alexpw

(let [qparams {"cat" "meow"}
      parammap {"cat" #(println "feline says" %), "dog" #(println "canine says" %)}
      foundparam (into {} (filter #(contains? parammap (key %)) qparams))]
  ((get parammap (key (first foundparam))) (val (first foundparam))))
;> feline says meow

; Cleaner?
(let [queryparams {:cat "meow", :cheese "nonsense"}
      functionmap {:cat #(println "feline says" %), :dog #(println "canine says" %)}
      selectedkey (first (select-keys functionmap (keys queryparams)))]

alexpw

(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)))
        {}