RbCl: A Re ective Object-Oriented Concurrent Language without a Run-time Kernel

We propose a re ective object-oriented concurrent language RbCl which has no run-time kernel. That is to say, all the behavior of RbCl except for what is restricted by the operating system and hardware can be modi ed/extended by the user. RbCl runs e ciently in a distributed environment and is intended for practical use. The execution of an RbCl program is performed by a metasystem that consists of metalevel objects. All the features of RbCl including concurrent execution, inter-node communication, and even re ective facilities themselves are realized by the metalevel objects, which are modi able and extendable. Important metalevel objects are called system objects, that are registered in system object tables. The user can change the behavior of the metasystem by replacing elements of system object tables with user-de ned objects. RbCl also provides a novel feature called linguistic symbiosis for metalevel objects. All the metalevel objects in the initial RbCl metasystem are actually C++ objects, but the linguistic symbiosis enables the user to manipulate metalevel C++ objects just as ordinary RbCl objects. Even re ective schemes and facilities themselves are realized by system objects that can be modi ed/extended by the user. Therefore, debugging of re ective programs and experiments on re ective schemes and facilities can be expressed and performed within the RbCl language framework. In Appendix, we present a full program list of Rscheme, which is a kernel-less language on Scheme based on a re ective architecture modeling that of RbCl.