Scheme is deceptive. I think R5RS was all of 50 pages or so. But try implementing quasiquotes, closures, lexical scoping, tail call optimization. Not to mention

Scheme is deceptive. I think R5RS was all of 50 pages or so. But try implementing quasiquotes, closures, lexical scoping, tail call optimization. Not to mention the trickier things of call/cc, dynamic-wind, hygienic macros. There is a surprising amount of complexity involved. Even if you do go with the simplest of GCs, which is probably stop-and-copy.