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From: Jesper Louis Andersen <jesper.louis.andersen@gmail.com>
Date: Sat, 8 Jan 2011 10:44:43 +0100
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To: David Rajchenbach-Teller <David.Teller@univ-orleans.fr>
Cc: Damien Doligez <damien.doligez@inria.fr>,
        Dario Teixeira <darioteixeira@yahoo.com>, caml-list@inria.fr
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Subject: Re: [Caml-list] Purity and lazyness

On Fri, Jan 7, 2011 at 17:38, David Rajchenbach-Teller
<David.Teller@univ-orleans.fr> wrote:
> Correct me if I'm wrong, but I wouldn't classify Erlang as "pure": sending and receiving messages -- which are two of the most important primitives in Erlang -- are definitely side-effects.
> Also, asynchronous error-checking, Mnesia, etc. look quite impure to me.

Right.

Erlang with only the sequential primitives present is not pure either.
There is a process_dictionary which is essentially a state for the
process. Erlang programmers tend to avoid it, but it is used by some
of the standard libraries. Keeping random seed state for instance. If
you remove the process dictionary, then there is ETS, the erlang term
storage (in use as the backend for mnesia). ETS is not pure either, it
is essentially a finite map from erlang terms to erlang terms. Ok,
strip out ETS. Then we have exceptions :) Exceptions are, to the best
of my knowledge, yet another computational effect.

And then there are all the concurrency primitives...

-- 
J.