[erlang-questions] Erlang and Akka

[Jesper Louis Andersen]

On Wed, Aug 27, 2014 at 1:53 PM, Ulf Wiger <ulf@REDACTED> wrote:

> - Software quality: Immutability basically goes together with referential
> transparency, and you should aim to write as many functions as possible in
> a side-effect free way. Once such a function has been debugged and works
> correctly, it *stays* correct, until the requirements change. For this
> reason, legacy Erlang code can truly become rock-solid.


I've had the same experience in three projects now of larger size:

Once your Erlang system is up and running and you weeded out the most
glaring bugs, the system becomes rock solid. In all three projects, the
requirements are set in stone and won't change right away[0]. All three
systems has been running for months now, with no intervention. And they all
process around 20-30 requests per second. One particular system has been
doing this for over a year without any intervention, no reboot. Subsystems
around the Erlang systems have died left and right, but the Erlang-systems
themselves do not care about such misbehaviours. They automatically recover
once the subsystems become healthy again.

I have a hunch that this property is also making Erlang programmers more
productive: Once your system is written, there is very little to maintain.
So your programmers go off and does more productive stuff. In a world where
the system keeps failing, you reset the programmer back to that system
again and again. This hampers productivity in the long run.

[0] This is one of the ways you know you got the design right. You can
isolate the parts of the system which has to change from the parts of the
system which don't. When this works, things fall out really well usually.
Everything hinges on getting the specification right so you can figure out
what parts of the system needs to change going forward. And then
freeze/lock down the parts that don't, preferably with property based
testing.

-- 
J.
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