The Synchronous Blog

A blog about reactive programming languages.

Esterel: A Unique Language

with one comment

Esterel was developed in the early ’80s in France in parallel with other two languages, Lustre and Signal. These, together with Statecharts, are considered the first synchronous languages.
Esterel found its niche in control intensive real-time applications and evolves as a standard, with several implementations.

Unlike all synchronous languages, Esterel is the only one to provide an imperative style of programming. This is kind of surprising for me considering the high popularity of imperative languages.
Why there’s no attempts to create new languages based on the Esterel foundations?

I cannot argue about functional vs imperative style of programming, but I do feel more comfortable with the latter (most people do), and they will be around for the next years.
I like the Lua approach, which seems to favor imperative style but concisely support most functional features without bloat.

The example below, written in Esterel, implements the basic training for an athlete:

module Runner:
    input  Second, Morning, Step, Meter, Lap;
    output ...; % not used
    every Morning do
        abort
            loop
                abort RunSlowly when 15 Second;
                abort
                    every Step do
                        Jump || Breathe
                    end every
                when 100 Meter;
                FullSpeed
            each Lap
        when 2 Lap
    end every
end module

Esterel authors argue that, following this imperative style, programs are almost software specifications given as recipes in natural English.

The communication in Esterel is made through broadcast input and output signals.
The synchronous preemption constructs (every do, loop each, abort when, etc) are the heart of the language.
LuaGravity provides constructs based on them, which I consider even more useful than the functional facilities.

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Written by francisco

September 29, 2008 at 11:01 pm

One Response

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  1. […] supports reactivity inside its methods in some way like Esterel does. The AWAIT primitive suspends the execution of a method and waits for another method (or […]


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