Does anyone else have experience with TeX? Knuth wrote it in Pascal (I was there when he was considering whether Pascal or C would be the right choice), but most implementations run as C. Someone wrote a set of support routines plus a translator for the very restricted Pascal that Knuth used. Local modifications to the code are almost all handled by substituting new Pascal code which is incorporated by a preprocessor before being translated into C. Really works pretty well, and some of the same techniques should carry over to pypy.

I once started a project to translate TeX to Java, but found the translation to Java more difficult than that to C and ended up abandoning it.