Anthony Hassitt

Implementation of a high level language machine

Computing machines which directly execute the statements of a high level language have been proposed in the past. This report describes the actual implementation of such a machine: it is a computer whose “machine language” is APL. The machine is fully operational and correctly executes almost all of the APL operations on scalars, vectors, and arrays. The machine automatically allocates memory, executes statements, calls functions, converts numbers from one type to another, checks subscripts, and automatically detects many types of programmer errors.

Efficient evaluation of array subscripts of arrays

The APL language allows subscripted expressions such as A[I;J;K], where A is an array and I, J and K may be scalars, vectors or arrays of any size and shape. We describe an efficient method of evaluating these expressions. The method is quite general and yet it does recognize all the special cases in which multiple subscripts can be reduced to a simpler form. We show how the same mechanism can be used to evaluate other selection operations, such as transpose, and how selection operations may be combined.

An APL emulator on system/370

Emulation of an APL machine on a System/370 is exemplified by the APL Assist, a microprogram that enables APL. expressions and defined functions to be executed at the hardware level. This paper discusses what the APL Assist does, how it works, and the way it interacts with System/370 software. Execution times for APL programs with and without the Assist are compared.