pub type LumenFn = unsafe extern "C" fn(argc: c_int, argv: *const LumenValue, user_data: *mut c_void) -> LumenValue;Expand description
Signature of an exposed callback. argv is borrowed for the
duration of the call; the returned LumenValue (and any pointers
it carries) must stay valid until this function returns - Lumen
copies into a Dynamic before unwinding.