How to Build a Simple Web Application with OCaml

Are you tired of using traditional web development tools and want to explore a new language? Do you want to build a web application with OCaml? In this tutorial, we will guide you through the process of building a simple web application with OCaml.

But why would anyone want to use OCaml for web development? Well, OCaml is a functional language with strong typing and powerful abstractions. It is a statically-typed language, which makes it easier to catch bugs early on. OCaml's performance makes it an excellent choice for building high-performance web applications.


Before we dive into the actual implementation, ensure you have the following:

If you don't have the above requirements, visit the OCaml's official website to download and install OCaml and Opam.

Setting up the Project

Now that we have all the necessary requirements let’s proceed to set up our project. To create a new project, use the following commands:

$ opam switch create project ocaml-web-app
$ eval $(opam env)

By executing the opam switch create command, you will create a new project named ocaml-web-app. The eval $(opam env) command is optional but recommended. It sets up the environment for the current session and ensures that we can use the right version of OCaml and install packages from Opam.

Once you have created the new project, create a new directory named src. This directory will hold our OCaml source code.

$ mkdir src

Next, we will install the dependencies we need. Run:

$ opam install eliom

This command installs the Eliom web framework. Eliom includes various modules that help in developing web applications with OCaml. Once we have installed Eliom, we are ready to create our first web application.

Creating our First Web Application

Now that we have all prerequisites and dependencies installed let’s get to the most exciting part of this tutorial - building our first web application with OCaml.

Head over to the src/ directory we created earlier and create a new file named

open Eliom_content.Html5.D

let main_service =
    (fun () () _ ->
            (head (title (pcdata "Welcome to my app")))
            (body [p [pcdata "Hello world"]])))
let () = Eliom_service.start ~name:"my-app" ()

In the code above, we opened the Eliom_content module, which includes various HTML modules to help us create and output HTML documents.

We then created a service that will register a new web page. In this case, we created a simple Hello world web page. We registered the service with a path of an empty list, which means that it will be the default service for our web application. We used the ~get_params option and specified the Eliom_parameter.unit type, which means that we don't need any parameters for this service.

Finally, we used the Lwt.return function to wrap our HTML output in a promise, and we used the html function to generate our HTML document.

Nothing too complex, right? Now, let's compile and start our web application. Run the following command:

$ eliom-distillery -name my_app -template basic -target-src-dir src
$ make
$ sudo make install
$ my-app.server -c /path/to/my-app.conf

By executing these commands, we compiled and installed our web application. This should launch our server, and you can access it on your web browser at http://localhost:8080.

Voila! You have successfully built a web application with OCaml.


In this tutorial, we walked you through building a simple web application with OCaml. We covered the prerequisites, setting up the project, installing dependencies and finally creating our first web application. This was just the basic of OCaml web development, and there are more powerful tools and features that OCaml offers.

If you would like to learn more about OCaml web development, check out the Eliom's official website and the various resources available on OCaml's website. Remember, always keep practicing, and happy coding!

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