defratios.clj

(defmacro defratios
  "Defines two converter functions with num-expr being how many of a make up b.
For example, there are 100 centimeters in a meter.  To tell the program to make
 (centimeter->meter) and (meter->centimeter), use (defratios meter centimeters 100)"
  [a-symb b-symb num-expr]
  (and (every? #{clojure.lang.Symbol}
               (map type [a-symb b-symb]))
       (let [ab-symb (symbol (arr a-symb b-symb))
             ba-symb (symbol (arr b-symb a-symb))
             num (gensym "num-")]
         `(let [~num ~num-expr]
            ~@(for [[op arg name] [['* 'a ab-symb]
                                   ['/ 'b ba-symb]]]
                `(defn ~name [~arg] (~op ~arg ~num)))))))