Hi Marc,
note that the return of gen/sample is 10 examples. Each one is a
collection.
So the collection [] matches your spec, as does [:c]. And so on.
A regex-op outside of a regex-op always specs a collection. If used within
another regex-op, it just specs an element.
To illustrate:
(gen/sample (s/gen (s/cat :kw (s/? #{:a :b :c :d})) :num number?))
((-2.0) (:a -3.0) (0) (1) (-2.625) (:a -1) (:d -1.5625) (0.75) (:a -24) (:d
-22))
Kind regards,
Leon.
On Saturday, January 28, 2017 at 6:29:39 PM UTC+1, Marc Wilhelm Küster
wrote:
>
> Good afternoon,
>
> like obviously quite a few others on this list I am looking into the
> upcoming (and IMHO absolutely great) clojure.spec
> During this I noted that the ? macro seems to behave differently from
> what I would have naively expected from its documentation (cf.
> https://clojure.github.io/clojure/branch-master/clojure.spec-api.html#clojure.spec/?
> ):
>
> ? macro
>
> Usage: (? pred-form)
>
> Returns a regex op that matches zero or one value matching
> pred. Produces a single value (not a collection) if matched.
>
>
> In contract, with the namespaces set to
> [clojure.spec :as s]
> [clojure.spec.gen :as gen]
>
> the following snippet
>
> (s/def ::abcd #{:a :b :c :d})
> (gen/sample (s/gen (s/? ::abcd)))
>
> returns a collection of collections:
> ([] [:c] [:d] [:b] [:b] [] [:a] [] [:d] [])
>
> I would have expected to find either the value itself or nothing, a
> behaviour that would seem to me also more practical when composing larger
> records with optional elements. However, I might be misreading the
> documentation and would be grateful for any clarification
>
> Best regards,
>
> Marc
>
>
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