What is OCaml Batteries Included?

Twenty years ago, a language was just a compiler. You could measure the quality of a language from the beauty of its semantics, the clarity of its syntax, the speed of generated code. That was then. In the meantime, the Java and .Net nuclear plants have been built, while the Python and Ruby communities have gradually developed their own powerhouses. All these platforms have amply demonstrated that a language can only be as beautiful, clear and fast as the libraries which developers are actually going to use for their work. In other words, it's not about the language anymore, it's about the platform.

At this point in time, out-of-the-box, OCaml isn't a usable platform. There is no Unicode, there are no modern user interface toolkits, no distributed programming infrastructures, no network services, no type-safe communications, no analysis of other languages, no interfacing with industrial platforms, no XML, non modern two- or three-dimensional drawing engine, etc. This would not be too much of a problem if OCaml provided an easy way of installing new libraries and of using these libraries once they are installed. This would also not be too much of a problem if OCaml could somehow guarantee that trivial data structures didn't need to be reinvented by most projects and that communication between libraries happened flawlessly.

So no, out of the box, OCaml isn't a usable platform. However, no matter what you're trying to do, chances are that the community has already developed or adapted a tool to make your life easier. Easy installation of OCaml packages is quite possible, if you are using Debian or Ubuntu (apt-get), Fedora or Red Hat (yum) or actually, any Unix-compatible platform, including MacOS X and Windows (GODI). Simple and reliable usage of installed libraries can be done with Findlib. A comprehensive Unicode library is available (Camomile), as well as a modern user interface toolkit or two (LablGtk, OCamlRT), a number of distributed programming infrastructures (OCamlMPI, BSML, Opis, Camlp3l, OCamlNAE), libraries to interface with industrial platforms (OCamlJava, SpiderCaml, ...), to analyse other languages (CIL, Dalton/FlowCaml, ...), to read or write XML (PXP, Expat, ...), to draw in two or three dimensions (Cairo, OpenGL), to test your programs (OUnit), etc. OCaml even offers a built-in tool to customize the language itself (Camlp4).

What's missing? A few things. For now, not all important libraries are available as simple-to-install packages. That problem is being addressed by the devoted packagers of Debian, Fedora and GODI, while the possibility exists that the recently announced Symbiosis will also help address the issue. The other missing part is a standard set of libraries, language extensions and data structures which developers could be assured to find on every OCaml installation, and which would let them write programs without having to endlessly reinvent the same basic wheels, and without spending their time writing adapters between libraries which should work well together but don't use the same conventions. OCaml Batteries is one possible answer to this problem

OCaml Batteries Included consists in

(Batteries courtesy of Benjamin Pavie, Camel courtesy of John Olsen, no animals injured)

OCaml Batteries Included depends on other packages. We are doing our best to avoid forking any project.

It is also a project maintained by the community, which means that it depends on you. If you have ideas, suggestions, complaints, bug reports, if you want to participate, to write code, documentation, tutorials, build tools, review code, have a word in policies, if you want a package to be included in the Batteries, or just to contact us, please use our website. We provide bug trackers, request for features trackers, forums, etc. (courtesy of OCaml Core). We can also often be seen on irc, on server freenode, channel #ocaml.

OCaml Batteries Included is also a work-in-progress. The version you have in front of your eyes does not contain everything we want to put in it, nor even all the code we have written for it. But we'll get there. We intend to integrate additional libraries progressively, from minor release to minor release, with major milestones approximately twice per year. This policy is not written in stone and is largely subject to debate, so don't hesitate to comment on the subject.

For more informations on the contents of OCaml Batteries Included, follow us towards the manual.

Relations to other libraries

Project Gallium's Base Library

First, a word on vocabulary. We call "Base library" the library provided by INRIA with the default distribution of OCaml. We don't call it "standard library" for the simple reason that there are several libraries vying for the status of standard, including Batteries Included.

The relation between Batteries Included and the Base Library is simple: the Base Library is one of the libraries for which Batteries Included provides a uniformization layer. We are not forking the library, merely providing additional functions, additional documentation, boilerplate code...

The complete Base Library is available in Batteries Included as module Legacy. Most modules are also available inside the Batteries module hierarchy, sometimes under different names, and usually completed by numerous new functions. A few modules are considered obsolete and appear only in Legacy.

Jane Street's Core

Jane Street's Core is another library vying for the status of standard, this time produced by Jane Street Capital. This library is comparable in purpose and design to the core of Batteries Included (actually, we draw some inspiration from them and we hope that they are going to draw some inspiration from us, too) but there is no code shared between Batteries Included and Jane Street's Core for the moment.

In the future, Batteries Included may depend on Jane Street's Core. This is not the case yet as, according to one of Jane Street's Core's authors, this library may change quite a lot, and in what we interpret as possibly incompatible ways, before reaching version 1.0.

We already depend on two components of Jane Street's Core: Type-Conv (a general infrastructure which may be used to generate Boilerplate code) and Sexplib (an instance of Type-Conv used to generate code for serializating to/deserializing from human-readable S-Expressions). We intend to extend this to a third component of Jane Street's Core: Bin-Prot, another instance of Type-Conv, used this time to generate serialization to/from binary protocols.


ExtLib is another extension of the OCaml Base Library. ExtLib was designed as a relatively small addition, with the idea of fitting nicely within the OCaml Base Library. Since 2005, ExtLib has essentially stopped growing, following a conscious choice from the maintainers.

OCaml Batteries Included is largely based on ExtLib. Indeed, the core of Batteries is essentially a fork of ExtLib. We intend to maintain ascending compatibility with ExtLib (with the exception of changes in module names), although we have added a great number of features, fixed bugs, split code, etc. For most purposes, OCaml Batteries Included contains ExtLib and, in our mind, superseeds this library. We hope that the maintainers and developers of ExtLib will consider migrating to OCaml Batteries Included.

Community OCaml

Community OCaml is an attempt to turn OCaml into an out-of-the-box complete development platform, including numerous libraries.

We have joined forces with the developers of Community OCaml and we share most of our code. Although the design of Community OCaml is not completely decided yet, it is quite possible that this will be a distribution consisting in OCaml + Batteries Included + some package manager.


OCamlNet is an implementation of numerous Internet protocols for OCaml, along with so many utilities that it almost consists in a complete general-purpose development library for OCaml.

OCaml Batteries Included will depend on OCamlNet and incorporate OCamlNet into its hierarchy. In particular, for the moment, OCaml Batteries Included provides little in the way of libraries for interacting with the operating system, as we intend to use OCamlNet for that purpose.

Caml Development Kit

The Caml Development Kit, or CDK, was another attempt to build a development platform around OCaml by bundling together OCaml itself and a number of interesting libraries and tools. By opposition to Batteries Included, this was a monolithic distribution, with a custom compiler and very little documentation. Development on CDK seems to have died around 2001.

There is no relation between CDK and Batteries Included other than the common goal. We do our best to benefit from the experience gathered by the CDK developers. In particular, this means that we work together with package managers without attempting to provide a complete distribution.

GODI, Apt, Yum

GODI, Apt and Yum are the three main package managers available for OCaml users. The first one is OCaml-specific, the second one lives in Debian/Ubuntu/Knoppix world and the third one in the Red Hat/Fedora world.

OCaml Batteries Included has no direct relation with either package manager, nor does it replicate the work of any of these managers. However, as Batteries relies on numerous external libraries, use of a package manager is strongly recommended.


Findlib is a compile-time package manager for OCaml. It lets developers easily specify which libraries are required and manages compile-time dependencies between installed libraries.

OCaml Batteries Included uses Findlib extensively.

Comparable projects, somewhere else

Python Batteries Included

To the best of our knowledge, the term "Batteries Included" was first coined by the Python community to describe the standard distribution of Python, which in addition to usual data structures, contains modules for handling databases, compression, a number of file format (de)coders including JSON, (X)HTML, XML, CSV, cryptography, logging, text interfaces, threading, inter-process communication, implementation of client and server protocols from SMTP to HTTP, communication with external webbrowsers, image and sound manipulation, internationalization, lexing and parsing, graphical interfaces, unit testing, sandboxing, reflexivity, OS-specific services, ... This massive number of out-of-the-box features, along with the conciseness of the language, are probably the two main reasons of the success of Python: simple tasks, even those which require complex libraries, may often be programmed with only a few lines and in a few minutes.

Well, obviously, we're trying to provide something as useful with OCaml Batteries Included, but with the added safety and speed of OCaml.

Haskell Batteries Included

The Haskell Platform (also known as "Haskell Batteries Included") is a recent project undertaken by the Haskell community with objectives comparable to OCaml Batteries Included: "provides a comprehensive, stable and quality tested base for Haskell projects to work from." At the time of this writing, the Haskell Platform has not released any software, although a first release is expected within a few weeks.

As OCaml Batteries, the Haskell Platform is community-led and relies on a number of decentralized libraries. As OCaml Batteries, the Haskell Platform requires package management. There are a number of differences in the methods, though.

Some differences are probably trivial: where we strive to work with any of the major package management systems, the Haskell Platform is based solely on Cabal, which may allow them a better integration. Where OCaml Batteries attempts to reclassify existing libraries into one uniform hierarchy of modules, the Haskell Platform keeps the original module names, as decided by their original authors, pre-Platform.

Others are quite far-reaching: OCaml Batteries provides an extended core of libraries to serve as support for standardization and uniformization, while the Haskell Platform doesn't. Similarly, the Haskell Platform doesn't add any uniformization layer, which means that the task of getting libraries to work together lies upon the end-user. Some Haskell libraries may be patched into compliance and uniformization, but this is not always possible, short of creating cyclic dependencies between libraries which should work together but don't. Finally, the Haskell Platform has much stricter guidelines regarding libraries which can or can't make it into the Platform. This is a good thing if library authors are willing to fix whichever problems prevent the inclusion of their work -- something which we don't assume for OCaml Batteries, at least not yet.

Despite these differences, both projects seem based on solid foundations. And hopefully, both will achieve large success.