I had tried this with python a while ago. Simply translating python code into C code using the objects in Python/C API gave up to 30% speedup. However, that is not much, considering the fact that python is up to 100 times slower than C. For speedups that are more significant, you really need type inference.
This reminds me Cython who provides optional types to speed up the critical path. The speed gains are pretty impressive.
Having a such tool in Ruby would be wonderful !
Did your experiment still do dynamic calls where Python would do dynamic calls? fastruby does not; all dynamic calls are converted into Java virtual dispatches, which optimize and inline like normal Java code.
The 30% improvement I got on "fib" was not as much as it would be for inferring the actual numeric types, but that's indeed possible here too. You should also keep in mind that the resulting code was by definition as fast as Java code would be doing the same work (i.e. all boxed math) so anything not math-related would actually be Java speed too.
