I can imagine a fairly clean mapping between languages. If the result of compilation was JavaScript code, to be passed on to the browser using eval(), the code

I can imagine a fairly clean mapping between languages. If the result of compilation was JavaScript code, to be passed on to the browser using eval(), the code would perform quite well. So, assuming that I'm correct, what you would be left with is the one-time cost of parsing. And how costly is parsing generally? (I am keeping in mind that Ruby may not be general)