Eliom 6.0: mobile and Web apps in OCaml
Written by The Ocsigen Team on December 12, 2016

We are very happy to announce the release of Ocsigen Eliom 6.0, which follows the recent releases of Ocsigen Server 2.8 and Ocsigen Js_of_ocaml 2.8.x.

New features include a friendlier service API that retains the expressive power of our service system. Additionally, Eliom can now be used to build cross-platform Web/mobile applications (Android, iOS, …).

What is Eliom?

Eliom is a framework for developing client/server web applications. Both the server and the client parts of the application are written in OCaml, as a single program. Communication between server and client is straightforward, e.g., one can just call a server-side function from client-side code.

Eliom makes extensive use of the OCaml language features. It provides advanced functionality like a powerful session mechanism and support for functional reactive Web pages.

Friendly service APIs

Services are a key concept in Eliom, used for building the pages that are sent to the user, for accessing server-side data, for performing various actions, and so on. Eliom 6.0 provides a friendlier API for defining and registering services, thus making Eliom more approachable.

The new API makes extensive use of OCaml’s GADTs, and provides a single entry-point that supports most kinds of services (Eliom_service.create). For more information, refer to the Eliom manual.

Mobile applications

Eliom 6.0 allows one to build applications for multiple mobile platforms (including iOS, Android, and Windows) with the same codebase as for a Web application, and following standard Eliom idioms.

To achieve this, we have made available the Eliom service APIs on the client. Thus, the user interface can be produced directly on the mobile device, with remote calls only when absolutely necessary.

To build an Eliom 6.0 mobile application easily, we recommend that you use our soon-to-be-released Ocsigen Start project, which provides a mobile-ready template application (walkthrough).


Eliom 6.0 supports the last 3 major versions of OCaml (4.02 up to 4.04). Additionally, Eliom is compatible with and builds on the latest Ocsigen releases, including Ocsigen Server 2.8, Js_of_ocaml 2.8.x, and TyXML 4.0.x.


The Ocsigen team is busy working on new features. Notably, we are developing an OCaml compiler specifically tuned for Eliom. Additionally, we are planning a transition to the Cohttp HTTP backend.