4clojure problem 117 issue

p117.clj

; http://www.4clojure.com/problem/117
(fn [g]
    (let [w   (count (first g))
          h   (count g)
          xys (for [x (range w) y (range h)] [x y])
          at  (fn [[x y]] (if (and (< -1 x w) (< -1 y h)) (get-in g [y x]) \#))
          c?  (fn [[n0 n1]] (and (not= \# (at n0)) (not= \# (at n1))))
          ns  (fn [x y] 
                (for [[dx dy] [[-1 0] [1 0] [0 1] [0 -1]]] 
                  [(+ x dx) (+ y dy)]))
          es  (->> (for [[x y] xys n (ns x y)] [[x y] n]) (filter c?))
          M   (some #(if (= \M (at %)) %) xys)
          C   (some #(if (= \C (at %)) %) xys)]
      (let [all xys
          m (merge 
              (into {} (for [i all j all] [[i j] (if (= i j) 0 1)]))
              (into {} (for [p es] [p 0])))
          m (->> (for [k all i all j all] [i j k])
              (reduce
                (fn [m [i j k]]
                  (update-in m [[i j]] min (+ (m [i k]) (m [k j]))))
                m))]
        (zero? (m [M C])))))

; java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.RuntimeException: java.lang.IllegalArgumentException: Don't know how to create ISeq from: clojure.lang.Symbol