Bringing APL down to earth on the DECsystem-10: Standard characters and a standard editor

The APL programming language provides an unpre­ cedented combination of simplicity and power. Simplic­ ity characterizes program preparation. Since APL code is interpreted, programs ("functions," as they are called in APL) can be executed as soon as they are written, without the frustrating delays commonly interpolated by compilers. Furthermore, any APL program (function) can pass control to another APL program (function) without a preliminary time-consuming linking procedure. Finally, individual lines of APL code can be interpreted outside an official function definition, a feature that encourages trial-and-error learning. In all these respects, APL shares or improves upon the breezy informality of interactive BASIC, but, unlike BASIC, APL does not disappoint advanced students of programming. APL is a superior programming system for statistical data analysis. The interactive flexibility of APL facilitates exploratory data analysis. In addition, APL provides powerful operators for the manipulation and transforma­ tion of tabular (matrix) data structures. Formulas for univariate or multivariate analysis can be transcribed into APL on a line-to-line basis (i.e., one line of mathe­ matical formula converts to one line of APL code), instead of the one-line-to-many-line basis required by ALGOL, FORTRAN, or PASCAL-type languages. This one-to-one correspondence between mathematics and APL is hardly surprising, since APL was originally created not as a computer programming language, but as an improved notation for algebraic formula (Iverson, 1962).