These are some implementation details that are still subject to change:
I’m leaning towards making the initial Spark implementation use Parrot as its virtual machine. LLVM was suggested, and while it seems nice and powerful, it requires the compiler front end to be written in C/C++ which will cause the time to market to grow considerably. I don’t rule out a later implementation of Spark to LLVM, but during the initial implementation we would like to change things rapidly and quickly, and C or C\++ will slow us down considerably.
I’m not keen on using the Java Virtual Machine, due to Java’s long historical reputation of being “enterprisey” and non-hacker friendly (see http://www.paulgraham.com/javacover.html ), and due to the fact it has a slow startup time, and that it feels very “sluggish”/non-responsive. Again, I don’t rule out a future port of Spark to the JVM.
The Parrot VM seems very suitable for dynamic languages, and it is progressing nicely. The Parrot languages Page already lists several implementation of Scheme which can serve as the basis for a Spark implementation, so I’d like to start there.