A get-indent function to get the amount of indention for the next line of clojure code, based on the previous line.

get-indent.clj

(def closing {\) \(
              \} \{
              \] \[})
(def opening [\( \{ \[])
(defn zero-or-more [x] (if (>= x 0) x 0))
(defn indent-exception? [[a b]] (not (and (= a \') (= b \())))

; warning: Very basic clojure language parsing. It does not handle strings.
(defn reverse-parse 
  ([data] (reverse-parse data []))
  ([data starting-stack]
   (loop [pos (dec (.length data))
          stack starting-stack]
     (if (< pos 0)
         [pos stack]
         (let [cur (.charAt data pos)]
              (cond 
                   (contains? closing cur) (recur (dec pos) (conj stack (closing cur)))
                   (= (peek stack) cur) (recur (dec pos) (pop stack))
                   (some {cur true} opening) [pos stack]
                   :else (recur (dec pos) stack)))))))
 
 
(defn get-indent [data]
  (let [pos (first (reverse-parse data))]
      (if (= pos -1)
          (count (re-find #"^\s+" data)) ;match indent
          (if (indent-exception? [(.charAt data (zero-or-more (dec pos))) (.charAt data pos)])
              (let [m (re-matcher #"[,\s]+" (.substring data pos))]
                (if (.find m)
                    (+ pos (.end m))  ;match first parameter position
                    pos))
                (inc pos))))) ;match inside delimiter position
 
 
(get-indent "(defn thing [x]") ; => 6