pub fn execute<C>(&mut self, mut continuation: C) -> Result<(), ()>

    pub fn execute<C>(&mut self, debug_mode: bool, continuation: C) -> Result<(), ()>

        // If `debug_mode`, respect breakpoints
        _ = debug_mode;
        _ = continuation;

            let Some((inst, inst_ptr)) = self.mem.mutate(|mc, root| {

            let Some((inst, inst_ptr)) = self.mem.mutate(|_mc, root| {

                                    _ = prim;
                                    _ = arguments;