From the Joy of Clojure, showing off the succinctness and power of Clojure.

neighbors.clj

;; Now I know what dense means :)

(defn neighbors
  ([size yx] (neighbors [[-1 0] [1 0] [0 -1] [0 1]]
                        size yx))
  ([deltas size yx]
     (filter (fn [new-yx]
               (every? #(< -1 % size) new-yx))
             (map #(vec (map + yx %))
                  deltas))))

Takes a size and a coordinate yx and returns the neighbors of that cell in a matrix. This version returns the max 4 up/down/right/left neighbors.

(neighbors 4 [0 1])
;; ([1 1] [0 0] [0 2])

For comparision, here's some code I wrote in Ruby a while back to do a similar thing: https://github.com/arnab/game_of_life/blob/master/lib/game_of_life/board.rb#L179-L188. And that doesn't reject illegal cells yet.