(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-i32 s 15)))))

(defn main []
  (match (doubled-first (slice nums 0 4))
    (Some i) (do (print-i64 (i64 i)) (newline))   ; 4
    None     (print-line "not found"))
  (match (index-of-i32 (slice nums 0 4) 99)
    (Some i) (do (print-i64 (i64 i)) (newline))
    None     (print-line "not found")))