bad-core.clj

(ns dire-examples.bad-core
  (:require [dire.core :refer [with-precondition! with-postcondition!]]))

(defn save-user [& {:keys [username email password state]}]
  (if (and (and (> (count username) 4) (< (count username) 11))
           (and (> (count password) 6) (re-matches #".*\d.*" password))
           (re-matches #"\w+@\w+\.\w+" "[email protected]")
           (re-matches #"[A-Z]{2}" state))
    (let [result :ok] ; Or :not-ok                                                                                                                           
      "Persist the user to a database here."
      (if (not= result :ok) (throw (Throwable. "Save unsuccessful")) :ok))
    (throw (Throwable. "Something terrible has gone wrong"))))

(save-user :username "XPherior" :email "[email protected]" :password "mikemike4" :state "PA")

good-core.clj

(ns dire-examples.core
  (:require [dire.core :refer [with-precondition! with-postcondition!]]))

(defn save-user [& {:keys [username email password state]}]
  "Persist the user to a database here."
  :ok ;Or :not-ok
  )

(with-precondition! #'save-user
  :legal-username-length
  (fn [& {:keys [username]}]
    (let [length (count username)]
      (and (> length 4) (< length 11)))))

(with-precondition! #'save-user
  :well-formed-password
  (fn [& {:keys [password]}]
    (and (> (count password) 6) (re-matches #".*\d.*" password))))

(with-precondition! #'save-user
  :well-formed-email
  (fn [& {:keys [email]}]
    (re-matches #"\w+@\w+\.\w+" "[email protected]")))

(with-precondition! #'save-user
  :legal-state-abbreviation
  (fn [& {:keys [state]}]
    (re-matches #"[A-Z]{2}" state)))

(with-postcondition! #'save-user
  :successful-save
  (fn [result]
    (= result :ok)))

(save-user :username "XPherior" :email "[email protected]" :password "mikemike4" :state "PA")