I wrote a PHP-&#62;C++ compiler and bits and pieces of the standard library many moons ago (BinaryPHP: <a href="http://sourceforge.net/projects/binaryphp/" rel="nofollow">http://sourceforge.net/projects/binaryphp/</a> ), and it really wasn't terribly difficult, even for a complete compiler novice.  We didn't do the fancy optimization that HipHop does, but it worked fairly well at the time.  The actual compiler would probably only take a month or two (disregarding real optimizations) for a talented developer or two, but the runtime (assuming it doesn't share anything with PHP proper -- don't know if this does or not) would take much, much longer.<p>Doing it for Ruby or Python would be fairly straightforward to get running initially, but doing Perl&#60;=5 would be impossible (for all cases) due to it being proven impossible to statically parse.