generators-question

generators-question.clj

(require '[clojure.spec.alpha :as s])
(require '[clojure.spec.gen.alpha :as gen])

;; I was trying to write a spec for an 5-10 character alpha string with a
;; custom generator that uses clojure.spec.gen.alpha/char-alpha
(s/def ::test
  (s/spec (s/and string? #(<= 5 (count %) 10))
          :gen (fn [] (gen/fmap #(apply str %)
                                (gen/vector gen/char-alpha 5 10)))))

;; sampling fails because clojure.spec.gen.alpha/char-alpha is not a generator
(gen/sample (s/gen ::test))
;; => Unhandled java.lang.AssertionError
;;    Assert failed: First arg to sample must be a generator (generator? generator)

;; clojure.spec.gen.alpha/char-alpha doesn't seem to pass
;; clojure.test.check.generators/generator?
(clojure.test.check.generators/generator? clojure.spec.gen.alpha/int) ;; => false
(gens/generator? gens/int) ;; => true

;; using clojure.test.check.generators/char-alpha instead seems to work
(require '[clojure.test.check.generators :as gens])

(s/def ::test (s/spec (s/and string? #(<= 5 (count %) 10))
                      :gen (fn [] (gen/fmap #(apply str %)
                                            (gen/vector gens/char-alpha 5 10)))))

(gen/sample (s/gen ::test))
;; => ("ylfWBh"
;;     "kuEIOqw"
;;     "GSdwuOOy"
;;     "sMUQFUAUyU"
;;     "nJAwjJbB"
;;     "fmNjbG"
;;     "GKTFADDaDc"
;;     "GGxblg"
;;     "KQveJyi"
;;     "EeBAy")