a.clj

(ns untitled.core
  (:require [schema.core   :as s]
            [schema.macros :as sm]))

(def Length s/Int)
(def Count  s/Int)

(sm/defn add-lengths :- Length
  [a :- Length
   b :- Length]
  (+ a b))

(sm/def a-length :- Length 1)
(sm/def a-count  :- Count  2)

(sm/with-fn-validation

  (add-lengths a-length a-length) ;; okay
  (add-lengths a-length a-count) ;; <---------- I want this to crash

  )