A simple selector

selector.clj

(defn is-predicate-keyword? [k]
  (= (last (name k)) (last "?") ))

(reduce
 (fn [acc [k v]]
   (if (is-predicate-keyword? k)
     (if (true? v)
       (conj acc (apply str (butlast (name k))))
       acc)
     acc))
 []
 {:x :value
  :x? true
  :y? false
  :z true})

;; should output ["x"]

(is-predicate-keyword? :hello)