John E. Howland

Teaching computer science principles to liberal arts students using Scheme

The Scheme dialect of Lisp is being used as an expository notation in introductory courses for liberal arts students at Trinity University. Terminology from natural language identifying parts of speech, such as verb, noun, pronoun and adverb, is used to present Scheme syntax and semantics to non programmers. Simple working models of various computer science topics are described. Experiences from two Trinity computer science courses are presented.

APL as a lingua franca in the computer science curriculum

In the last decade computer science has been struggling to establish its independent identity, pressured on one side by those who refuse to admit the existence of any new sciences and on the other by those who see computer science as no more than the art of constructing computer programs. We who are teaching computer science are caught in the middle. We must teach our students some of the art of computer technology through programming courses, but we also must instill in them those principles of the science of computing which set it apart as a discipline in its own right. We must keep ourselves from spending all our time teaching our students to program in a variety of different languages so they can get jobs as technologists. But we must also beware of spending an inordinate amount of time on the theory without teaching programming basics.

Typesetting APL using a Macintosh

This paper describes a low-cost approach to providing high quality printing of text which contains APL characters as well as other text fonts. APL fonts for the Macintosh#8482;computer and the Apple LaserWriter#8482;printer have been developed which allow low-cost typesetting of APL expressions and functions. Since the Macintosh computer can be used as a work station on several commercial typesetting machines, these fonts can be used to provide commercial quality printing of APL manuscripts.

Using J as expository language in the teaching of computer science to liberal arts students

APL and J are seldom, if ever, used in the teaching of college or university courses. Recently, the author has developed a new laboratory based computer science course for liberal arts students in which students are introduced to 13 core computer science topics. Programming language is used in an expository fashion to describe each topic by building simple working models of each topic. These models are then used as the basis of laboratory experiments in a co-requisite laboratory course. Students are not taught programming in this course, but rather, are taught just enough of the syntax and semantics of the language to be able to read and understand the exposition and models. Initially, Scheme was used in the lecture notes and laboratory materials developed for this course. Recently, however, an experiment is under way to replace the use of Scheme in this course by J. The development of this course and laboratory was funded by the Meadows Foundation and NSF grant DUE 9452050.

Design of a new user interface for APL

Much progress has been made in APL systems during the last 10 years, however, most implementations still use the standard del editor, systems commands and a character oriented, user-typed, command interface. Even the APL systems available for new graphics based workstation systems, such as Macintosh and Sun, do not fully exploit the user interface standards for those systems. It is now time to consider establishing a new standard user interface for APL running on hardware systems which support bit mapped graphics displays and a pointing device. This paper presents such a design which is based in part on the Macintosh user interface, but includes special features for handling the APL workspace environment.

Structured development of menu-driven application systems

Presenting the user of an application system with a menu of choices is a valuable approach to the human interface problem. In a complex system this may take the form of a tree of menus that is presented. This tree of menus can also be used as the basis for a top-down development of the application system. This paper describes a programming system which can be used to acquire the tree of menus and structure the development of a menu-driven application system in a top-down fashion. Objects called augmented menus contain not only the textual representation of the choices presented the user (in three forms), but also the action to be taken for each choice. A menu-manager program accesses the specified augmented menu, displays the choices and executes the selected action. This function eleminates much of the work of the application developer. This development system is illustrated with three applications: an information storage and retrieval system, a class-roll record-keeping system and a text-editing system.

APROL: a hybrid language

This paper describes the design of a hybrid language which combines the features of an array processing language and lisp dialect in a consistent and useful manner. This language, APROL (Array PROcessing Lisp) is derived from the J dialect of APL and the Scheme dialect of Lisp. The base syntactic structure is taken from Scheme, while the array processing features are based on the J programming language. A prototype implementation has been made and some experiences with this implementation are described. This implementation uses J as an imbedded array processing engine in a Scheme intrepreter/compiler.The language as specified provides a set of data types and manipulation tools which is more diverse than found in either Scheme or J. APROL allows the programmer to apply array processing functions to lists of arrays in the Scheme style and list processing functions to arrays of lists in typical J style. The result is a language which not only brings array processing capabilities to Scheme, but also significantly extends the functionality of the Scheme language.

A system for compiling fonts

An interactive system for specifying fonts using an object oriented approach, based on cubic splines, is given. An interactive Bezier curve editor is described as well as systems for compiling bit image fonts from their geometric descriptions and a system for compiling PostScript programs which can be used to render fonts on a PostScript printer or typesetter.

Scheme as an expository language for liberal arts students

The Scheme dialect of Lisp is being used as an expository notation in introductory courses for liberal arts students at Trinity University. Terminology from natural language identifying parts of speech, such as verb, noun, pronoun, adverb, etc., is used to present Scheme syntax and semantics to non programmers. Simple working models of various computer science topics are described. Experiences from two Trinity computer science courses are presented.

APL/Z80: An APL interpreter for Z80 microcomputers

An APL interpreter for Z80 microcomputers is described. APL/Z80 extends APL applications to the realm of low-cost personal computers. For example, APL/Z80 can be configured to run on Z80 systems with video console, 28K byte workspace, dual floppy disks for less than