edge-cases.clj

(defn comp
  "Takes a set of functions and returns a fn that is the composition
  of those fns.  The returned fn takes a variable number of args,
  applies the rightmost of fns to the args, the next
  fn (right-to-left) to the result, etc."
  ([] identity) 
  ([fun] fun)
  ([& fs]
    (let [fs (reverse fs)]
      (fn [& args]
        (loop [ret (apply (first fs) args) fs (rest fs)]
          (if fs
            (recur ((first fs) ret) (rest fs))
            ret))))))

(defmacro ->
  "Threads the expr through the forms. Inserts x as the
  second item in the first form, making a list of it if it is not a
  list already. If there are more forms, inserts the first form as the
  second item in second form, etc."
  ([x] x)
  ([x form] (if (seq? form)
              `(~(first form) ~x ~@(rest form))
              (list form x)))
  ([x form & more] `(-> (-> ~x ~form) ~@more)))