From the OCaml Labs wiki
Jump to: navigation, search


News Archives[edit]

There has been lots of activity since OCaml Labs started in 2012!


The OCaml Labs initiative within the Computer Laboratory is now just over two years old, and it is time for an update about our activities since the last update at the end of 2013 and 2012.

The theme of our group was not to be pure research, but rather a hybrid group that takes on some of the load of day-to-day OCaml maintenance from INRIA, as well as help grow the wider community and meet our own research agendas around topics such as unikernels. To this end, all of our projects have been highly collaborative, often involving colleagues from OCamlPro, INRIA, Jane Street, Lexifi and Citrix.

This post covers our progress in tooling, the compiler and language, community efforts, research projects and concludes with our priorities for 2015.


At the start of 2014, we had just helped to release OPAM 1.1.1 with our colleagues at OCamlPro, and serious OCaml users had just started moving over to using it.

Our overall goal at OCaml Labs is to deliver a modular set of of development tools around OCaml that we dub the OCaml Platform. The remainder of 2014 was thus spent polishing this nascent OPAM release into a solid base (both as a command-line tool and as a library) that we could use as the basis for documentation, testing and build infrastructure, all the while making sure that bigger OCaml projects continued to migrate over to it. Things have been busy; here are the highlights of this effort.


The central OPAM repository that contains the package descriptions has grown tremendously in 2014, with over 280 contributors committing almost 10000 changesets across 3800 pull requests on GitHub. The front line of incoming testing has been continuous integration by the wonderful Travis CI, who also granted us access to their experimental MacOS X build pool. The OPAM package team also to expanded to give David Sheets, Jeremy Yallop, Peter Zotov and Damien Doligez commit rights, and they have all been busily triaging new packages as they come in.

Several large projects such as Xapi, Ocsigen and our own MirageOS switched over to using OPAM for day-to-day development, as well as prolific individual developers such as Daniel Buenzli and Markus Mottl. Jane Street continued to send regular monthly updates of their Core/Async suite, and releases appeared from the Facebook open-source team as well (who develop Hack, Flow and Pfff in OCaml).

We used feedback from the users to smooth away many of the rough edges, with:

- a redesigned development workflow that lets developers quickly grab a development version of a library recompile all dependent packages automatically, and quickly publish results to GitHub.

- binary distributions for common OS distributions via their native packaging, as well as 0install and Vagrant boxes.

- a unified way of cloning the source of any package via opam source. This handles any supported OPAM archive, including Git, Mercurial or Darcs remotes.

- a richer package metadata, including source code, development archives and bug report URLs.

These changes were all incorporated into the OPAM 1.2, along with backwards compatibility shims to keep the old 1.1 metadata format working until the migration is complete. The 1.2.x series has been a solid and usable development manager, and last week's release of OPAM 1.2.1 has further polished the core scripting engine.

Platform Blog[edit]

One of the more notable developments during 2014 was the adoption of OPAM further up the ecosystem by the Coq theorem prover. This broadening of the community prompted us to create an official OPAM blog to give us a central place for new and tips, and we've had posts about XenServer developments, the Merlin IDE tool and the modern UTop interactive REPL. If you are using OPAM in an interesting or production capacity, please do get in touch so that we can work with you to write about it for the wider community.

The goal of the blog is also to start bringing together the various components that form the OCaml Platform. These are designed to be modular tools (so that you can pick and choose which ones are necessary for your particular use of OCaml). There are more details available from the OCaml Workshop presentation at ICFP 2014 (abstract, slides, video).

Onboarding New Users[edit]

OPAM has also been adopted now by several big universities (including us at Cambridge!) for undergraduate and graduate Computer Science courses. The demands increased for an out-of-the-box solution that makes it as easy possible for new users to get started with minimum hassle. We created a dedicated teaching list to aid collaboration, and a list of teaching resources on and supported several initiatives in collaboration with [ Louis Gesbert at OCamlPro, as usual with OPAM development).

The easiest way to make things "just work" are via regular binary builds of the latest releases of OCaml and OPAM on Debian, Ubuntu, CentOS and Fedora, via Ubuntu PPAs and the OpenSUSE Build Service repositories. Our industrial collaborators from Citrix, Jon Ludlam and Dave Scott began an upstreaming initiative to Fedora and sponsored the creation of a CentOS SIG to ensure that binary packages remain up-to-date. We also contribute to the hardworking packagers on MacOS X, Debian, FreeBSD, NetBSD and OpenBSD where possible as well to ensure that binary builds are well rounded out. Richard Mortier also assembled Vagrant boxes that contain OCaml, for use with VirtualBox.

Within OPAM itself, we applied polish to the handling of external dependencies to automate checking that the system libraries required by OPAM are present. Two emerging tools that should help further in 2015 are the opam-user-setup and OPAM-in-a-box plugins that automate first-time configuration. These last two are primarily developed at OCamlPro, with design input and support from OCaml Labs.

We do have a lot of work left to do with making the new user experience really seamless, and help is very welcome from anyone who is interested. It often helps to get the perspective of a newcomer to find out where the stumbling blocks are, and we value any such advice. Just mail with your thoughts, or create an issue on how we can improve. A particularly good example of such an initiative was started by Jordan Walke, who prototyped CommonML with a NodeJS-style development workflow, and wrote up his design document for the mailing list. (Your questions or ideas do not need to be as well developed as Jordan's prototype!)

Testing Packages[edit]

The public Travis CI testing does come with some limitations, since it only checks that the latest package sets install, but not if any transitive dependencies fail due to interface changes. It also doesn't test all the optional dependency combinations due to the 50 minute time limit.

We expanded the OPAM repository testing in several ways to get around this:

  • Individual Repositories: Thomas Gazagnaire built centralised Travis scripts that can be used on any OCaml GitHub repository to easily test code before it is released into OPAM. These scripts are sourced from a central repository and support external, optional and reverse dependency checking across multiple revisions of the compiler. For instance, it just needs cohttp/blob/master/.travis.yml one file to test all the supported permutations of the CoHTTP library.
  • Bulk Builds: Damien Doligez and I independently started doing large-scale bulk builds of the repository to ensure that a single snapshot of the package repository can automatically build as many packages as possible. My implementation used the Docker container manager to spawn off 1000s of package builds in parallel and commit the results into a filesystem. This required building a Dockerfile eDSL, and the results are now online at [1] builds.
  • OCamlot: An ongoing piece of infrastructure work is to take the bulk build logs (which are around 7GB per daily run), and to store and render them using our Irmin Git store. Expect to see more around this soon; it has the awesome feature of letting any developer clone the build logs for their project locally, to make triage of foreign operating systems as simple as possible.

Language Evolution[edit]

This ability to do unattended builds of the package repository has also improved the decision making process within the core compiler team. Since we now have a large (3000+ package) corpus of OCaml code, it became a regular occurrence in the 4.02 development cycle to "ask OPAM" whether a particular feature or new syntax would break any existing code. This in turn provides an incentive for commercial users to provide representative samples of their code; for instance, the Jane Street Core releases in OPAM (with their very modular style) act as an open-source canary without needing access to any closed source code.

One good example in 2014 was the decoupling of the Camlp4 macro preprocessor from the main OCaml distribution. Since Camlp4 has been used for over a decade and there are some very commonly used syntax extensions such as type_conv, a simple removal would break a lot of packages. We used OPAM to perform a gradual movement that most users hopefully never noticed by the time OCaml 4.02 was released. First, we added a dummy package in OPAM for earlier versions of the compiler that had Camlp4 built-in, and then used the OPAM constraint engine to compile it as an external tool for the newer compiler revisions. Then we just had to triage the bulk build logs to find build failures from packages that were missing a Camlp4 dependency, and add them to the package metadata.

GitHub Integration[edit]

An interesting comment from Vincent Hanquez about OPAM is that "OCaml's OPAM is a post-GitHub design". This is very true, as much of the workflow for pinning git:// URLs emerged out of being early adopters of GitHub for hosting the MirageOS. OCaml Labs supported two pieces of infrastructure integration around GitHub in 2014:

  • OPAM has a compiler switch feature that lets you run simultaneous OCaml installations and swap between them easily. I used my GitHub API bindings to regularly convert every GitHub pull request into a custom compiler switch. This lets users reporting bugs try out a patched compiler almost immediately upon a fix becoming available.
  • The motivation behind this feature was our collaborator Gabriel Scherer's experiment to enable patch review of OCaml on GitHub, alongside the venerable Mantis bug tracker. We supported this via adding Travis CI support to the main compiler, and also helped to migrate a number of support libraries to GitHub, such as camlp4. These can all be found on the ocaml organisation on GitHub.

Codoc Documentation[edit]

Leo White, David Sheets, Amir Chaudhry and Thomas Gazagnaire led the charge to build a modern documentation generator for OCaml, and published an alpha version of codoc 0.2.0 after a lot of work throughout 2014.

In the 2014 OCaml workshop presentation (abstract, slides, video), we mentioned the "module wall" for documentation and this attempts to fix it. To try it out, simply follow the directions in the README on that repository, or browse some samples of the current, default output of the tool. Please do bear in mind codoc and its constituent libraries are still under heavy development and are *not* feature complete, but we're gathering feedback from early adopters.

codoc's aim is to provide a widely useful set of tools for generating OCaml documentation. In particular, we are striving to:

1. Cover all of OCaml's language features 2. Provide accurate name resolution and linking 3. Support cross-linking between different packages 4. Expose interfaces to the components we've used to build codoc 5. Provide a magic-free command-line interface to the tool itself 6. Reduce external dependencies and default integration with other tools

We haven't yet achieved all of these at all levels of our tool stack but are getting close, and the patches are all under discussion for integration into the mainstream OCaml compiler. codoc 0.2.0 is usable today (if a little rough in some areas like default CSS), and there is a blog post that outlines the architecture of the new system to make it easier to understand the design decisions that went into it.

Community Governance[edit]

As the amount of infrastructure built around the domain grows (e.g. mailing lists, file hosting, bulk building), it is important to establish a governance framework to ensure that it is being used as best needed by the wider OCaml community.

Amir Chaudhry took a good look at how other language communities organise themselves and began putting together a succinct governance framework to capture how the community around `` operates, and how to quickly resolve any conflicts that may arise in the future. He took care to ensure it had a well-defined scope, is simple and self contained, and (crucially) documents the current reality. The result of this work is circulating privately through all the existing volunteers for a first round of feedback, and will go live in the next few months as a living document that explains how our community operates.


One consequence of OCaml's age (close to twenty years old now) is that the tools built around the compiler have evolved fairly independently. While OPAM now handles the high-level package management, there is quite a complex ecosystem of other components that are complex for new users to get to grips with: OASIS, ocamlfind, ocamlbuild, and Merlin to name a few. Each of these components (while individually stable) have their own metadata and namespace formats, further compounding the lack of cohesion of the tools.

Thomas Gazagnaire and Daniel Buenzli embarked on an effort to build an eDSL that unifies OCaml package descriptions, with the short-term aim of generating the support files required by the various support tools, and the long-term goal of being the integration point for the build, test and documentation generation lifecycle of an OCaml/OPAM package. This prototype, dubbed Assemblage has gone through several iterations and design discussions over the summer of 2014. Daniel has since been splitting out portions of it into the Bos OS interaction library.

Assemblage is not released officially yet, but we are committed to resuming work on it this summer when Daniel visits again, with the intention of unifying much of our workflow through this tool. If you are interested in build and packaging systems, now is the time to make your opinion known!

Core Compiler[edit]

We also spent time in 2014 working on the core OCaml language and compiler, with our work primarily led by Jeremy Yallop and Leo White. These efforts were not looking to make any radical changes in the core language; instead, we generally opted for evolutionary changes that either polish rough edges in the language (such as open type and handler cases), or new features that fit into the ML style of building programs.

New Features in 4.02.0[edit]

The OCaml 4.02 series was primarily developed and released in 2014. The ChangeLog generated much user excitement, and we were also pleased to have contributed several language improvements.

Handler Cases and exceptional syntax[edit]

OCaml's try and match constructs are good at dealing with exceptions and values respectively, but neither constructs can handle both values and exceptions. Jeremy Yallop investigated how to handle success more elegantly, and an elegant unified syntax emerged. A simple example is that of a stream iterator that uses exceptions for control flow:

   let rec iter_stream f s =
     match (try Some (MyStream.get s) with End_of_stream -> None) with
     | None -> ()
     | Some (x, s') -> f x; iter_stream f s'

This code is not only verbose, but it also has to allocate an option value to ensure that the iter_stream calls remains tail recursive. The new syntax in OCaml 4.02 allows the above to be rewritten succinctly:

   let rec iter_stream f s =
     match MyStream.get s with
     | (x, s') -> f x; iter_stream f s'
     | exception End_of_stream -> ()

Read more about the background of this feature in Jeremy's blog post, the associated discussion in the upstream Mantis bug, and the final manual page in the OCaml 4.02 release. For an example of its use in a real library, see the Jane Street usage in the s-expression handling library (which they use widely to reify arbitrary OCaml values and exceptions).

Open Extensible Types[edit]

A long-standing trick to build universal containers in OCaml has been to encode them using the exception exn type. There is a similar concept of a universal type in Standard ML, and they were described in the "Open Data Types and Open Functions" paper by Andres Löh and Ralf Hinze in 2006.

Leo White designed, implemented and upstreamed support for extensible variant types in OCaml 4.02. Extensible variant types are variant types that can be extended with new variant constructors.

They can be defined as follows:

   type attr = ..
   type attr += Str of string
   type attr +=
     | Int of int
     | Float of float

Pattern matching on an extensible variant type requires a default case to handle unknown variant constructors, just as is required for pattern matching on exceptions (extensible types use the exception memory representation at runtime).

With this feature added, the OCaml exn type simply becomes a special case of open extensible types. Exception constructors can be declared using the type extension syntax:

       type exn += Exc of int

You can read more about the discussion behind open extensible types in the upstream Mantis bug. If you'd like to see another example of their use, they have been adopted by the latest releases of the Jane Street Core libraries in the Type_equal module.

Modular Implicits[edit]

A common criticism of OCaml is its lack of support for ad-hoc polymorphism. The classic example of this is OCaml's separate addition operators for integers (+) and floating-point numbers (+.). Another example is the need for type-specific printing functions (print_int, print_string, etc.) rather than a single print function which works across multiple types.

Taking inspiration from Scala's implicits and Modular Type Classes by Dreyer et al., Leo White designed a system for ad-hoc polymorphism in OCaml based on using modules as type-directed implicit parameters. The design not only supports implicit modules, but also implicit functors (that is, modules parameterised by other module types) to permit the expression of generic modular implicits in exactly the same way that functors are used to build abstract data structures.

Frederic Bour joined us as a summer intern and dove straight into the implementation, resulting in an online demo and ML Workshop presentation (abstract,video and paper). Another innovation in how we've been trialling this feature is the use of Andy Ray's IOCamlJS to publish an interactive, online notebook that is fully hosted in the browser. You can follow the examples of modular implicits online], or try them out on your own computer via an OPAM switch:

   opam switch 4.02.0+modular-implicits
   eval opam config env
   opam install utop

Some of the early feedback on modular implicits from industrial users was interesting. Jane Street commented that although this would be a big usability leap, it would be dangerous to lose control over exactly what goes into the implicit environment (i.e. the programmer should always know what (a + b) represents by locally reasoning about the code). The current design thus follows the ML discipline of maintaining explicit control over the namespace, with any ambiguities in resolving an implicit module type resulting in a type error.


In addition to ad-hoc polymorphism, support for parallel execution on multicore CPUs is undoubtedly the most common feature request for OCaml. This has been high on our list after improving tooling support, and Stephen Dolan and Leo White made solid progress in 2014 on the core runtime plumbing required.

Stephen initially added thread-local support to the OCaml compiler. This design avoided the need to make the entire OCaml runtime preemptive (and thus a huge patch) by allocating thread-local state per core.

We are now deep into the design and implementation of the programming abstractions built over these low-level primitives. One exciting aspect of our implementation is much of the scheduling logic for multicore OCaml can be written in (single-threaded) OCaml, making the design very flexible with respect to heterogenous hardware and [v ariable IPC performance].

To get feedback on the overall design of multicore OCaml, we presented at OCaml 2014 (slides, video and abstract), and Stephen visited INRIA to consult with the development team and Arthur Chargueraud ( the author of [PASL]). Towards the end of the year, Sivaramakrishnan finished his PhD studies at Purdue and joined our OCaml Labs group. He is the author of MultiMlton, and is now driving the completion of the OCaml multicore work along with Stephen Dolan, Leo White and Mark Shinwell. Stay tuned for updates from us when there is more to show later this year!

Ctypes: a Modular Foreign Function Interface[edit]

The Ctypes library started as an experiment with GADTs by Jeremy Yallop, and has since ballooned in a robust, comprehensive library for safely interacting with the OCaml foreign function interface. The first release came out in time to be included in Real World OCaml in lieu of the low-level FFI (which I was not particularly enamoured with having to explain in a tight page limit).

Throughout 2014, Jeremy expanded support for a number of features requested by users (both industrial and academic) who adopted the library in preference to manually writing C code to interface with the runtime, and issued several updated releases.

C Stub Generation[edit]

The first release of Ctypes required the use of libffi to dynamically load shared libraries and dynamically construct function call stack frames whenever a foreign function is called. While this works for simple libraries, it cannot cover all usecases, since interfacing with C demands an understanding of struct memory layout, C preprocessor macros, and other platform-dependent quirks which are more easily dealt with by invoking a C compiler. Finally, the performance of a libffi-based API will necessarily be slower than writing direct C stub code.

While many other language FFIs provide separate libraries for dynamic and static FFI libraries, we decided to have a go at building a modular version of Ctypes that could handle both cases from a single description of the foreign function interface. The result (dubbed "Cmeleon") remained surprisingly succinct and usable, and now covers almost every use of the OCaml foreign function interface. We submitted a paper to ICFP 2015 dubbed "A modular foreign function interface" that describes it in detail. Here is a highlight of how simple a generic binding looks:

   module Bindings(F : FOREIGN) = struct
     open F
     let gettimeofday = foreign "gettimeofday"
        (ptr timeval @-> ptr timezone @-> returning int)

The FOREIGN module type completely abstracts the details of whether or not dynamic or static binding is used, and handles C complexities such as computing the struct layout on the local machine architecture.

Inverse Stubs[edit]

The other nice result from functorising the foreign function interface emerged when we tried to invert the FFI and serve a C interface from OCaml code (for example, by compiling the OCaml code as a shared library). This would let us begin swapping out C libraries that we don't trust with safer equivalents written in OCaml.

You can see an [example]( of how inverted stubs work via a simple C XML parsing exposed from the Xmlm library. We can define a C struct by:

   (* Define a struct of callbacks (C function pointers) *)
   let handlers : [`handlers] structure typ = structure "handlers"
   let (--) s f = field handlers s (funptr f)
    let on_data      = "on_data"      -- (string @-> returning void)
    let on_start_tag = "on_start_tag" -- (string @-> string @-> returning void)
    let on_end_tag   = "on_end_tag"   -- (void @-> returning void)
    let on_dtd       = "on_dtd"       -- (string @-> returning void)
    let on_error     = "on_error"     -- (int @-> int @-> string @-> returning void)
   let () = seal handlers

and then expose this via C functions:

   module Stubs(I : Cstubs_inverted.INTERNAL) = struct
     (* Expose the type 'struct handlers' to C. *)
     let () = I.structure handlers
     (* We expose just a single function to C.  The first argument is a (pointer
        to a) struct of callbacks, and the second argument is a string
        representing a filename to parse. *)
     let () = I.internal "parse_xml"
        (ptr handlers @-> string @-> returning void) parse

You can find the full source code to these snippets on the ocaml-ctypes-inverted-stubs-example repository on GitHub.

We'll be exploring this aspect of Ctypes further in 2015 for SSL/TLS with David Kaloper and Hannes Mehnert, and Microsoft Research has generously funded a PhD studentship to facilitate the work.

Community Contributions[edit]

Ctypes benefited enormously from several external contributions from the OCaml community. From a portability perspective, A. Hauptmann contributed Windows support, and Thomas Leonard added Xen support to allow Ctypes bindings to work with MirageOS unikernels (which opens up the intriguing possibility of accessing shared libraries across virtual machine boundaries in the future). C language support was fleshed out by Edwin Torok contributing typedef support, Ramkumar Ramachandra adding C99 bools and Peter Zotov integrating native strings.

The winner of "most enthusiastic use of OCaml Labs code" goes to Thomas Braibant of Cryptosense, who used every feature of the Ctypes library (consider multi-threaded, inverted, staged and marshalled bindings) in their effort to hack the hackers. David Sheets comes a close second with his implementation of the FUSE binary protocol, parameterised by version quirks.

If you're using Ctypes, we would love to hear about your particular use. A search on GitHub and OPAM reveals over 20 projects using it already, including industrial use at Cryptosense and Jane Street, and ports to Windows, *BSD, MacOS X and even iPhone and Android. There's a getting started guide, and a mailing list available.

Community and Teaching Efforts[edit]

In addition to the online community building, we also participated in a number of conferences and face-to-face events to promote education about functional programming.

 Conferences and Talks[edit]

There has been a huge growth in the number of quality conferences in recent years, making it tough to choose which ones to attend. ICFP is the academic meeting point that predates most of them, and we participated extensively in 2014 via talks, tutorials and a keynote at the Haskell Symposium. I also served on the program committee and industrial relations chair and took over as the steering committee chair of CUFP. Jeremy Yallop, Thomas Gazagnaire and Leo White all served program committees on workshops, with Jeremy also chairing this year's ML Workshop.

Outside of academic conferences, we participated in a number of non-academic conferences such as QCon, OSCON, CCC, New Directions in OS, FunctionalConf, FPX and FOSDEM. The vast majority of these talks were about the MirageOS, and slides can be found at

The 2048 Browser Game[edit]

Yaron Minsky and I have run OCaml tutorials for ICFP for a few years, and we finally hung up our boots in favour of a new crowd.

Jeremy Yallop and Leo White stepped up to the mark with their ICFP/CUFP 2014 Introduction to OCaml tutorial, which had the additional twist of being taught entirely in a web browser by virtue of using the js_of_ocaml and IOCamlJS. They decided that a good practical target was the popular 2048 game that has wasted many programmer hours here at OCaml Labs. They hacked on it over the summertime, assisted by our visitor Daniel Buenzli who also released useful libraries such as Vg, React, Useri, and Gg.

The end result is satisfyingly playable online, with the source code available at ocamllabs/2048-tutorial.

Thomas Gazagnaire got invited to Bangalore for Functional Conf later in the year, and he extended the interactive tutorial notebook and also ran an OCaml tutorial to a packed room. We were very happy to support the first functional programming conference in India, and hope to see many more such events spring up! Amir Chaudhry then went to Belgium to FOSDEM 2015 where he showed off the 2048 game running as an ARM unikernel to a crowd of attendees at the Xen booth.

Graduate Teaching[edit]

Jeremy Yallop and Leo White (with assistance from Alan Mycroft and myself) also led the design of a new graduate course on Advanced Functional Programming at the Computer Laboratory. This ran in the Lent Term and was over-subscribed by three times the number who pre-registered (due to a number of PhD students and our collaborators from Citrix also attending).

The course materials are freely available online and cover the theory behind functional programming, and then move onto type inference, abstraction and parametricity, GADTs, rows, monads, and staging. We will be running this again in future years, and the lecture materials are already proving useful to answer mailing list questions.

Mentoring Beginners[edit]

We also had the pleasure of mentoring up-and-coming functional programmers via several outreach programs, both face-to-face and remote.

Cambridge Compiler Hacking[edit]

We started the [Cambridge Compiler Hacking]( sessions in a small way towards the end of 2013 in order to provide a local, friendly place to assist people who wanted to dip their toes into the unnecessarily mysterious world of programming language hacking. The plan was simple: provide drinks, pizza, network and a bug list of varying difficulty for attendees to choose from and work on for the evening, with mentoring from the experienced OCaml contributors.

We continued this bi-monthly tradition in 2014, with a regular attendance of 15-30 people, and even cross-pollinated communities with our local F# and Haskell colleagues. We rotated locations from the Cambridge Computer Laboratory to Citrix, Makespace, and the new Cambridge Postdoc Centre. We posted some highlights from sessions towards the start of the year, and are very happy with how it's going. There has even been uptake of the bug list across the water in France, thanks to Gabriel Scherer.

In 2015, we'd like to branch out further and host some sessions in London. If you have a suggestion for a venue or theme, please get in touch!

Summer Programs[edit]

There has been a laudable rise in summer programs designed to encourage diversity in our community, and we of course leap at the opportunity to participate in these when we find them.

Our own students also had the chance to participate in such workshops to get out of Cambridge in the summer! Heidi Howard liveblogged her experiences at the PLMW workshop in Mumbai. Meanwhile, David Sheets got to travel to the slightly less exotic London to liveblog OSIO, and Leonhard Markert covered ICFP 2014 as a student volunteer.

Blogging and Online Activities[edit]

Our blog roll maintains the ongoing stream of activity from the OCaml Labs crew, but there were some particular highlights throughout 2014.

his 0install installation system from Python to OCaml and what you gain with OCaml. This series led to a bunch of interesting feedback on social networking sites, and Thomas joined the group full-time to work on our research into unikernels.

MirageOS, and came up with some crazy experiements, as well as helping to build Vagrant images of the OCaml development environment.

port his website to a Jekyll unikernel.

saw a slew of blogs posts about the surge in MirageOS activity.

It wasn't all just blogging though, and Jeremy Yallop and Leo White in particular participated in some epic OCaml bug threads about new features, and explanations about OCaml semantics on the mailing list.

Amir Chaudhry also continued to curate and develop the content on the website with our external collaborators Ashish Agarwal, Christophe Troestler and Phillippe Wang. Notably, it is now the recommended site for OCaml (with the site being infrequently updated), and also hosts the OCaml Workshop pages. One addition that highlighted the userbase of OCaml in the teaching community came from building a map of all of the universities where the language is taught, and this was Yan Shvartzshnaider's first contribution to the site.

Visitors and Interns[edit]

Finally, a really important part of any community is hanging out with each other to chat over ideas in a friendly environment. As usual, we had a very steady stream of visitors and interns throughout 2014 to facilitate this.

Frederic Bour, Benjamin Farinier and Matthieu Journault joined us as summer interns from their respective universities in France as part of their Masters programs. Frederic worked on modular implicits and gave a great talk at the OCaml Users group. Benjamin and Matthieu worked on Irmin data structures and complexity (and merge-queues and merge-ropes), and Benjamin had his paper on "Mergeable Persistent Data Structures" accepted to JFLA 2015, while Matthieu's work on efficient algorithms for synchronising Irmin DAGs is being integrated into the upstream source code.

Daniel Buenzli repeated his visit from 2013 and spent a productive summer with us, commenting on almost every project we're working on. In his own words (edited for brevity):

"I started by implementing and releasing Uucp, a library to provide efficient access to a selection of the properties of the latest Unicode Character database (UCD). [...] As a side effect of the previous point I took time to write an absolute minimal introduction to Unicode. [...] Since I was in this Unicode business I took the opportunity to propose a 31 loc patch to the standard library for a type to represent Unicode scalar values (an Unicode character to be imprecise) to improve interoperability.

The usual yearly update to OpenGL was announced at the Siggraph conference. This prompted me to update the ctypes-based tgls library for supporting the latest entry point of OpenGL 4.5 and OpenGL ES 3.1. Since the bindings are automatically generated from the OpenGL XML registry the work is not too involved but there's always the odd function signature you don't/can't handle automatically yet.

Spend quite a bit (too much) time on useri, a small multi-platform abstraction for setting up a drawing surface and gather user input (not usury) as React events. Useri started this winter as a layer on top of SDL to implement a CT scan app and it felt like this could be the basis for adding interactivity and animation to Vg/Vz visualizations – js viz libraries simply rely on the support provided by the browser or SVG support but Vg/Vz strives for backend independence and clear separations of concern (up to which limit remains an open question). Unfortunately I couldn't bring it to a release and got a little bit lost in browser compatibility issues and trying to reconcile what browser and SDL give us in terms of functionality and way of operating, so that a maximum of client code can be shared among the supported platforms. But despite this non-release it still managed to be useful in some way, see the next point.

Helped Jeremy and Leo to implement the rendering and interaction for their ICFP tutorial 2048 js_of_ocaml implementation. This featured the use of Gg, Vg, Useri and React and I was quite pleased with the result (despite some performance problems in certain browsers, but hey composable rendering and animation without a single assignement in client code). It's nice to see that all these pains at trying to design good APIs eventually fit together [...]"

A couple of visitors joined us from sunny Morocco, where Hannes Mehnert and David Kaloper had gone to work on a clean-slate TLS stack. They found the MirageOS effort online, and got in touch about visiting. After a very fun summer of hacking, their stack is now the standard TLS option in MirageOS and resulted in the Bitcoin Pinata challenge being issued! Hannes and David have since moved to Cambridge to work on this stack full-time in 2015, but the internships served as a great way for everyone to get to know each other.

We also had the pleasure of visits from several of our usually remote collaborators. Christophe Troestler, Yaron Minsky, Jeremie Diminio and Andy Ray all visited for the annual OCaml Labs review meeting in Christ's College. There were also many academic talks from foreign visitors in our SRG seminar series, ranging from Uday Khedkar from IIT to Oleg Kiselyov deliver multiple talks on staging and optimisation (as well as making a celebrity appearance at the compiler hacking session, and Yaron Minsky delivering an Emacs-driven departmental seminar on his experiences with Incremental computation.

Research Efforts[edit]

The OCaml Labs are of course based in the Cambridge Computer Laboratory, where our day job is to do academic research. Balancing the demands of open source coding, community efforts and top-tier research has be a tricky one, but an effort that has been worthwhile.

Our research efforts are broadly unchanged from 2013 (it takes time to craft good ideas!), and this will not be an exhaustive recap. Instead, we'll summarise them here and point to our [papers ( that describe the work in detail.

  • The MirageOS really found its own feet in 2014, with a summer 2.0 release and an extensive end-of-year recap. The most notable thing has been how well the MirageOS research work has melded with the core OCaml Labs efforts, since much of it has been constructing good quality OCaml libraries to plug holes in the ecosystem. It also served to make us use OPAM on a day-to-day basis for our own work, thus creating an effective feedback loop between open-source and research.
  • In the Trilogy2 and UCN EU projects, we built out MirageOS features such as the Jitsu toolstack for the "just-in-time" summoning of unikernels in response to DNS requests. This paper will be presented next month at USENIX NSDI. It also drove the development of the ARMv7 port, an architecture for which OCaml has an excellent native code generator, as well as more experimental forays into BitCoin incentive schemes for distributed systems.
  • The Irmin Git-like branchable store created by Thomas Gazagnaire matured, with Dave Scott prototyping a complex port of the XenStore database to Irmin, thus letting us show off debugging systems with Git. We had a paper accepted on some early datastructures accepted at JFLA, and Thomas Leonard is building the JavaScript backend for running in-browser, while Yan Schvartzshnaider is experimenting with graph processing over the DAG representation for privacy-friendly queries. KC is investigating how to adapt his PLDI 2015 paper on Quelea into using Irmin as a backend as well.
  • The Higher kinded polymorphism library written by Jeremy Yallop and Leo White was published in FLOPS 2014, forming a basis for building more complex use-cases that need the flexibility of higher kinded types without requiring functorising code.

Some of the most exciting work done in the group as part of the REMS and NaaS projects came towards the end of 2014 and start of 2015, with multiple submissions going into top conferences. Unfortunately, due to most of them being double blind reviewed, we cannot link to the papers yet. Keep an eye on the blog and published paper set, or ask us directly about what's been going on!

Priorities for 2015[edit]

As spring breaks and the weather (almost) becomes bearable again, we're setting our work priorities for the remainder of the year.

  • Tooling Cohesion: The entire core team is focussed on fusing together the individual tools that have been created last year into a cohesive OCaml Platform release that covers the lifecycle of documentation, testing and build. This is being managed by Amir Chaudhry. OPAM remains at the heart of this strategy,

and Louis Gesbert and Thomas Gazagnaire have settled on the OPAM 1.3 roadmap (summary).

  • Multicore: [ KC Sivaramakrishnan] has joined the core OCaml Labs fulltime to drive the multicore work into a publically testable form. Leo White recently departed after many productive years in Cambridge to head into a career in industry (but still remains very much involved with OCaml development!).
  • Language Evolution: Jeremy Yallop continues to drive our efforts on staged programming, modular implicits, and a macro system for OCaml, all of which are key features that make building complex, reliable systems more tractable than ever.

I'd like to thank the entire team and wider community for a wonderfully enjoyable 2014 and start of 2015, and am very thankful to the funding and support from Jane Street, Citrix, British Telecom, RCUK, EPSRC, DARPA and the EU FP7 that made it all possible. As always, please feel free to contact any of us directly with questions, or reach out to me personally with any queries, concerns or bars of chocolate as encouragement.


This time last year in 2012, I had just announced the formation of a new group called OCaml Labs in the Cambridge Computer Lab that would combine research and community work towards the practical application of functional programming. An incredible year has absolutely flown by, and I've put together this post to summarise what's gone on, and point to our future directions for 2014.

The theme of our group was not to be pure research, but rather a hybrid group that would take on some of the load of day-to-day OCaml maintenance from INRIA, as well as help grow the wider OCaml community. To this end, all of our projects have been highly collaborative, often involving colleagues from OCamlPro, INRIA, Jane Street, Lexifi and Citrix.

This post covers progress in tooling, the compiler and language, community efforts, research projects and concludes with our priorities for 2014.


At the start of 2013, OCaml was in the interesting position of being a mature decades-old language with a small, loyal community of industrial users who built mission critical applications using it. We had the opportunity to sit down with many of them at the OCaml Consortium meeting and prioritise where we started work. The answer came back clearly: while the compiler itself is legendary for its stability, the tooling around it(such as package management) was a pressing problem.


Our solution to this tooling was centered around the OPAM package manager that OCamlPro released into beta just at the end of 2012, and had its first stable release in March 2013. OPAM differs from most system package managers by emphasising a flexible distributed workflow that uses version constraints to ensure incompatible libraries aren't mixed up (important for the statically-typed OCaml that is very careful about dependencies). Working closely with OCamlPro we developed a git-based workflow to make it possible for users (both individual or industrial) to easily build up their own package repositories and redistribute OCaml code, and started curating the package repository.

The results have been satisfying: we started with an initial set of around 100 packages in OPAM (mostly imported by the 4 developers), and ended 2013 with 587 unique packages and 2000 individual versions, with contributions from 160 individuals. We now have a curated central package repository for anyone to submit their OCaml code, several third-party remotes are maintained (e.g. the Xen Project and Ocsigen). We also regularly receive releases of the Core libraries from Jane Street, and updates from sources as varied as Facebook, Coherent PDF, to the Frenetic SDN research.

A notable contribution from OCamlPro during this time was to clarify the licensing on the package repository to be the liberal CC0, and also to pass ownership to the OCaml organization on GitHub, where it's now jointly maintained by OCaml Labs, OCamlPro and anyone else that wishes to contribute.

A lens into global OCaml code[edit]

It's been quite interesting just watching all the varied code fly into the repository, but stability quickly became a concern as the new packages piled up. OCaml compiles to native code on not just x86, but also PowerPC, Sparc and ARM CPUs. We kicked off various efforts into automated testing: firstly David Sheets built the OCamlot daemon that would schedule builds across all the exotic hardware. Later in the year, the Travis service launched support for testing from GitHub pull requests, and this became the front line of automated checking for all incoming new packages to OPAM.

A major headache with automated testing is usually setting up the right build environment with external library dependencies, and so we added Docker support to make it easier to bulk-build packages for local developer use, with the results of builds available publically for anyone to help triage. Unfortunately fixing the bugs themselves is still a very manual process, so more volunteers are always welcome to help out!

We're going to be really seeing the rewards from all this effort as OCaml 4.02 development proceeds, since we can now adopt a data-driven approach to changing language features instead of guessing how much third-party code will break. If your code is in OPAM, then it'll be tested as new features such as module aliases, injectivity and extension points show up.

Better documentation[edit]

The venerable OCamlDoc tool has done an admirable job for the last decade, but is increasingly showing its age due to a lack of support for cross-referencing across packages. We started working on this problem in the summer when Vincent Botbol visited us on an internship, expecting it to be a quick job to come up with something as good as Haskell's excellent Haddock online documentation.

Instead, we ran into the "module wall": since OCaml makes it so easy to parameterise code over other modules, it makes it hard to generate static documentation without outputting hundreds of megabytes of HTML every time. After some hard work from Vincent and Leo, we've got a working prototype that lets you simply run `opam install opam-doc && opam doc core async` to generate package documentation. You can see the results for Mirage online, but expect to see this integrated into the main OCaml site for all OPAM packages as we work through polishing up the user interface.

Turning OPAM into libraries[edit]

The other behind-the-scenes effort for OPAM has been to keep the core command-line tool simple and stable, and to have it install OCaml libraries that can be interfaced with by other tools to do domain-specific tasks. Thomas Gazagnaire, Louis Gesbert and David Sheets have been steadily hacking away at this and we now have opamfu to run operations over all packages, and an easy-to-template opam2web that generates the live website.

This makes OPAM easier to deploy within other organizations that want to integrate it into their workflow. For example, the software section of the OCaml Labs website is regularly generated from a search of all OPAM packages tagged `ocamllabs`. We also used it to rewrite the entire OPAM repository in one epic diff to add external library dependencies via a [command-line shim](


All of this effort is geared towards making it easier to maintain reusable local OPAM installations. After several requests from big universities to help out their teaching needs, we're putting together all the support needed to easily redistribute OPAM packages via an "OPAM-in-a-Box" command that uses Docker containers to let you clone and do lightweight modifications of OCaml installations.

This will also be useful for anyone who'd like to run tutorials or teach OCaml, without having to rely on flaky network connectivity at conference venues: a problem we've suffered from too!

Core Compiler[edit]

Starting to work on a real compiler can often be a daunting prospect, and so one initiative we started this year is to host regular compiler hacking sessions where people could find a curated list of features to work on, with the regular developers at hand to help out when people get stuck, and free beer and pizza to oil the coding wheels. This has worked out well, with around 20 people showing up on average for the three we held, and several patches submitted upstream to OCaml. Gabriel Scherer and Damien Doligez have been helping this effort by tagging project_id=1&sticky_issues=1&sortby=last_updated&dir=DESC&highlight_changed=24&hide_status_id=90&tag_string=junior_job junior jobs in the OCaml Mantis bug tracker as they are filed.

Syntax transformations and extension points[edit]

Leo White started the year fresh out of completing his PhD with Alan Mycroft, and before he realized what he'd gotten himelf into was working with Alain Frisch on the future of syntax transformations in OCaml. We started off our first wg-camlp4 working group on the new host, and a spirited discussion started that went February/thread.html on and on for several months. It ended with a very satisfying design for a simpler extension points mechanism which Leo presented at the OCaml 2013 workshop at ICFP, and is now merged into OCaml 4.02-trunk.


Not all of the working groups were quite as successful in coming to a conclusion as the Camlp4 one. On the Platform mailing list, Gabriel Scherer started a discussion on the design for namespaces in OCaml. The resulting discussion was useful in separating multiple concerns that were intermingled in the initial proposal, and Leo wrote a comprehensive blog post on a proposed namespace design.

After further discussion at ICFP 2013 with Jacques Garrigue later in the year, it turns out adding support for module aliases would solve much of the cost associated with compiling large libraries such as Core, with no backwards compatibility issues. This solution has now been integrated into OCaml 4.02.0dev and is being tested with Core.

Delving into the bug tracker[edit]

Jeremy Yallop joined us in April, and he and Leo also leapt into the core compiler and started triaging issues on the OCaml bug tracker. This seems unglamorous in the beginning, but there rapidly turned out to be many fascinating threads that shed light on OCaml's design and implementation through seemingly harmless bugs. Here is a pick of some interesting threads through the year that we've been involved with:

This is just a sample of some of the issues solved in Mantis; if you want to learn more about OCaml, it's well worth browsing through it to learn from over a decade of interesting discussions from all the developers.

Thread-local storage runtime[edit]

While OCamlPro was working on their reentrant OCaml runtime, we took a different tack by adding thread-local storage to the runtime instead, courtesy of Stephen Dolan. This is an important choice to make at the outset of adding multicore, so both approaches are warranted. The preemptive runtime adds a lot of code churn (due to adding a context parameter to most function calls) and takes up a register, whereas the thread-local storage approach we tried doesn't permit callbacks to different threads.

Much of this work isn't interesting on its own, but forms the basis for a fully multicore runtime (with associated programming model) in 2014. Stay tuned!


One other complaint from the Consortium members was quite surprising: the difficulty of using the OCaml foreign function interface safely to interface with C code. Jeremy Yallop began working on the ctypes library that had the goal of eliminating the need to write any C code at all for the vast majority of foreign bindings.

Instead, Ctypes lets you describe any C function call as an OCaml value, and provides various linkage options to invoke that function into C. The first option he implemented was a `dlopen` interface, which immediately brought us the same level of functionality as the Python or Haskell Ctypes equivalents. This early code was in itself startlingly useful and more pleasant to use than the raw FFI, and various folk (such as David Sheets' libsodium cryptography bindings) started adopting it.

At this point, I happened to be struggling to write the Foreign Function Interface chapter of Real World OCaml without blowing through our page budget with a comprehensive explanation of the existing system. I decided to take a risk and write about Ctypes instead, since it let new users to the language have a *far* more productive experience to get started. Xavier Leroy pointed out some shortcomings of the library in his technical book review, most notably with the lack of an interface with C. The design of Ctypes fully supports alternate linking mechanisms than just `dlopen` though, and Jeremy has added automatic C stub generation support as well. This means that if you use Ctypes to build an OCaml binding in 2014, you can choose several mechanisms for the same source code to link to the external system. Jeremy even demonstrated a forking model at OCaml 2013 that protects the OCaml runtime from the C binding via process separation.

The effort is paying off: Daniel Bünzli ported SDL2 using ctypes, and gave us extensive feedback about any missing corner cases, and the resulting bindings don't require any C code to be written. Jonathan Protzenko even used it to implement an OCaml controller for the [ttp:// Adafruit Raspberry Pi RGB LCD]!

Community Efforts[edit]

Our community efforts were largely online, but we also hosted visitors over the year and regular face-to-face tutorials.

Online at[edit]

While the rest of the crew were hacking on OPAM and OCaml, Amir Chaudhry and Philippe Wang teamed up with Ashish Agarwal and Christophe Troestler to redesign and relaunch the OCaml website. Historically, OCaml's homepage has been the domain, and the effort was begun by Christophe and Ashish some years ago to modernize the web presence.

The webpages were already rather large with complex scripting (for example, the 99 Problems page runs the OCaml code to autogenerate the output). Philippe developed a template DSL that made it easier to unify a lot of the templates around the website, and also a Markdown parser that we could link to as a library from the rest of the infrastructure without shelling out to Pandoc.

Meanwhile, Amir designed a series of interactive wireframe sketches and gathered feedback on it from the community. A local design agency in Cambridge helped with visual look and feel, and finally at the end of the summer we began the migration to the new website, followed by a triumphant switchover in November to the design you see today.

The domain isn't just limited to the website itself. Leo and I set up a SVN-to-Git mirror of the OCaml compiler Subversion repository on the GitHub OCaml organization, which is proving popular with developers. There is an ongoing effort to simplify the core compiler tree by splitting out some of the larger components, and so camlp4 is also now hosted on that organization, along with OASIS. We also administer several subdomains of, such as the mailing lists and the OPAM repository, and other services such as the OCaml Forge are currently migrating over. This was made significantly easier thanks to sponsorship from Rackspace Cloud (users of XenServer which is written in OCaml). They saw our struggles with managing physical machines and gave us developer accounts, and all of the infrastructure is now hosted on Rackspace. We're very grateful to their ongoing help!

If you'd like to contribute to infrastructure help (for example, I'm experimenting with a GitLab mirror), then please join the mailing list and share your thoughts. The website team also need help with adding content and international translations, so head over to the website issue tracker and start proposing improvements you'd like to see.

Next steps for[edit]

The floodgates requesting features opened up after the launch of the new look and feel. Pretty much everyone wanted deeper OPAM integration into the main website, for features such as:

  • Starring and reviewing packages
  • Integrating the opam-doc documentation with the metadata
  • Display test results and a compatibility matrix for non-x86 and non-Linux architectures.
  • Link to blog posts and tutorials about the package.

Many of these features were part of the original wireframes but we're being careful to take a long-term view of how they should be created and maintained. Rather than building all of this as a huge bloated opam2web extension, David Sheets (our resident relucant-to-admit-it web expert) has designed an overlay directory scheme that permits the overlaying of different metadata onto the website. This lets one particular feature (such as blog post aggregation) be handled separately from the others via Atom aggregators.

Real World OCaml[edit]

A big effort that took up most of the year for me was finishing and publishing an O'Reilly book called Real World OCaml with Yaron Minsky and Jason Hickey. Yaron describes how it all started in his blog post, but I learnt a lot from developing a book using the open commenting scheme that we developed just for this.

In particular, the book ended up shining a bright light into dark language corners that we might otherwise not have explored in OCaml Labs. Two chapters of the book that I wasn't satisfied with were the objects and classes chapters, largely since neither Yaron nor Jason nor I had ever really used their full power in our own code. Luckily, Leo White decided to pick up the baton and champion these oft-maligned (but very powerful) features of OCaml, and the result is the clearest explanation of them that I've read yet. Meanwhile, Jeremy Yallop helped out with extensive review of the Foreign Function Interface chapter that used his ctypes library. Finally, Jeremie Dimino at Jane Street worked hard on adding several features to his utop toplevel that made it compelling enough to become our default recommendation for newcomers.

All in all, we ended up closing over 2000 comments in the process of writing the book, and I'm very proud of the result ( freely available [online](), but do programming/dp/144932391X/ buy a copy if you can to support it). Still, there's more I'd like to do in 2014 to improve the ease of using OCaml further. In particular, I removed a chapter on packaging and build systems since I wasn't happy with its quality, and both Thomas Gazagnaire and I intend to spend time in 2014 on improving this part of the ecosystem.

Tutorials and Talks[edit]

We had a lively presence at ICFP 2013 this year, with the third iteration of the OCaml 2013 held there, and Stephen Dolan presenting a paper in the main conference. I liveblogged the workshop as it happened, and all the talks we gave are linked from the program. The most exciting part of the conference for a lot of us were the two talks by Facebook on their use of OCaml: first for program analysis using Pfff and then to migrate their massive PHP codebase using an OCaml compiler. I also had the opportunity to participate in a panel at the Haskell Workshop on whether Haskell is too big to fail yet; lots of interesting perspectives on scaling another formerly academic language into the real world.

Yaron Minsky and I have been giving tutorials on OCaml at ICFP for several years, but the release of Real World OCaml has made it significantly easier to give tutorials without the sort of labor intensity that it took in previous years (one memorable ICFP 2011 tutorial that we did took almost 2 hours to get everyone installed with OCaml. In ICFP 2013, it took us 15 minutes or so to get everyone started). Still, giving tutorials at ICFP is very much preaching to the choir, and so we've started speaking at more general-purpose events.

Our first local effort was FPDays in Cambridge, where Jeremy Yallop and Amir Chaudhry ran the tutorial with help from Phillipe Wang, Leo White and David Sheets. The OCaml session there ended up being the biggest one in the entire two days, and Amir wrote up their experiences. One interesting change from our ICFP tutorial is that Jeremy used js_of_ocaml to teach OCaml via JavaScript by building a fun Monty Hall game.

Visitors and Interns[edit]

Since OCaml Labs is a normal group within the Cambridge Computer Lab, we often host academic visitors and interns who pass through. This year was certainly diverse, and we welcomed a range of colleagues:

We were also visited several times by Wojciech Meyer from ARM, who was an OCaml developer who maintained (among other things) the ocamlbuild system and worked on DragonKit (an extensible LLVM-like compiler written in OCaml). Wojciech very sadly passed away on November 18th, and we all fondly remember his enthusiastic and intelligent contributions to our small Cambridge community.

We also hosted visitors to live in Cambridge and work with us over the summer. In addition to Vincent Botbol (who worked on OPAM-doc as described earlier) we had the pleasure of having Daniel Bünzli and Xavier Clerc work here. Here's what they did in their own words.

Xavier Clerc: OCamlJava

Xavier Clerc took a break from his regular duties at INRIA to join us over the summer to work on OCaml-Java and adapt it to the latest JVM features. This is an incredibly important project to bridge OCaml with the huge Java community, and here's his report:

"After a four-month visit to the OCaml Labs dedicated to the OCaml-Java project, the time has come for an appraisal! The undertaken work can be split into two areas: improvements to code generation, and interaction between the OCaml & Java languages. Regarding code generation, several classical optimizations have been added to the compiler, for example loop unrolling, more aggressive unboxing, better handling of globals, or partial evaluation (at the bytecode level). A new tool, namely ocamljar, has been introduced allowing post-compilation optimizations. The underlying idea is that some optimizations cannot always be applied (e.g. depending whether multiple threads/programs will coexist), but enabling them through command-line flags would lead to recompilation and/or multiple installations of each library according to the set of chosen optimizations. It is thus far more easier to first build an executable jar file, and then modify it according to these optimizations. Furthermore, this workflow allows the ocamljar tool to take advantage of whole-program information for some optimizations. All these improvements, combined, often lead to a gain of roughly 1/3 in terms of execution time.

Regarding language interoperability, there are actually two directions depending on whether you want to call OCaml code from Java, or want to call Java code from OCaml. For the first direction, a tool allows to generate Java source files from OCaml compiled interfaces, mapping the various constructs of the OCaml language to Java classes. It is then possible to call functions, and to manipulate instances of OCaml types in pure Java, still benefitting from the type safety provided by the OCaml language. In the other direction, an extension of the OCaml typer is provided allowing to create and manipulate Java instances directly from OCaml sources. This type extension is indeed a thin layer upon the original OCaml typer, that is mainly responsible for encoding Java types into OCaml types. This encoding uses a number of advanced elements such as polymorphic variants, subtyping, variance annotations, phantom typing, and printf-hack, but the end-user does not have to be aware of this encoding. On the surface, the type of instances of the Java Object classes is `java'lang'Object java_instance`, and instances can be created by calling Java.make Object().

While still under heavy development, a working prototype is available, and bugs can be reported. Finally, I would like to thank the OCaml Labs for providing a great working environment.

Daniel Bünzli: Typography and Visualisation

Daniel joined us from Switzerland, and spent some time at Citrix before joining us in OCaml Labs. All of his software is now on OPAM, and is seeing ever-increasing adoption from the community.

"Released a first version of Vg I'm especially happy about that as I wanted to use and work on these ideas since at least 2008. The project is a long term project and is certainly not finished yet but this is already a huge step.

Adjusted and released a first version of Gg. While the module was already mostly written before my arrival to Cambridge, the development of Vg and Vz prompted me to make some changes to the module.

Released Otfm, a module to decode OpenType fonts. This is a work in progress as not every OpenType table has built-in support for decoding yet. But since it is needed by Vg's PDF renderer I had to cut a release. It can however already be used to implement certain simple things like font kerning with Vg, this can be seen in action in the `vecho` binary installed by Vg.

Started to work on Vz, a module for helping to map data to Vg images. This is really unfinished and is still considered to be at a design stage. There are a few things that are however well implemented like (human) perceptually meaningful color palettes and the small folding stat module (`Vz.Stat`). However it quickly became evident that I needed to have more in the box w.r.t. text rendering in Vg/Otfm. Things like d3js entirely rely on the SVG/CSS support for text which makes it easy to e.g. align things (like tick labels on such drawings). If you can't rely on that you need ways of measuring rendered text. So I decided to suspend the work on Vz and put more energy in making a first good release of Vg. Vz still needs quite some design work, especially since it tries to be independent of Vg's backend and from the mechanism for user input.

Spent some time figuring out a new "opam-friendly" release workflow in pkgopkg. One of my problem is that by designing in the small for programming in the large --- what a slogan --- the number of packages I'm publishing is growing (12 and still counting). This means that I need to scale horizontally maintenance-wise unhelped by the sad state of build systems for OCaml. I need tools that make the release process flawless, painless and up to my quality standards. This lead me to enhance and consolidate my old scattered distribution scripts in that repo, killing my dependencies on Oasis and ocamlfind along the way. '(edited for brevity, see here)

Daniel also left his bicycle here for future visitors to use, and the "Bünzli-bike" is available for our next visitor! (Louis Gesbert even donated lights, giving it a semblance of safety).

Industrial Fellows[edit]

Most of our regular funding bodies such as EPSRC or EU FP7 provide funding, but leave all the intellectual input to the academics. A compelling aspect of OCaml Labs has been how involved our industrial colleagues have been with the day-to-day problems that we solve. Both Jane Street and Citrix have senior staff regularly visiting our group and working alongside us as industrial fellows in the Computer Lab.

  • Mark Shinwell from Jane Street Europe has been working on improving the state of native debugging in OCaml, by adding extended DWARF debugging information to the compiler output. Mark is also a useful source of feedback about the forthcoming design of multicore, since he has daily insight into a huge production codebase at Jane Street (and can tell us about it without us requiring access!).
  • Dave Scott is the principal architect of XenServer at Citrix in Cambridge. This year has been transformative for that project, since Citrix open-sourced XenServer to GitHub and fully adopted OPAM into their workflow. Dave is the author of numerous libraries that have all been released to OPAM, and his colleagues Jon Ludlam and Euan Harris are also regular visitors who have also been contributors to the OPAM and Mirage ecosystems.

Research Projects[edit]

The other 100% of our time at the Labs is spent on research projects. When we started the group, I wanted to set up a feedback loop between local people using OCaml to build systems, with the folk *developing* OCaml itself. This has worked out particularly well with a couple of big research projects in the Lab.


Mirage is a library operating system written in OCaml that compiles source code into specialised Xen microkernels, developed at the Cambridge Computer Lab, Citrix and the Horizon Digital Economy institute at Nottingham. This year saw several years of effort culminate in the first release of Mirage 1.0 as a self-hosting entity. While Mirage started off as a quick experiment into building specialised virtual appliances, it rapidly became useful to make into a real system for use in bigger research projects. You can learn more about Mirage here, or read the Communications of the ACM article that Dave Scott and I wrote to close out the year.

This project is where the OCaml Labs "feedback loop" has been strongest. A typical Mirage application consists of around 50 libraries that are all installed via OPAM. These range from device drivers to protocol libraries for HTTP or DNS, to filesystems such as FAT32. Coordinating regular releases of all of these would be near impossible without using OPAM, and has also forced us to use our own tools daily, helping to sort out bugs more quickly. You can see the full list of libraries on the OCaml Labs software page.

Mirage is also starting to share code with big projects such as XenServer now, and we have been working with Citrix engineers to help them to move to the Core library that Jane Street has released (and that is covered in Real World OCaml). Moving production codebases this large can take years, but OCaml Labs is turning out to be a good place to start unifying some of the bigger users of OCaml into one place. We're also now an official Xen Project incubator project, which helps us to validate functional programming to other Linux Foundation efforts.

Nymote and User Centric Networking[edit]

The release of Mirage 1.0 has put us on the road to simplifying embedded systems programming. The move to the centralized cloud has led to regular well-publicised privacy and security threats to the way we handle our digital infrastructure, and so Jon Crowcroft, Richard Mortier and I are leading an effort to build an alternative privacy-preserving infrastructure using embedded devices as part of the User Centric Networking project, in collaboration with a host of companies led by Technicolor Paris. This work also plays on the strong points of OCaml: it already has a fast ARM backend, and Mirage can easily be ported to the new Xen/ARM target as hardware becomes available.

One of the most difficult aspects of programming on the "wide area" Internet are dealing with the lack of a distributed identity service that's fully secure. We published our thoughts on this at the USENIX Free and Open Communications on the Internet workshop, and David Sheets is working towards a full implementation using Mirage. If you're interested in following this effort, Amir Chaudhry is blogging at the Nymote project website, where we'll talk about the components as they are released.

 Data Center Networking[edit]

At the other extreme from embedded programming is datacenter networking, and we started the Network-as-a-Service research project with Imperial College and Nottingham. With the rapid rise of Software Defined Networking this year, we are investigating how application-specific customisation of network resources can build fast, better, cheaper infrasructure. OCaml is in a good position here: several other groups have built OpenFlow controllers in OCaml (most notably, the Frenetic Project), and Mirage is specifically designed to assemble such bespoke infrastructure.

Another aspect we've been considering is how to solve the problem of optimal connectivity across nodes. TCP is increasingly considered harmful in high through, high-density clusters, and George Parisis led the design of Trevi, which is a fountain-coding based alternative for storage networking. Meanwhile, Thomas Gazagnaire (who joined OCaml Labs in November), has been working on a branch-consistent data store called Irminsule which supports scalable data sharing and reconciliation using Mirage. Both of these systems will see implementations based on the research done this year.

 Higher Kinded Programming[edit]

Jeremy Yallop and Leo White have been developing an approach that makes it possible to write programs with higher-kinded polymorphism (such as monadic functions that are polymorphic in the monad they use) without using functors. It's early days yet, but there's a library available on OPAM that implements the approach, and a draft paper that outlines the design.

Priorities for 2014[edit]

This year has been a wild ride to get us up to speed, but we now have a solid sense of what to work on for 2014. We've decided on a high-level set of priorities led by the senior members of the group:

  • Multicore: Leo White will be leading efforts in putting an end-to-end multicore capable OCaml together.
  • Metaprogramming: Jeremy Yallop will direct the metaprogramming efforts, continuing with Ctypes and into macros and extension points.
  • Platform: Thomas Gazagnaire will continue to drive OPAM development towards becoming the first OCaml Platform.
  • Online: Amir Chaudhry will develop the online and community efforts that started in 2013.

These are guidelines to choosing where to spend our time, but not excluding other work or day-to-day bugfixing. Our focus on collaboration with Jane Street, Citrix, Lexifi, OCamlPro and our existing colleagues will continue, as well as warmly welcoming new community members that wish to work with us on any of the projects, either via internships, studentships or good old-fashioned open source hacking.

I appreciate the whole team's feedback in editing this long post into shape, the amazing professorial support from Jon Crowcroft, Ian Leslie and Alan Mycroft throughout the year, and of course the funding and support from Jane Street, Citrix, RCUK, EPSRC, DARPA and the EU FP7 that made all this possible. Roll on 2014, and please do get in touch with me with any queries!


The rain continues to plummet down relentlessly as "summer" starts in OCaml Labs. The most exciting news has been the public release of the Real World OCaml, which hit the front page of the usual news aggregators and generated huge interest! This (reminiscent of the Xen 1.0 release) promptly took down servers for a couple of hours, but we managed to minimise downtime in time for the Californians waking up.

O'Reilly has also started selling PDF copies of the book under their Rough Cuts program. This gives you a copy of the final book when it's released too. Commenting is still open on the online version, so please do feel free to participate there if you have time.

Systems Projects[edit]

Mirage Anil and Dave did the last of the sweeping build changes to make Mirage friendlier to use for beginners. Previously, we required a custom OPAM switch to build kernels, but now we use packages to separate the choice of compiler and packages. This of course breaks all our documentation, but we're going to do a big sweep in July before OSCON with the new scheme. Vincent has also been burning through the core platform libraries, cleaning them up and adding documentation strings. He is also building a shared memory vchan driver that will make parallel-Mirage unikernels very easy to coordinate on the same host.

The huge news from our friends at Citrix is the open-sourcing of XenServer, which is the popular Citrix product that embeds the OCaml XAPI cloud management stack. There are almost 100 major components released as part of this, several of which can be directly reused with Mirage. Mirage was always an ambitious project, but it's all coming together now thanks to bold moves such as this from Citrix!

Signpost We woke up to the excellent but slightly scary news that our USENIX FOCI paper was accepted. This now means that we get to present it in August at USENIX Security, but the team is now racing to pull together the prototypes into a complete system before the conference. Nothing like a deadline to focus the mind! We're also working on the camera-ready version of the paper, which we will share here when it's ready.

Platform Projects[edit]

OCamlot David Sheets did an astounding job at pulling together a working continuous build system in a very short amount of time, and promptly managed to melt some of the older [../tasks/platform.html#Machine%20Pool non-x86 machines] in Anil's office. Once Anil sadly replaced them, the builder churned through a matrix of different compiler versions (4.0,4.1dev,4.2dev), architectures (x86, x86_64, ARM, PowerPC), and operating systems (Debian, Ubuntu, FreeBSD, OpenBSD to start with). There's a URL, but the next step is to retire this and move it to a proper home at

Having continuous build for OPAM is really, really useful though, as it lets us vet pull requests on several architectures before merging them. It also let Anil repair OCaml on OpenBSD/macppc too, which is possibly the most obscure fix he's done in a while.

The next steps with OCamlot are to take a shot at porting the core to Jenga, which is Jane Street's next-generation distributed build system. This should let us improve the fault-tolerance and logging aspects of it before putting it properly into production later in the summer.

Ctypes The May release brought with it a good chunk of feedback, so Jeremy spent time incorporating that and contributing to the Real World OCaml ctypes chapter. He also added support for garbage-collecting closures passed to C, and also very cool support for printing C types and values. Our friends at Citrix have started looking at ctypes, and Rob Hoes has already used it to write bindings to the Netlink Protocol Library Suite.

OPAM-doc Vincent Botbol got the documentation generator stable enough to pass the Core library through. This is particularly challenging since Core exercises pretty much every trick in the book when it comes to the use of the module system. However, Vincent successfully demonstrated the workflow of OPAM-doc at the end-of-month meeting, and is aiming to have a public release via OPAM in July (hopefully in time for the next beta release of Real World OCaml, which uses Core heavily).

Visualisation libraries Daniel Bünzli has been spending a few months based in Citrix, working on a foundational new declarative drawing library written in pure OCaml. The Vg is already quite functional despite still being in beta, and features a Javascript backend that renders to both SVG and Canvas in HTML5. That's not all though! He's also developing the Vz visualization library that uses Vg to assemble more complex scenes and graphs. Daniel's going to join us in OCaml Labs for the remainder of the summer, so we're looking forward to developing this more and using it on our various Platform projects such as OCamlot.


Real World OCaml As mentioned earlier, the beta release of RWO went splendidly, with a pleasing vibe that the book is what people expected. There were some interesting criticisms of the choice of Github authentication, but we've had over 6000 registered commentators despite this (and of course, we have plans brewing to tackle the identity problem).

No beta release is perfect, of course, and our now-public commenting system has resulted in over 1500 issues being raised. Well, that's all of Yaron, Anil and Jason's free time gone for some time! We're in the process of looking at the site as a whole and designing the workflow we'd like to have for growing and maintaining it. Some discussions have taken place about using Markdown in place of the current HTML snippets, which would make it easier for external contributors to get involved. In the meantime, Amir has converted the current site to Markdown format to see how this process would work in practice. You can see his experimenting and scripts in the temporary repo in the `markdown-site/` folder. Philippe also showed off MPP at the internal meetings, and is stabilising it for a public release this summer (once it has been integrated into the workflow).

This month also had a number of programming language gurus show up at the Lab for the Algebraic Effects and Handlers workshop organised by Sam Staton. Most of the group attended this, as we're all interested in how to encode effects for several of our projects (most notably [../tasks/t2.html#Irminsule Irminsule]).

We also enjoyed a visit by Benoît Vaugon, who gave a talk on his OCamlCC OCaml-to-C compiler, and also participated in a talk on OCAPIC]. He also chatted with us about his alternative GADT-based implementation ofPrintf, which promises to both speed up and simplify the printer support in OCaml (and also relieve Mirage of another dependency on `libc`).



May is exam time in Cambridge, and the corridors of the OCaml Labs resounded with the wailing of frantic students finishing their dissertations and preparing for exams. We welcomed Vincent Botbol to join us for a summer internship, and he started hacking on the new [../tasks/platform.html#OPAM%20Doc opam-doc] right away.

Anil, Thomas, Leo and Amir also visited Jane Street HQ in New York City, where we had a productive couple of days reviewing our projects and getting feedback from them about approaches to multicore and type system enhancements. [ Ashish Agarwal] also organised a fun evening with the New York OCaml Users Group, where Anil and Thomas presented our plans for the nascent OCaml Platform.

Systems Projects[edit]

Mirage This was a month of consolidation and bugfixing in Mirage. We've been settling into weekly meetings to coordinate the hacking between us and Citrix, and the minutes (1 2 3) may be useful if you want to catch up. The biggest bugbear is always the build system, and we've been exploring the use of Jenga as the eventual async-aware coordination and build system for running Mirage kernels. Dave made great progress with a message-switch that coordinates multiple kernels, and Balraj fixed several performance regressions in the TCP/IP stack by building unit tests that spawn millions of parallel TCP connections.

Signpost We took a break from building prototypes to submit a paper on the basic design to the USENIX Free and Open Communications (FOCI 2013) workshop. Haris and Heidi blazed a path on writing this paper, and we've got even more ideas rolling around about how to use DNSSEC to break the cloud deadlock. The ocaml-dns continues to grow features too.

Platform Projects[edit]

Ctypes Jeremy announced the first release of a new foreign-function mechanism for OCaml that doesn't require you to write any C stubs at all! You can browse the source code and tutorial), and install it via OPAM. This is very much the first 0.1 release, and we have exciting future developments to turn this into a full-fledged replacement for the fast-but-rather-difficult-to-use-right OCaml FFI.

OPAM-doc Vincent Botbol started building on Leo's work on the new opam-doc tool. This is intended to replace the venerable `ocamldoc` with one that uses all the latest features of the compiler. In particular, it can use the new typed AST `cmt` output to avoid duplicating the compiler functionality, and can also build up a global package table to generate complete cross-references across an entire OPAM collection.

OCamlot David has been building up the libraries and tools needed for the [../tasks/platform.html#OCamlot%200.2.0 continuous build] infrastructure. This includes much-improved [ocaml-github](, bindings, which are now being used to power the Real World OCaml site as well as well as OCamlot. In addition, he's got an interesting collection of regular expressions to automatically triage common failures from OPAM (such as missing external dependencies), that should help reduce the manual burden of getting thousands of tests results dumped on the small OPAM team.

Compiler Projects[edit]

OCaml-Java Xavier Clerc has been hacking away at his next-generation OCaml-Java backend (using many new features in JDK7). He's released a [preview]( of the bindings to Java concurrency, and is looking for feedback on it.

Performance Profiling Mark Shinwell has been hacking on improving the integration of the runtime with `perf`. This should give us the hooks to reliably track where memory was allocated. His branch isn't going to land in OCaml 4.1, but should be available as an OPAM switch for people to easily try out when it's more stable.

Outreach[edit] Philippe and Amir have been putting their heads together with Christophe and Ashish to turn the build pipeline into something a little more structured. Philippe is building a template processor for this purpose. The OCaml site is a more complicated than the average site due to our desire to embed js_of_ocaml interactive toplevels throughout the tutorials, and also to have active OPAM integration throughout the site to make it easier for newcomers to sample the language.

The design of a handful of pages are also now available to preview, if you don't mind some manual git cloning. The best way to do this is to clone the temporary repo onto your local machine and look in the `new-design/_site` directory. There are examples of the home page, 100 lines of OCaml page and several others. Since we're just getting started with applying these changes the site isn't clicky (yet). For some extra fun, try resizing your browser window and see how the pages reflow to suit smaller (mobile) screens!

Real World OCaml Anil, Yaron and Jason continue to work hard on getting a release out of the door. We shipped a final alpha6 this month that is chapter-complete, and have been preparing for a big public June release of the book. Thousands of comments have been received and closed already, making this an unusually active (but incredibly useful) ongoing review process. Leo and Jeremy also contributed portions of text for the Objects and FFI chapters in alpha6, and join Stephen Weeks as external contributors to the book.

Meanwhile, Leo himself has recovered from the elation of being granted his PhD, to the harsh reality of having to finish corrections. He has been forced by his colleagues to stop hacking on OCaml and submit his final thesis. Rumours are that he will reemerge in June after delivering his SAS 2013 talk on using an implication-algebra generalisation of logic programming to concisely analyse OpenMP programs for parallisation opportunities.

This month's talk was courtesy of Mathias Bourgoin, who visited from France and gave a talk on his PhD work on GPU processing. His tool, SPOC has been released onto OPAM and is a set of easy-to-use tools for generating CUDA and OpenCL code, and also a camlp4 extension to write external kernels directly in OCaml. Thanks for visiting, Mathias!


It's been a heads-down month of hacking at the Labs for April, as the group have settled into their projects and are concentrating on getting code out. We did take the opportunity to redesign the [../tasks/index.html project pages] as the active projects grew.


We welcomed [../people/euan.html Euan Harris] as a new visitor, and he has begun work on a distributed actor library in the vein of Erlang's OTP. The prolific Daniel Bünzli also joined us for the summer to work on his Vg visualisation library. He's based out of the Citrix offices, and is also contributing to the Xen project.

Platform projects[edit]

OPAM The project has entered a bug fixing stage after its release, and the package set has steadily grown via external contributors. David Sheets has been hacking away on the automated [../tasks/platform.html#OCamlot OCamlot] bot, and we released improved Github API bindings. We're aiming to get OCamlot live and running in May, so stay tuned! There is a [../tasks/platform.html#Machine%20Pool steadily growing collection] of odd ARM and PowerPC devices in Anil's desk that will generally make it easier to test your OCaml code in unusual environments. redesign Progress on the website continues and we're now working on the actual HTML/CSS from the earlier mockups. We'll be publishing these in a fork of the website repository, so do feel free to create issues there with your comments. Philippe has begun the [../tasks/outreach.html#Meta%20preprocessor MPP] templating tool to glue together all the website scripts more coherently. Discussions about this take place on the infrastructure mailing list, which is open to all.

Events The monthly OCaml get togethers in the Cambridge Makespace are also really fun. This month saw around 30 people wander through the doors, and work through the latest excerpts of Real World OCaml. And around midnight, Jeremy and Leo competed to find more and more obscure bugs in the corners of the OCaml type system... You can track the subsequent meetups via the NonDysFunctional Meetup group, which includes functional programmers from around the Cambridgeshire area. Jon and Anil also attended the Yahoo Hackday in London, where Jon met a giant robot and started SSL bindings, and Anil experimented with js_of_ocaml LocalStorage for Irminsule.

Systems projects[edit]

Mirage We've finally got a release date for the first preview of Mirage, which will be at O'Reilly OSCON this July! Pulling together the release is a big endeavour, and the [../tasks/mirage.html team] has started weekly calls to work through the project. The minutes for these are online, so you can browse them to catch up. There's also a slightly scary checklist of all the libraries that need to be released before July, so the team has its work cut out for it! The Xen group also announced that it is joining the Linux Foundation, and the become-linux-foundation-collaborative-project press release gave Mirage a prominent mention as one of the key recent developments in Xen.

Irminsule Thomas now has a full implementation of the git file format in his cagit repository, and the interfaces for Irminsule's branch-consistent model are coming together. He gave a demo to the Mirage team, with discussion notes available.

Compiler projects[edit]

Multicore and Concurrency Stephen Dolan's made great progress on bringing up a multicore runtime using thread-local storage, which results in a surprisingly compact diff to the OCaml runtime. We're now moving onto the higher-level bindings to use the parallel runtimes effectively from within OCaml. We also began a wg-parallel working group in order to start figuring out the evolution of the Lwt and Async concurrency libraries.

libffi Jeremy got frustrated by the difficulty of writing safe C bindings, and started the ctypes library, which offers a pure OCaml solution. This even includes managing callbacks across the OCaml/C divide, and uses libffi under the hood to remain efficient and platform-independent. There is the exciting possibility about hooking this library with the [../tasks/compiler.html#Compile time%20meta%20programming compile-time metaprogramming] to eliminate all performance cost, so we're going to spend some time on this project to make it a well-documented alternative to the existing C FFI.

OCaml Talks The OCaml Labs talk series continued with a visit from Francois Pottier and Jonathan Protzenko from the INRIA Gallium research team. Jonathan presented their [Mezzo]( language, which places emphasis on aliasing and controlled access to mutation. This is of particular interest to several of our systems projects that do not require the full power of OCaml to build low-level systems components, and Raphael, Alan, Leo and Anil had productive discussions about how we could try Mezzo out when it's released.



The OCaml Labs hackers continue to arrive, with [../people/sheets.html David Sheets] arriving from sunny San Francisco, and [../people/xclerc.html Xavier Clerc] visiting from the less-sunny INRIA in France. David's done great work on severalOCaml libraries such as Cohttp and on WebGL, and he's diving straight into a first release of [../tasks/platform.html OCamlot] before starting his PhD later in the year. Xavier will work on releasing his OCaml Java 2.0 rewrite this summer, which takes advantage of all the latest JDK features for non-Java languages.


A new research grant has also been awarded to [../people/crowcroft.html Jon Crowcroft]. The Hub of All Things is a £1.2m multi-disciplinary project funded by the RCUK Digital Economy Programme and led by Irene Ng in Warwick. HAT aims to create a home platform, under the user's control, where a market to exchange their personal data for new products and personalised services could exist. The Cambridge piece of this work will use [../tasks/mirage.html Mirage] for embedded systems programming, and Signpost, to enable devices to connect and communicate with each-other across the edge network.

Platform projects[edit]

OPAM OPAM, the popular OCaml Package Manager, recently had its 1.0 release! OPAM has been in development for just over a year, and this is a significant milestone for the project. The OPAM package repository has had over 500 issues, closed over 400 pull requests and now contains over 450 packages (and more than twice that number if you consider that multiple versions are available). This kind of user adoption is a fantastic sign for the OCaml community. We're very happy to be using OPAM as a key piece of the upcoming OCaml Platform and the continuous integration and test system. redesign Amir extended the Balsamiq mockups into more realistic static site designs that can be [ found on the wiki]. We're building on the theme we began with the OCaml Logo, but also including the full functionality we want for the revamped site. The samples should give people an idea of the colour schemes and images we'll be using, and feedback is very welcome. Next, we're creating the HTML/CSS templates we need to make these mockups a reality.

OCamlot Within hours of getting off the plane, David was already getting well into the OCaml-based test tool and working on the pieces we need to get to a usable first version. The OCamlot workflow was last described in Amir's Balsamiq mockups in case you want to catch up. This work is made all the more important as Jane Street continues to demonstrate their strong commitment to open-source by sending in OPAM pull requests every weekfor new releases of their libraries. The testing for these releases is currently handled manually and we're really looking forward to having them dealt with automatically!

Systems projects[edit]

Mirage There is much preparation ongoing for the big incubation, which has now been approved by the Xen community board. Vincent's work on [../tasks/mirage.html Mirari] is going very well, and he's updated the Mirage installation instructions to use Mirari instead of the manual process required before. [../people/avsm.html Anil] and [../people/mort.html Mort] also attended and presented the ASPLOS 2013 paper in Houston. For the curious, Ben's Beans is the only good coffee we could find suitable for a European in Texas.

Irminsule Now that the core of Mirage is heading for release, the team is turning their attention to the storage and distributed programming challenge. [../people/tg.html Thomas] and Anil have been working on a new policy-free, branch-consistent storage layer that exposed a raw git-like universe to Mirage applications. We're working on as part of the [../tasks/t2.html Trilogy2] that's investigating how to improve the reliability of congested datacenters.

Signposts [../people/heidi.html Heidi] gave an excellent talk about Signpost and the benefits it can offer internet users today. This was one of a set of talks that took place in the Computer Lab, organised by [../people/mycroft.html Alan Mycroft], on open software and open hardware with speakers such as Jon 'maddog' Hall) of Linux International. There was fairly unanimous agreement that Heidi's slides were better than Anil's.

Compiler projects[edit]

Multicore Once the dreaded ICFP deadline was out of the way, Stephen, Leo, Raphael and Anil put their heads together to start architecting the support for parallel multicore support in the OCaml runtime. A key part of the design space is to maintain the sequential performance and simplicity of the existing runtime, but still make it easy to extend shared memory onto different cores. We'll have more details on this shortly when early prototypes are done and some benchmarks run.

Namespaces Leo's also been extremely busy in the platform mailing list, which has been the location for the discussion of namespaces. A few hundred emails have been exchanged on this topic and Leo has summarised the discussion and made proposals in his blog post about OCaml namespaces. Although this is a complex issue, aspects of namespaces will be important to the work on the OCaml Platform so we look forward to the outcome of these discussions.



Two new people joined the core team at Cambridge: [../people/yallop.html Jeremy Yallop] and [../people/pwang.html Philippe Wang]! Jeremy has extensive expertise with meta-programming and generic programming, and is initially looking at the [../tasks/compiler.html#Camlp4%20redesign) camlp4 redesign]. Philippe has been taking on the challenge of running OCaml well on restricted embedded systems, which will also have knock-on benefits to x86 compilation with the same optimisations. Xavier Clerc also joined us for a day in advance of his visit in April, with much interest in his Argot project and the upcoming [../tasks/ redesign of].


Two new research grants have been awarded that are relevant to the OCaml Labs mission:

  • Network-as-a-Service is a 3-year grant to solve pressing problems in "Big Data" processing, and will enable us to continue to develop MirageOS and the use of OCaml and functional programming in this space. We're going to be collaborating with Imperial and Nottingham on this, with the Cambridge efforts led by Andrew Moore, [../people/crowcroft.html Jon Crowcroft] and [../people/avsm.html Anil Madhavapeddy].
  • Rigorous Engineering of Mainstream Systems asks how we can use rigorous maths to improve the quality of mainstream computer systems. It is led by Peter Sewell at Cambridge, and most of the tools (including Ott and Lem) are written in OCaml and will benefit from the ongoing work at OCaml Labs.
Platform projects[edit]

OPAM We've been working hard on an OPAM 1.0 release, and Thomas and Anil have been sweeping through the package tree to stabilise the repository via automated builds. We also had a brilliant visit from Roberto Di Cosmo from PPS, who has contributed extensively to the open-source community over the years. He gave a talk on the challenges of handling large-scale versioning of packages from a mathematical perspective (particularly applied to Debian), which is very useful input for the ongoing OPAM work.

Mailing Lists A new was set up for those interested in OpenGL and WebGL on OCaml, and discussion so far has covered LabGL on the Raspberry Pi. There are also still plans to begin working groups for build systems and parallelism but will be announced in due course once the preparatory work has been completed.

Real World OCaml The book is now on alpha3, where Part 1 is nearly complete. New sections on installation and a more expanded prologue have also been included in this version.

Redesign As part of the [../tasks/ redesign work], and to showcase the kind of additional functionality we'd like to create, Amir put together a set of screencasts that talk though a wireframe demo of the new site. These short videos covered elements of design, the new documentation system and an overview of how the continuous integration system would work. You can read more and experience the clickable demo via Amir's blog post.

Systems and compiler projects[edit]

Mirage Anil gave two tech talks about Mirage this month at Citrix and Microsoft Research, as practise talks for ASPLOS 2013. Mirage itself is nearing a release, and Vincent Bernardoff has joined the Citrix engineering team to help drive it to release. He's been primarily focussed on the build frontend (dubbed [../tasks/mirage.html#Mirari Mirari] to make Mirage applications easier to compile out-of-the-box.

Camlp4 redesign There has been more discussion about the future of camlp4 and Leo posted another summary on his thoughts for an alternative approach to quotations.


There's a lot of interest in the work we're doing, and the number of collaborative [../tasks/index.html projects] is increasing fast. We held the first monthly meeting in the Computer Lab, where [../people/avsm.html Anil] provided an overview of the [../tasks/index.html research work] that OCaml Labs is starting. An interesting theme of the discussion that followed was related to undergraduate teaching and how things like the [../tasks/platform.html OCaml Platform] and infrastructure would make it easier for students to get to grips with programming.

For the evening after the meeting, [../people/amirmc.html Amir] set up an informal OCaml hacking/tutorial session in Cambridge. Around 15 eager people attended the event in Makespace (a community workshop), with most of them being new to the language. Anil introduced [../tasks/outreach.html#Book%20review%20site Real World OCaml] and shared the introductory chapters while Thomas provided help with OPAM. This turned out to be a great test of the installation process for newcomers to OCaml, as well as the book's instructions. A number of issues came to light, partly related to a perfect storm of package issues, which everyone is keen to improve. Despite these problems, attendees were very positive and were keen to see more gatherings like this in future. When Amir asked for feedback, pretty much everyone commented on how great the pizza was.

Platform projects[edit]

OCaml Labs also hosted its first visitor this month as [../people/tg.html Thomas Gazagnaire], the CTO of OCamlPro, spent three weeks in Cambridge. Much effort was put into preparing Mirage for release, discussions about parallelism and the OCaml Platform, and anything where OPAM is a crucial component. Worth noting is that (at time of writing) the opam-repository has now become the overall most forked OCaml project on Github. The Platform mailing list has also been formed for discussion regarding the OCaml Platform. Anyone interested in the discussions about the platform, which will include development on OPAM, should join this list.

Part of the Platform work involves creating a new [../tasks/platform.html design for], which also kicked-off this week. Amir will keep people updated about progress via updates to the [../tasks/ OCL website], Infrastructure mailing list and also by posting things to the Github wiki. The current stage of work involves thinking of the types of pages requires, in order to refine the templates we need. As part of this, we also commissioned a new logo for OCaml and although it's still under development, you can see the latest draft on the wiki. Please send any feedback directly to Amir.

The Real World OCaml book website was released as a limited alpha earlier in the month, with the aim of getting early feedback and comments. Each paragraph of the online book has commenting functionality, using Github issues as a backend. This means that each comment made on the book website creates a new issue on Github, which authors/commenters can track and discuss before editing the content. So far there have been over 250 comments on the alpha, with half them being dealt with already.

A new EU project also kicked-off called [../tasks/t2.html Trilogy 2], which builds on the award-winning work from the original Trilogy project. OnApp (a member of Trilogy 2), will be providing the cloud Infrastructure for, and Thomas and Anil will be expanding the Mirage project into distributed computing under this umbrella. As befits an EU project, it kicked off with an especially nice dinner at Christ's College...

Systems research[edit]

Mirage This was formally proposed as an [../tasks/mirage.html incubated project] and the proposal was put forward for community review. There were many positive comments on the Xen mailing lists (along the lines of "Mirage is cool stuff") and voting is currently underway by eligible members of the Xen community. Assuming a positive outcome, incubation would give the Mirage project greater visibility and access to resources. This would accelerate progress towards an alpha release in Q1/Q2 this year. In addition to this, a proposal for an OSCON talk was also submitted and the camera-ready version of the ASPLOS paper is now available.

Illuminate A related research topic where Mirage could be useful is in embedded systems and the Internet of Things. One specific use case is the [../tasks/illuminate.html Illuminate Project], where Mirage can be used to create appliances running on the ARM microcontrollers alongside an LED lighting network. Such a lighting system is now deployed in large parts of the Computer Laboratory and will form an excellent test-bed to explore these ideas further.

Signpost Signpost is also achieving greater outreach with [../people/crowcroft.html Jon Crowcroft] discussing such technologies at a meeting in Dagstuhl on Decentralized Systems for Privacy Preservation. Cambridge also hosted Eric Schmidt from Google, where he is the Humanitas Visiting Professor in Media for 2013. Eric delivered a talk on the future of conflict, combat and intervention. Anil and Jon got an opportunity to discuss Signposts with him for 20 minutes, which was an interesting clash of opinions (we want decentralised identity, Google want it all to go through them). Either way, we're even more motivated to get the Signpost tech out to the big bad world as soon as possible. Meanwhile, Haris found his identical twin brother in St Johns Masters Lodge...

Compiler projects[edit]

Several mailing lists are in progress for various community-driven projects. The first of these is a working group on the future of syntax extensions in OCaml (wg-camlp4). This group is chaired by Alain Frisch and Leo White and has generated a great deal of discussion in the last two weeks. Leo is summarising his thoughts in a series of blog posts as he goes. Further working groups on parallelism in OCaml and build systems are under discussion and will be announced in due course.

As well as all the research and development activity we've also been recruiting. We've had several rounds of interviews and made a number of offers so hopefully we'll be announcing new members of the OCaml Labs team in the coming months. In addition, we'd also like to mention that Leo successfully defended his PhD Thesis in January. Finally, we'd like to welcome a new honorary member of OCaml Labs, Nathan Scott, born on 30th January. Congratulations [../people/djs.html Dave]!


OCaml Labs kicked-off with an internal meeting of the Cambridge-based members, who battled endless snow to make it to the meeting. There are over 20 people involved just within the building and over 30 including those outside the University. We welcomed a few new members, including Leo White (Postdoc), Raphael Proust (PhD student) and Stephen Dolan (PhD student). At this initial gathering Anil talked over some of the projects that were already taking place in the Lab, as well as the new work that would be supported by OCaml Labs.

Significant progress was made on the research side too. [../tasks/mirage.html Mirage] has had a flurry of new releases as we prepare for a first public release, and we're in the final stages of being officially incubated as a [../tasks/mirage.html project]. [../tasks/illuminate.html#Signpost%20prototype Signpost] is also taking shape, mainly due to the addition of DNSSEC to the [../tasks/illuminate.html#Signpost%20prototypew ocaml-dns] implementation. There's been industrial interest in the applications of Signpost and the team is pursuing these for more use cases.

We also began work on a new website for the Real World OCaml book. We took inspiration from our friends who wrote Real World Haskell, and the site will have commenting functionality so that people can suggest improvements before the book is finalised. As part of this, we also worked with a design firm to begin creating a [../tasks/ new logo for the OCaml language].The logo will be placed into the public domain for use by anyone.

Last, but certainly not least, Ashish put the new website live, to much electronic applause.

A great way to end 2012!


OCaml Labs finally opened its doors with announcements from Yaron and Anil! Although much of the remainder of November was spent on administration and wiring up machines for the forthcoming [../tasks/platform.html#Machine%20Pool test cluster], we also celebrated the acceptance of a paper on [../tasks/mirage.html Mirage] to ASPLOS 2013.

We also had a very productive visit from OCamlPro. Fabrice, Thomas and Pierre came over to discuss the new OPAM package manager and the plans for building an OCaml Platform in 2013. This was in preparation for the subsequent Consortium meeting of the industrial board of OCaml, where Anil was able to present (and get approved) an overview of what would become. You can see the slides of his talk online. An interesting thing to note is just how broad the set of OCaml language users are: right the way from formal methods, to systems projects, and even web developers.

Since the Consortium meeting, the infrastructure behind is being built out and there's already been helpful input via the infrastructure mailing list. A continuous build system has been put together for internal testing, with support from Citrix, and OPAM itself continues to mature and grow in popularity.