An abstract machine design for lexically scoped parallel Lisp with speculative processing

An abstract machine is designed to support the data environment requirements of BaLinda Lisp, a parallel Lisp dialect which permits speculative processing of conditional modules. Logically, the machine provides multiple stacks connected into an environment tree, with lexically visible sections pointed to by display registers. Physically, stack sections are stored as separate objects and access is established by the use of a dynamic stack recording the chain of function calls, and a set of lexical display registers pointing at visible objects. This arrangement allows parts of the environment of a function to be retained or garbage-collected as appropriate after exit. By making copies of visible ancestral stack sections, side effects of speculative parallel tasks are handled in accordance with language semantics. The architecture is generic and may be realized in a variety of forms, depending on whether BaLinda Lisp is implemented on a conventional machine, stack machine, or dataflow machine.