spec.clj

; How to accomplish this so that the generator works as well?
(ns voting.core
  (:require [clojure.spec :as s]
            [clojure.spec.gen :as gen]))

(defn valid-card? [s]
  (-> (loop [n 0 s (sort s)]
        (if (empty? s) n
          (when (= (inc n) (first s)) (recur (inc n) (next s)))))
      (integer?)))
(s/def ::card (s/and 
                ;; Must contain a list of positive integers
                (s/+ (s/and integer?  #(> % 0))) 
                ;; That is a permutation of the numbers from 1 to (count card)
                valid-card?))


; true
(s/valid? ::card [3 2 1 4])

; false
(s/valid? ::card [3 2 1 5])

; ExceptionInfo Couldn't satisfy such-that predicate after 100 tries.  clojure.core/ex-info (core.clj:4617)
(gen/sample (s/gen ::card))