The Interlisp Virtual Machine Specification

INTERLISP is an interactive LISP system. It consists of a large and sophisticated collection of user support facilities (such as DWIM and the Programmer's Assistant [TEl]) built on top of a fairly conventional LISP language. We call this underlying conventional language "Virtual Machine" (or simply VM) LISP. The user support facilities are written entirely in VM LISP, and are in the public domain. Thus, if VM LISP is implemented on some machine, the rest of INTERLISP can be obtained from publicly available files1. Although the INTERLISP System is extensively documented at the user level in the INTERLISP Reference Manual [2], it is not possible to implement the system from that documentation. The purpose of this document is to specify VM LISP as fully as possible from the implementor's point of view. Consequently, this document emphasises clarity and conciseness over intuitive appeal. It is expected that a prospective implementor will have access to the INTERLISP Reference Manual for explanations of the justification or implications of certain specifications. Furthermore, since its purpose is mainly a practical one (i.e., to tell an implementor what must be done), the document is not altogether formal. Because INTERLISP evolved under the rather sophisticated BBN TENEX2 time sharing system, it assumes the presence of capabilities (such as user-defined interrupt characters) which may not be found in the implementor's environment. If an implementor is forced by such circumstances to forego the implementation of certain INTERLISP features, the user-support facilities may not perform as described in the Reference Manual. The implementor assumes responsibility for the documentation of such deficiencies. A great deal of care has been taken in the preparation of this document to determine the assumptions made in the high-level facilities about features in the underlying VM. Because of the size and complexity of the system we cannot guarantee that we have identified them all, and therefore do not assure the prospective implementor that the rest of INTERLISP will run perfectly upon loading it into the just implemented VM. However, this document goes a long way toward that admirable (and probably impossible) goal.