My Google SoC project was writing a c++ bindings generator for Common Lisp: https://lwn.net/Articles/147676/ (In my head this was ten years ago, but apparently it‘s nearing 17. Shit I’m getting old.)

C isn’t ideal, but it’s actually not so bad and it could be worse (it could be C++). Yes parsing C is non-trivial, but that’s true of every language. These days you have libclang and a dozen other decent C parsers. Back in my day we had to use a hacked up version of GCC (and we liked it).

Also, C doesn’t have a standard ABI, but every real world platform defines a C ABI. And it’s pretty simple. Meanwhile trying to handle all of the cases of C++ vtables took up weeks of my life (and I ended up shipping without fully supporting multiple inheritance, which is stupid anyway).

The bigger problem for writing FFIs is, in my opinion, memory management. That’s where it gets really hard to paper over for the binding user that you’re talking to C.