+)/([0-9]+)" [num den] (format "got a ration: %d/%d" dum den)
  #"\"(.*)\"" [s] (format "got a string: %s" s))
)