2.1.bel

(def execute (pc p)
  (withs (at [(inc ((+ _ pc) p)) p]
          op [do (set (at 3) (_ (at 1) (at 2)))
                 (execute (+ pc 4) p)])
    (case (pc p)
      1 (op +)
      2 (op *)
      99 p)))

(set input (from "2.txt" (cons (read) (drain (do (rdc) (read))))))

(set (2 input) 12)
(set (3 input) 2)

(prn (1 (execute 1 input)))