I want to write a schema where an element e in a data structure can be any member in a set S of items; e ∈ S. With Clojure Spec this is expressed with a set like:
(spec/def ::key-set #{:subprocess :leiningen :nrepl})
(gen/sample (spec/gen ::key-set))
; => (:nrepl :subprocess :subprocess :leiningen :subprocess :nrepl :subprocess :leiningen :nrepl :subprocess)
for a set of keywords.
In Schema however a set is used to denote a set of things rather than one element member of a set. So how do I in Schema express that I want one member out of a set?
schema.core/enum is what you're looking for.
user=> (schema.core/validate (schema.core/enum "a" "b" "c") "a")
"a"
=> (schema.core/validate (schema.core/enum "a" "b" "c") "z")
clojure.lang.ExceptionInfo: Value does not match schema: (not (#{"a" "b" "c"} "z"))