Hackable scheme implementation with decent C++ FFI

I have tried: scheme48, chicken, gambit, clojure.

I am looking for a scheme implementation that's readable (the implementation itself), and has a decent C++ ffi, and good debugging suport (so when I get an excep开发者_运维问答tion, I should get popped into a recursive repl).

What suggestions do people have?

MzScheme. It can be embedded in C/C++ programs. It can be extended with C libraries, with no special interfacing code. Checkout "Inside PLT MZScheme" for detailed documentation.

s7 scheme has worked well for me. It is in a single .c file and has a nice foreign function interface.