idd.clj

;; I cant resist paste my version writing bootom-up through interactive driven devlopment ;-)
;; the origin of the puzzle is http://swizec.com/blog/functional-isnt-always-better/swizec/2591
(defn tails [xs]
  (take-while seq (iterate rest xs)))

(defn pairs [xs]
  (mapcat (fn [[x & y]] (map list (repeat x) y))
          (tails xs)))

;; some vesions in comments in the blog post

(defn pairs [xs]
 (distinct
  (for [x xs
        y xs :when (not (= x y))]
    (sort [x y]))))

;; another like mine but better

(defn pairs [xs]                                           
  (mapcat (partial map vector) (map repeat xs) (rest (tails xs))))

;; another one using clojure.contrib
(defn pairs [xs]
  (combinations xs 2))