timezone's Introduction

Timezone for OCaml

Timezone handles parsing timezone data and create [Timezone.t] that can later be used to manipulate time in core (using [Time] and [Time_ns] modules).

Timezone is currently only able to read the Timezone Database provided by IANA. It should work out of the box on Linux and macOS.

Where are the timezone data located ?

The location of the timezone files can be set using the environment variable TZDIR. If not set, [Timezone] will fallback to /usr/share/zoneinfo/.

What is the local timezone ?

The local timezone can be set using the environment variable TZ. If not set, [Timezone] will fallback to /etc/localtime. In a JavaScript context, we automatically set the environment variable TZ to Intl.DateTimeFormat().resolvedOptions().timeZone.

Compatibility with JavaScript.

The [Timezone] library can be used when constructing JavaScript applications with Js_of_ocaml.

Node.js

[Timezone] should work out of the box when running on a Node.js environment on Linux or macOS. The file-system is accessible in that case.

Web browsers

In a web browser environment, the [Timezone] library requires some additional setup. One should generate a JavaScript file that will embed all timezone data required by the application. This can be done by using a tool provided by js_of_ocaml called jsoo_fs. The generated JavaScript file will have to be included in the HTML page before the JavaScript program itself.

For example, one can embed all timezones in all-tz.js with the following command:

grep -r TZif /usr/share/zoneinfo -l | xargs -n 1 -I {} echo {}:{} | xargs jsoo_fs -o all-tz.js

Alternatively, follow the instructions on timezone-web to use the hosted copy of the entire timezone database.

Example

open Core

let now = Time_ns.now ()

let () =
  Time_ns.to_sec_string now ~zone:(Lazy.force (Timezone.local))
  |> print_endline

let () =
  Time_ns.to_sec_string now ~zone:(Timezone.find_exn "America/New_York")
  |> print_endline