OCaml Scanf parsing

try_parse.ml

(* I overuse these two badboys *)
let parse fmt map line = try Some (Scanf.sscanf line fmt map) with _ -> None

let rec try_parse parsers line =
  match parsers with
  | [] -> failwith ("could not parse: " ^ line)
  | parse :: parsers -> (
      match parse line with
      | None -> try_parse parsers line
      | Some result -> result
    )

(* example from AoC 2021 day 14 *)
(* see https://adventofcode.com/2021/day/14 *)
type growth = {
  opening : Char.t;
  closing : Char.t;
  value : Char.t;
}

(* we want to parse these *)
type instruction =
  | Reaction of growth
  | Polymer of string

(* data looks like this *)
(* NNCB    *)
(* CH -> B *)
(* HH -> N *)
(* CB -> H *)

(* try to parse a [Polymer], then a [Reaction] *)
(* just match these printf style strings with the function and tadaaaa *)
let parsers =
    [
      parse "%s" (fun s -> Polymer s);
      parse "%c%c -> %c" (fun opening closing value ->
          Reaction { opening; closing; value }
      );
    ]

let instructions = List.map ~f:(try_parse parsers) lines