fspec_usage.clj

(s/def ::fn-takes-two-args
  (s/fspec :args (s/cat :arg1 long?
                        :arg2 long?)
           :ret long?
           :gen (fn [] (fn [a b] (* a b)))))
=> :user/fn-takes-two-args

(defn fn-that-takes-fn-with-two-args [f]
  (f 1 2))
=> #'user/fn-that-takes-fn-with-two-args

(s/fdef fn-that-takes-fn-with-two-args
  :args (s/cat :function ::fn-takes-two-args))
=> user/fn-that-takes-fn-with-two-args

(s/valid? ::fn-takes-two-args
          (fn [a b] (+ a b)))
=> true

(s/explain ::fn-takes-two-args
           (fn bad-fn [a b c] (+ a b c)))
val: (0 0) fails spec: :user/fn-takes-two-args predicate: (apply fn),  Wrong number of args (2) passed to: user/eval47132/bad-fn--47133
=> nil