Together with PhD students Christophe Scholliers and Dries Harnie, I recently completed an operational semantics of our AmbientTalk programming language. We believe this is the first formal account of an actor language based on communicating event loops. The paper is currently available as a techreport. From the abstract:

We present an operational semantics of a key subset of the AmbientTalk programming language, AT-Lite. The subset focuses on its support for asynchronous, event-driven programming. AmbientTalk is a concurrent and distributed language that implements the so-called communicating event loops model.

Christophe has written an executable version of the operational semantics in PLT Redex. You can read all about that here.

The operational semantics builds on that of a similar model, JCobox, but significantly adapts it to more accurately reflect the semantics of AmbientTalk’s futures, which are based on E’s promises and are entirely non-blocking. And unlike JCoBox, AmbientTalk does not support cooperative multitasking within an actor, only purely sequential, run-to-completion execution of incoming messages, much like a Javascript per-frame event loop.

For the past two years, I have been working on a new Reflection API for ECMAScript (the Javascript standard) together with Mark Miller. Its most novel feature is its support for proxies, objects whose behavior in response to a large number of built-in functions and operators can be controlled in Javascript itself.

Last week, I finally finished a paper that not only describes the new API in some detail, but also describes the principles that helped steer our design. From the paper’s abstract:

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Update (July 2015): Proxies are now officially part of the recently released ECMAScript 2015 specification. This tutorial is still relevant, but dated. For up-to-date documentation, see e.g. Mozilla’s MDN page on proxies.

The Proxy API enables the creation of dynamic proxies in Javascript. Dynamic proxies are useful for writing generic object or function wrappers or for creating virtual object abstractions. To avoid any confusion: these proxies have nothing to do with web proxy servers.

Perhaps the most compelling use of proxies is the ability to create objects whose properties can be computed dynamically. Proxies encompass all use cases that one would use the SpiderMonkey hook noSuchMethod for (such as creating mock objects in testing frameworks, Rails ActiveRecord dynamic finder-like capabilities, etc.) but generalize to operations other than method invocation.

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When I present my research work on programming languages, people often ask me “why do you need a new programming language to solve this problem? Why not just implement it as a library?” Or, I get asked “why didn’t you implement it as an extension to {some existing language}?” In this essay I will try to make explicit some of the goals and motivations behind language design. They are formulated wholly from my own background in this area, so I might be missing some important ones I haven’t thought about.

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Last July, I presented AmbientTalk at the first Emerging Languages Camp at O’Reilly’s OSCON in Portland. The talk was well received and AmbientTalk got some media coverage, among others an article in Technology Review Magazine and an article in Data News (in Dutch). Dean Wampler posted a good summary of all discussed languages (including AmbientTalk) on his blog. After the conference, I was interviewed for Microsoft’s Channel 9 together with Mark S. Miller, Jonathan Shapiro and Gilad Bracha. It’s a very impromptu interview, covering topics like static typing, mirror-based reflection and AmbientTalk’s interoperability with the JVM.