[tadeuzagallo]

`extern` means it's implemented in native, but it has to conform to the interface that the VM provides, and register that function with the VM. At runtime, the parser knows when a function is local (i.e. in the bytecode) or extern (i.e. C++). If it's local, it'll jump to the function's offset in the bytecode, if it's extern, the interpreter will use a native call.

You can take a look at some native functions here: https://github.com/tadeuzagallo/verve-lang/blob/master/runti... And the implementation for the `op_call` opcode here (notice it has 2 branches: op_call_builtin and op_call_closure, the former is for `extern`ed functions): https://github.com/tadeuzagallo/verve-lang/blob/master/runti...