Practical uses of a model of APL

• Authors: Kenneth E. Iverson;Arthur T. Whitney
• Venue: APL '82 Proceedings of the international conference on APL
• Year: 1982

This paper discusses the use of a general model of APL (written in APL) which allows convenient definition of new operators and functions and experimentation with their use. Use of the model is illustrated by a number of functions and operators, some of which have been previously discussed, and some (such as the operator til) which are new. Details of the model itself are not treated. The effective use of new facilities introduced into APL systems is often long delayed, not only because of a programmer's tendency to cling to familiar ways, but also because the abstract, formal treatment necessary to the specification of a new facility often makes its assimilation and use seem unduly difficult. Working models of new facilities available before their actual introduction can be very helpful in teaching their use, and very effective in speeding their widespread application. However, the development of an accurate model for each new facility can, especially in the case of new operators, be burdensome, and we have found that a general model of the APL interpreter, developed primarily for use by the language designers in the design and modelling of new extensions, can also be useful in providing specific models for the enlightenment of users. This paper discusses such uses of the general model, employing illustrations executed by the version available on the I.P. Sharp Associates APL system. Except for information necessary for understanding its use, details of the model will not be discussed here. The model incorporates a number of facilities proposed in earlier papers [1 2 3]; the more fundamental among them are illustrated below. The model, invoked by executing the function &Dgr;APL, accepts character input and parses and executes the expression entered. 0-origin indexing is used throughout the paper.