Looking at the first page, I notice they've copied Ruby's system of having separate interpreters for interactive use and scripting use. I don't know much about Ruby, but I know Python quite well and I know it gets along quite well with having only one interpreter. Is there any technical reason why having two interpreters is a good idea?

Eh? Ruby has one interpreter. It also comes with an interactive shell called IRB, written in Ruby. Reia works the same way.

    module Fibonacci
      def simple(0)
        0
      end
      def simple(1)
        1
      end
      def simple(n)
        simple(n - 1) + simple(n - 2)
      end
    end

Ruby style syntax for this example seems too verbose when you consider the succinctness of:

    fib(0) -> 0;
    fib(1) -> 1;
    fib(N) when N > 0 -> fib(N-1) + fib(N-2) .

Very true, but the appeal, to me, of Reia is better string/regex support than currently available in Erlang.

At least that was stated in their goals somewhere, and admittedly my Erlang-fu is fairly weak, so I could be missing something awesome in that area.

I think it's a general consensus that Erlang does not handle dealing with strings very nicely. If Reia can abstract those problems away then it will probably gain a lot of traction. Probably much more than Lisp <del>For</del> Flavoured Erlang, unfortunately.

I'm on the mailing list for the development of Reia and I've been watching progress with some interest. There's already a web framework being built (Ryan) so once the language becomes fully usable I think this'll be a very interesting language.

The one thing that worries me is how much Erlang will still be required. Reia is turning out to have a very Ruby-like syntax, so it should be easy to pick up, but having to learn Erlang as well would give me second thoughts.

I've been a Ruby guy for years and I loved Erlang right away. It's a splendid language.

It's going to be a while before Reia can completely abstract the OTP platform so if you want to work with it any time soon, learn Erlang.

Instead second thinking learning Reia and Erlang, just go learn Erlang. Erlang is finished and has a web framework today.

Or go LFE

http://github.com/rvirding/lfe/tree/master

While it's true that Erlang is a production ready language from many years now and it may make more sense to learn that language, it's also true that these projects helps people realize that it's possible to build other languages on top of the Erlang virtual machine.

Reia is going to be a much better fit for web scripting than Erlang. I'd prefer to use it over Erlang where possible.