Software Engineering and Programming Languages

A set of subroutines to allow algebraic manipulations on the IBM 7094 computer has been written using a List Processor, SLIP. A series of four problems of increasing difficulty were solved using these routines.

A method for storing strings is described which uses blocks of indefinite size, and is therefore completely dynamic. Its relation to similar schemes is discussed.

A routine has been developed which computes and prints out the symbolic derivative of an absolutely continuous elementary function of one or several variables. No use is made of list processing languages. The chain rule is applied and the result is edited to produce results as elegant and efficient as those obtained by hand computation. A subset may be imbedded in a formula translator to introduce a differentiation operator into an “algebraic” programming language.

The use and implementation of two new FORTRAN format conversions are discussed. These format types give the FORTRAN programmer control of input/output specifications at execution time.

An ALGOL compiler has been written by the ALCOR group for the IBM 7090. Some little known but significant techniques in compiler writing, together with organizational details of this compiler, are described. Timing estimates and an indication of compiler requirements are also given.

This note describes some FORTRAN subroutines to facilitate handling of tape files. They allow symbolic naming or information files, without violating the casual scientific programmer's idea of simplicity. Some comments on two years use of these subroutines are given.

A three-pass compiler with the following properties is briefly described: The last two passes scan an intermediate language produced by the preceding pass in essentially the reverse of the order in which it was generated, so that the first pass is the only one which has to read the relatively bulky problem-oriented input. The double scan, one in either direction, performed by the first two passes, allows the compiler to remove locally constant expressions and recursively calculable expressions from loops and to do the important part of common subexpression recognition. Optimization such as the effective use of index registers, although as important, is not discussed since the object code which would be most efficient is highly machine dependent. The discussion is in terms of a FORTRAN-like language, although the technique is applicable to most algebraic languages.