1. Yaron Minsky
  2. core hello world


core hello world /

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Core and Async Hello World

A simple hello-world project for using Core and Async. The intent is to show you how to get started building OCaml projects using opam, core, async, and jbuilder.

We assume that you can install OCaml and opam on your platform. You'll need to install async, core, and textutils:

$ opam install async core textutils

If you're using Merlin, you also might want to pin to the latest version:

$ opam pin add merlin --dev-repo

And you should consider installing the user-setup package to set up your editor configs to use Merlin properly. This will give you interactive feedback on compilation failures, type-throwback and auto-completion.

Once that's done, you can build all the pieces of this project by running:

$ ./build_all.sh

Or you can build an individual file by calling out to jbuilder directly

$  jbuilder build hello_world.exe

There are three basic examples.

Hello World

This is a very simple exercise that shows you how to make a basic command-line application using Core's Command module.

This executable is hello_world.exe (or hello_world.bc, for bytecode), and here's an example of it in action.

core-hello-world $ ./hello_world.exe
Hello World!
core-hello-world $ ./hello_world.exe -help
Hello World


=== flags ===

  [-hello]       The 'hello' of 'hello world'
  [-world]       The 'world' of 'hello world'
  [-build-info]  print info about this build and exit
  [-version]     print the version of this build and exit
  [-help]        print this help text and exit
                 (alias: -?)

core-hello-world $ ./hello_world.exe -hello "Goodbye" -world "Yellow Brick Road"
Goodbye Yellow Brick Road!

Hello World client/server

The next example is a pair of programs: hello_server.exe and hello_client.exe. The server will accept requests via the Async.Rpc library, and the client dispatches them. The RPC is trivial: the client sends a string, and the server attaches " World!" to the end of it and sends the result back.

Message Broker

This is the most complicated example. broker_server.exe is a simple message broker that allows you to publish and subscribe to streams of data. broker_client.exe is a client that lets you do a few operations, including publishing, subscribing, getting a dump of the current state of the server, and shutting the server down.

Setting up the toplevel

You can use the built-in OCaml toplevel, ocaml, but you're probably better off using utop, which you can install via opam:

$ opam install utop

There's also a file called dot_ocamlinit, which will auto-load core and async, if you do this:

$ cp dot_ocamlinit ~/.ocamlinit

And now you can start the toplevel.

$ utop