Hacking language syntax

Hello, Internals! I wish to add some syntax to PHP (at first, I want to modify while loop, to implement Dijkstra loop) and I've found some old thread about modifying core, but I have no idea, how to do it by extension. I suppose that it possible, since Facebook, as I know, introduced some constructions in its HipHop. But HipHop is rather complex and aimed to do incredibly more things, rather than add one construction, so it's rather hard to study. I'll be glad if someone tell me what to look at for implementing new constructions as an extension. P.s. Please, cc me on reply. -- Best wishes and have a nice day, Vsevolod Velichko