Lambda the Ultimate

Ruby and python have been mentioned many times on LtU, but I would like the opinnion of gurus here. Which language is more interesting for those who have deeper knowledge of programming language theory?

I'm not so concerned with speed of respective VMs, the community around these languages, even their syntax, etc. I'm iterested in the languages (and their APIs I suppose).

For example, for practical programming, are ruby's continuations significantly better than python's co-routines (2.5)? How do 'lambda' functions in each language compare?

Is one language closer to 'functional' programming than another? Is one language better than another for building logic programming or constraint logic programming constructs? Is one language better than another for building the kind of functionality found in concurrent languages (erlang, Oz)?

Lee, E.A., "The Problem With Threads", IEEE Computer, vol. 36, no. 5, May 2006, pp. 33-42, available online as U.C. Berkeley EECS Department Technical Report UCB/EECS-2006-1

For concurrent programming to become mainstream, we must discard threads as a programming model. Nondeterminism should be judiciously and carefully introduced where needed, and it should be explicit in programs.

Many of the points about concurrency raised in this article will be familiar to LtU readers, particularly those who have any familiarity with CTM, but the article does provide a good summary of the issues. Beyond that, what I found interesting (especially from a PLT perspective) is Lee's contention that the emphasis on developing general-purpose languages that support concurrency is misplaced. Lee believes that a better approach is to develop what he calls "coordination languages", which focus on arranging sequential components written in conventional languages into some concurrent configuration (I suppose that piping in a Unix shell could be considered a limited coordination language). Quoting from the article:

"Coordination languages do introduce new syntax, but that syntax serves purposes that are orthogonal to those of established programming languages. Whereas a general-purpose concurrent language like Erlang or Ada has to include syntax for mundane operations such as arithmetic expressions, a coordination language need not specify anything more than coordination. Given this, the syntax can be noticeably distinct."

It's not immediately obvious to me that there's anything preventing a "coordination language" from being a well-defined subset of some more general language. Lee's key point seems to involve making coordination constructs syntactically distinct (e.g. block diagrams vs. text). Which, of course, raises some interesting questions about whether other important facets of a language (such as the language of type declarations) should also have strongly syntactically-distinct representations, and just how homogeneous (Lisp anyone?) the syntax of a language should be...