Modules in OCaml

Group values and types; the dot reaches inside.

(* A module groups values and types; the dot reaches inside. *)
module Tide = struct
  type phase = Ebb | Flood

  let describe = function
    | Ebb -> "falling toward the survey window"
    | Flood -> "rising, pack up the quadrats"

  let window_minutes = 90
end

let () =
  print_endline (Tide.describe Tide.Ebb);
  Printf.printf "Window: %d minutes\n" Tide.window_minutes;
  (* open brings a module's names into scope locally. *)
  let open Tide in
  print_endline (describe Flood)

How it works

1. module Tide = struct ... end bundles a type and functions.
2. Tide.describe Tide.Ebb qualifies both name and constructor.
3. let open Tide in unqualifies names for one scope.

Keywords and builtins used here

• Ebb
• Flood
• Tide
• end
• function
• in
• let
• module
• open
• struct
• type

The run, in numbers

Lines

17

Characters to type

460

Tokens

70

Three-star pace

65 tpm

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

Type this snippet

Step 1 of 2 in Modules, step 22 of 29 in Language basics.

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Modules in other languages

• Lua
• Rust