option in OCaml

Absence spelled Some or None — the type that killed null.

(* option makes absence explicit: Some value or None, no nulls. *)
let find_tag species =
  match species with
  | "sea star" -> Some 207
  | "anemone" -> Some 88
  | _ -> None

let report species =
  match find_tag species with
  | Some tag -> Printf.sprintf "%s wears tag %d" species tag
  | None -> species ^ " is untagged"

let () =
  print_endline (report "sea star");
  print_endline (report "limpet");
  (* The Option module maps and defaults without unwrapping. *)
  let next = find_tag "anemone" |> Option.map succ in
  Printf.printf "Next tag: %d\n" (Option.value next ~default:0)

How it works

1. Some 207 and None are the only shapes.
2. Matching forces both cases to be handled.
3. Option.map and Option.value ~default chain without unwrapping.

Keywords and builtins used here

• None
• Some
• in
• let
• match
• with

The run, in numbers

Lines

18

Characters to type

566

Tokens

109

Three-star pace

65 tpm

At the three-star pace of 65 tokens a minute, this run takes about 101 seconds.

Type this snippet

Step 2 of 3 in Pattern matching, step 9 of 29 in Language basics.

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