fix-parens.clj

(use 'name.choi.joshua.fnparse)

(def tokenize (partial re-seq #"[\[\](){}]|[^\[\](){}]+"))

(defn initial-state
  [input] {:remainder (tokenize input) 
           :brackets  (list)})

(def brackets {"[" "]" "(" ")" "{" "}"})

(def opening (complex [open (term (set (keys brackets)))
                       _    (update-info :brackets (partial cons open))]
                      open))

(def closing (failpoint (term (set (vals brackets)))
                        (fn [remainder state]
                          (let [bs (:brackets state)]
                            (if (or (seq remainder) (empty? bs))
                              nil
                              [(first bs) (assoc state :brackets (rest bs))])))))

(def content (term (complement (set (flatten (seq brackets))))))

(def expression (alt (complex [open opening
                               body (rep* expression)
                               _    closing]                                
                              (str open (apply str body) (brackets open)))
                     content))

(def fix-parens (comp (partial rule-match expression prn prn)
                      initial-state))