(defn my-interleave [a b]
 "Like interleave, but uses all elements from both lists."
 (loop [acc [] a a b b]
   (if (and (nil? a) (nil? b))
     acc
     (let [acc2 (if (nil? a)
                  acc
                  (conj acc (first a)))
           acc3 (if (nil? b)
                  acc2
                  (conj acc2 (first b)))]
       (recur acc3 (rest a) (rest b))))))

;; (my-interleave [1 2 3 4 5 6 7 8] [:a :b :c :d])
;; => [1 :a 2 :b 3 :c 4 :d 5 6 7 8]

(defn read-from-string [s]
 (read (java.io.PushbackReader. (java.io.StringReader. s))))

(defn tokenize [s]
 (let [positions (let [mm (re-matcher #"\\$(?!\\\\)\\{.*?\\}" s)]
                   (loop [acc []]
                     (if (.find mm)
                       (recur (conj acc [(.start mm) (.end mm)]))
                       acc)))
       intermed (conj (apply vector 0 (apply concat positions))
                      (.length s))
       textposns (partition 2 intermed)]
   (my-interleave (map (fn [[a b]] [:text (. (.substring s a b)
                                             (replaceAll "\\$\\\\\\{" "\\${"))])
                       textposns)
                  (map (fn [[a b]] [:pat (.substring s (+ a 2) (- b 1))])
                       positions))))

;; (prn (tokenize "${greeting}, my name is ${name} and my age is ${age} $\\{a}."))
;; (. "$\\{a}" (replaceAll "\\$\\\\\\{" "\\${"))

(defmacro i [s]
 (apply list 'str
        (map (fn [[type value]]
               (if (= type :text)
                 value
                 (read-from-string value)))
             (tokenize s))))

;; test

;; (let [greeting "Hello" name "Fred" age 33]
;;  (prn (i "${greeting}, my name is ${name} and my age is ${age}.")))

;; (macroexpand '(i "${greeting}, my name is ${name} and my age is ${age}."))
;; you can get a literal ${ by using $\\{
;; (macroexpand '(i "${greeting}, my name is ${name} and my age is ${age} $\\{a}."))