Have a look at http://t3x.org http://t3x.org There are lots of small, comprehensible compilers and interpreters there, and there is an interpreter and runtime

Have a look at http://t3x.org http://t3x.org There are lots of small, comprehensible compilers and interpreters there, and there is an interpreter and runtime construction kit, look for "S9 core" in http://t3x.org/s9fes/ http://t3x.org/s9fes/. You can also order books explaining all the stuff. And yes, I'm the author! :)