Yes and no. Some language features can make it incredibly difficult to optimise. I know the JRuby folks had all sorts of fun trying to make method dispatch fas

Yes and no. Some language features can make it incredibly difficult to optimise. I know the JRuby folks had all sorts of fun trying to make method dispatch fast in the face of "well, this method definition can be changed at any time, arbitrarily often, including during execution of the method itself". I know CL must also have solved that problem but I presume the toolkit is sufficiently different that the techniques just don't map.