...because C++ had that one good thing

cout.clj

(defmacro << [& body]
  (let [[fmt args] (loop [fmt         ""
                          args        []
                          [p & more]  body]
                     (if p
                       (cond
                         (and (symbol? p) (starts-with (name p) "%")) (recur (str fmt (name p)) (conj args (first more)) (rest more))
                         (symbol? p)                                  (recur (str fmt "%s") (conj args p) more)
                         (string? p)                                  (recur (str fmt (str p)) args more)
                         :else                                        (recur (str fmt "%s") (conj args p) more))
                       [fmt args]))]
    `(format ~fmt ~@args)))

(= (<< "hello " %s "world" ", PI is " %.2f 3.14159) (format "hello %s, PI is %.2f" "world" 3.14159))) ;=> true

(let [s  "foo"
      i  42
      f  3.14159]
  (= (<< %s s ", " %d i ", " %.2f f) (format "%s, %d, %.2f" s i f)) ;=> true
  (= (<< s ", " s) "foo, foo")             ;=> true
  (= (<< "1 + 2 = " (+ 1 2)) "1 + 2 = 3")) ;=> true