(defn abstractFunction [op name]
  (fn [& operands]
    (assoc {}
      :evaluate (fn [values] (apply op (map #((:evaluate %) values) operands)))
      :toString (reduce str ["( " name (apply str #(:toString %) operands) " )"]))))


(defn evaluate [this vars]
  ((:evaluate this) vars))

(defn toString [this]
  (:toString this))

(defn Constant [val]
  (assoc {}
    :evaluate (constantly val)
    :toString (str val)))

(defn Variable [val]
  (assoc {}
    :evaluate (fn [variables] (variables val))
    :toString (str val)))

(def Add (abstractFunction + "+"))
(def Subtract (abstractFunction - "-"))
(def Divide (abstractFunction / "/"))
(def Multiply (abstractFunction * "*"))
(def Negate (abstractFunction - "-"))

(print (toString (Constant 10.0)))