forms.clj

(defn validator [param forms]
  (remove nil?
          (map (fn [[f s]] (when-not (f param) s)) forms)))

(defn- validator-wrapper [forms]
  `(fn [param#] (validator param# ~forms)))

(defn form* [forms]
  (apply merge
         (map (fn [[k v]] {k (validator-wrapper v)}) (apply array-map forms))))

(defmacro defform
  "Define a web form for validation"
  [name & forms]
  (let [validators (form* forms)]
    `(defn ~name [params#]
       (apply merge
              (map (fn [[k# v#]] {k# ((k# ~validators) v#)}) params#)))))

(defn required [param] (not (nil? param)))

(defn minimum-length [minlen]
  (fn [param] (>= (count param) minlen)))

(defform test-form
  :login [[required "Login is required"]]
  :password [[required "Password is required"]
             [(minimum-length 5) "Password should be longer than 5 chars"]])

The newest version works, the problem was with the scope of Fns. I guess.