“Syntax Matters”

Compare the following code with the one in the previous post (they do the same thing):

    parallel/or do
        loop do
            await 250ms;
            emit Leds_led0Toggle();
        end;
    with
        loop do
            await 500ms;
            emit Leds_led1Toggle();
        end;
    with
        loop do
            await 1000ms;
            emit Leds_led2Toggle();
        end;
    end;

 

I realized that syntax really matters after teaching Céu as an alternative to nesC in two courses this year.

The new syntax is more verbose and less flexible, but way more readable.

 

A “down to earth” reactive language: Céu

It has been more than one year since my last blog post. The reason is the direction I took two years ago, in the beginning of my PhD, switching from LuaGravity to something more grounded.

LuaGravity was very fun to work with, it showed how reactive languages are expressive, allowing complex dependency patterns to be written with simple expressions. It also showed how easily Lua can be hacked in runtime to provide a completely different semantics.

However, LuaGravity is overly powerful as a research artifact. In this context, what really matters is to understand the motivations, goals, and what is needed  and not needed in a reactive language. The border between Lua and LuaGravity was unclear and Lua is too dynamic, what complicates the deterministic execution enforcement we wanted to provide.

The development of a new language—Céu—is the process to answer and pose research questions related to reactive languages.

Céu can be defined in keywords as a reactive, imperative, concurrent, synchronous, and deterministic language. The syntax is very compact (resembling CSP or Pi-calculus), what is great for writing papers and discussing programs, but not necessarily for developing applications.

Currently, Céu is targeted at Wireless Sensor Networks, but any constrained embedded platform is of our interest. Follows a “Hello World!” program in Céu  that blinks three leds, each with a different frequency, forever:

(
    ( ~250ms  ; ~>Leds_led0Toggle)*
||
    ( ~500ms  ; ~>Leds_led1Toggle)*
||
    ( ~1000ms ; ~>Leds_led2Toggle)*
)

.

I presented Céu in the Doctoral Colloquium [1] at Sensys’11 last week. The 3-page summary submitted to the conference can be reached here.

[1] http://www.cse.ust.hk/~lingu/SenSys11DC/