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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