[erlang-questions] suitability of erlang

Ulf Wiger <>
Thu Oct 11 16:44:05 CEST 2012

On 11 Oct 2012, at 16:17, Rustom Mody wrote:

> I have one more question that sits somewhere between parallelism and concurrency.
> In the 'normal' world (ie C++, Java, Python) there is a general recommendation that converting a threaded solution to an event-driven solution usually speeds up the program and removes hard-to-find bugs.
> And at the heart of an event-driven system is usually an FSM.
> Now I am particularly interested in the combined (regular-exp+FSM) approach that ragel provides:http://www.complang.org/ragel/
> In particular, here is the use of ragel to write an http server: http://www.zedshaw.com/essays/ragel_state_charts.html
> Now since ragel is more or less language agnostic -- it has backends for generating C, C++, Java, Ruby etc -- would an Erlang backend for ragel make sense?

As far as I can tell, Ragel is mainly for parser FSMs. As such, it seems
great, but I doubt whether it would add value to Erlang as a way to 
specify concurrent (message-passing) state machines.

The thing it lacks that Erlang has, is selective message reception.
This allows Erlang to ignore a message in its inbox, and keep waiting
for the desired message. In coordination problems, this is a great 
way to avoid complexity explosion.

I gave a talk about that a while ago:


Basically, you _could_ generate Erlang FSM code from Ragel code,
I'm sure, but I think this would mainly be useful for porting existing
Ragel models over to Erlang. Ultimately, I think it would still be better
to do the 'porting' by hand, to give you a chance to think through the 
problem in a more Erlang-ish style.

The FSMs that are easy to write in Ragel, also ought to be easy to
write in Erlang.

If I missed some clever device in Ragel that handles this, please 
correct me.

Ulf W

Ulf Wiger, Co-founder & Developer Advocate, Feuerlabs Inc.

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