(defconst nums [4 i32] [4 8 15 16])

;; `some` unwraps Some and early-returns None from *this* function.
(defn doubled-first [s [i32]] (Option i32)
  (Some (* 2 (some (index-of s 15)))))

(defn main [] ()
  (match (doubled-first (slice nums 0 4))
    (Some i) (do (print i) (println ""))          ; 4
    None     (println "not found"))
  (match (index-of (slice nums 0 4) 99)
    (Some i) (do (print i) (println ""))
    None     (println "not found")))