map-cast2.clj

(defmulti  type-cast (fn [k v] k))
(defmethod type-cast :int     [k v] (Integer/parseInt v))
(defmethod type-cast :float   [k v] (Float/parseFloat v))
(defmethod type-cast :default [k v] v)

(def input {:int "1", :float ".2", :str "three" :blank ""})

(reduce (fn [xs [k v]]
          (assoc xs k (type-cast k v)))
        {}
        input)

=> {:int 1 :blank "" :str "three" :float 0.2}