What I wonder is whether the Chez base might massively improve Racket's concurrency capabilities.<p>In Common Lisp, one has pthreads-like concurrency capabilities which seem very well suited for fine-grained parallelism as well as for server tasks. I am thinking in such things like parallel backtracking and optimization algorithms for robotic control or board games, for example.<p>However, threads are notoriously difficult to handle cleanly and safely in larger programs. Here, Clojure (which in my eyes is a very Scheme-like Lisp) offers a very elegant solution with its concurrency primitives of Futures, Atoms, Agents, and STM. After some experimenting, I believe they are very, very attractive for many concurrent server tasks (like a web server), but not that well suited for computing-intensive parallel algorithms like the ones I mentioned above, which I am highly interested in. Part of the reasons are that such algorithms can become quite GC-heavy. Also, the Clojure compiler has limits on how much primitive types can be passed as parameters in one functions. This means that a complex backtracking algorithm in Clojure can still be two orders of magnitude slower than in C (which is somewhat disappointing, but one has to remember that Clojure was not designed for this).<p>Racket has had, so far, only limited concurrency capabilities. It had Futures, however they could easily become blocked by GC. It also has Places, which are a very safe and clean solution of splitting parallel computations into separate processes. However, I think that places are not the first choice for heavily parallel algorithms with strong interdependencies.<p>Now, Racket can run on top of Chez, and Chez has fine-grained concurrency capabilities on top of pthreads, which seem to be on par with Common Lisp. Also, Racket has strong support for functional and side-effect free programming, including some data structures. In my impression, this seems to open a wide range of new possibilities, including providing look-alike primitives for Clojure's Futures, Agents, and Atoms. I would be very interested to know more whether this impression is correct.