High Level Languages for Prototyping

I want a high level language to try out ideas. Often the ideas I am interested in draws on things such as concurrency, symbolic computing, pattern matching, etc. I don't need a production capable language. This is just for fiddling around with -- a prototyping language if you will.

Tcl and Awk were my prototyping languages of choice for the past 10-15 years. Before that it was Forth and a little bit of Lisp.

However, I have found that I have five criteria for such a language now. The first three are firm, the last two are desired qualities:

1. Supports concurrency (lots of little processes/tasks) seamlessly.
2. Seamless support for Bignums. I don't want to think about silly limitations of native word sizes.
3. No fencing in (multi-paradigm support is a must!)
4. Interactive. I don't want to do a edit/compile/run cycle for simple things.
5. Portable. I want to install it everywhere.

Erlang comes to mind, but it fails for #3.

Logo is nice, but has too many incompatible variants. StarLogo meets #1, but it looks too busy (especially StarLogo TNG).

Item 2 sounds a bit ridiculous, but for languages that aren't bound by performance needs, I don't see why I should be trapped in 32/64 bits. I'll never forget the time, back in 1984, when I typed (fact 120) in Lisp.... oooh.

I've been meaning to learn Mozart/Oz ever since I read CTM a few years back. It's a wonderful book. Maybe if I concentrate *real* hard and drop my other CFT projects, I could pick it up again. :-)