A factory defining macro.

factory.clj

(defmacro deffactory
  "Defines a factory function that returns an instance of the specified
   record initialized with the default values provided overridden by the
   values it is given."
  [factory-name record-name defaults]
  `(defn ~factory-name
     ~(str "A factory function returning a new instance of " record-name
           " initialized with the defaults specified at the time of"
           " definition overridden by the given values. The values can"
           " be specified as a map or field-value pairs.")
     ([] (~factory-name {}))
     ([~'field-value-map]
        (merge (new ~record-name ~@defaults)
               ~'field-value-map))
     ([~'field ~'value & ~'field-value-pairs]
        (~factory-name (apply hash-map ~'field ~'value
                              ~'field-value-pairs)))))