[pizlonator]

It’s true that the Fil-C approach focuses on having a memory safe userland with no exceptions, which means no FFI to unsafe code (aside from the Fil-C runtime itself, which is just syscalls wrappers and a small handful of other things).

I have considered what FFI to native could look like, and have so far rejected it because it hurts the “no unsafe code” purism.

You’re right that this limits me to those OSes where the syscalls themselves are an adequate ABI. Linux isn’t the only such OS. It just happens to be the only OS Fil-C supports right now.