user=> (check "{([]){()}}")
a-string: {([]){()}}
so-far: 
a-string: ([]){()}}
so-far: {
a-string: []){()}}
so-far: {(
a-string: ]){()}}
so-far: {([
a-string: ){()}}
so-far: {(
a-string: {()}}
so-far: {
a-string: ()}}
so-far: {{
a-string: )}}	;; The parenthesis was supposed to go at the very end.
so-far: ({{
false

;; code
(defn check [a-string]
  (loop [so-far []
         a-string (seq a-string)]
    (println (str "a-string: " (apply str a-string)
                  "\nso-far: " (apply str so-far)))
    (if (and (empty? a-string) (empty? so-far)) 
      true
      (case (first a-string)
        \( (recur (conj so-far \()
                  (rest a-string))
        \{ (recur (conj so-far \{)
                   (rest a-string))
        \[ (recur (conj so-far \[)
                  (rest a-string))
        \) (if (= (last so-far) \()
             (recur (drop-last so-far)
                    (rest a-string))
             false)
        \} (if (= (last so-far) \{)
             (recur (drop-last so-far)
                     (rest a-string))
             false)
        \] (if (= (last so-far) \[)
             (recur (drop-last so-far)
                     (rest a-string))
             false)
        (if (and (empty? (rest a-string)) 
                 (complement (empty? so-far)))
          false
          (recur so-far (rest a-string)))))))