Overview of a Display-Oriented Editor for INTERLISP

DED is a display-oriented editor that was designed to add the power and convenience of display terminals to INTERLISPs teletype-oriented structure editor. DED divides the display screen into a Prettypnnt Region and an Interaction Region. The Prettypnnt Region gives a prettyprinted view of the structure being edited; the Interaction Region contains the interaction between the user and INTERLISPs standard editor. DEDs prettyprinter allows ellision, and the user may zoom in or out to see the expression being edited with more or less detail. There arc several arrow keys which allow the user to change quite easily the locus of attention in certain structural ways, as well as a menu-like facility for common command sequences. Together, these features provide a display-facility that considerably augments INTERLISPs otherwise quite sophisticated user interface. Although programs are written in a programming language, the human process of programming often occurs within a programming environment-a set of software tools that assist in different aspects of the programming process [1]. A major feature of the INTERLISP [2] environment is a structure-oriented editor whose commands operate on structural objects (e.g., atoms, S-expressions) rather than on textual objects (e.g., characters, lines). These commands deal with and modify in-core S-expressions rather than external textual representations INTERLISP's editor has evolved into a highly sophisticated tool. It's sophistication, however, is marred by one major drawback: it is built around a teletype-style interaction. If you wish a visual presentation of the expression being edited, you must explicitly request that it be typed out on the terminal. While this made sense when INTERLISP was originally developed (the late 1960's when display terminals were rare), it is now a hindrance, since display technologies can add considerable power and comfort to a human interface. A display-oriented editor (called DEI)) has been built to bring some of this power and comfort to the INTERLISP environment. DED includes the following features: • The display screen is divided into two regions: one is for the standard style of interaction with INTERLISP's editor; the other gives a prettyprinted version of the expression being edited. • The prettyprinter allows ellision: the most detailed parts of the prettyprinted expression are shown in abbreviated form. • The user may zoom in or out to see the expression with more or less detail. • There are several "arrow" keys which can be used to move the "cursor" on the prettyprinted expression (in addition to INTERLISP's …