:3

.clj

(defn fmt [f args]
  (->> f
       (re-seq #"#\{([^\}]+)\}")
       (map (juxt (comp re-pattern #(replace % "}" "\\}") #(replace % "{" "\\{") first)
                  (comp args keyword second)))
       (reduce #(apply replace %1 %2) f)))
     
     ;; (fmt "#{foo} is a #{bar}" {:foo "foo" :bar "bar"})
     ;; => "foo is a bar"