Example use of the hypothetical gen/for for test.check.

gen_subset.clj

(defn gen-subset                                                                                                       
  "Generates an even-cardinality subset of the given elements"                                                                               
  [elements]                                                                                                           
  (gen/for [bools (apply gen/tuple (repeat (count elements) gen/boolean))
            :let [true-count (->> bools (filter identity) (count))]
            :when (even? true-count)]                                             
    (->> (map list bools elements)                                                                                     
         (filter first)                                                                                                
         (map second)                                                                                                  
         (set))))