Subset/G PL/I and the PL/I Standard

Abstract

Subset/G PL/I (G for General Purpose) is a subset of full Standard PL/I. Both Subset/G PL/I and Standard PL/I are defined by standards issued by the American National Standards Institute. Subset/G evolved in the late 1970's as a result of a growing realization that full PL/I was a remarkably effective (if much maligned) language but at the same time a difficult language to implement and to teach. Subset/G was designed so as to preserve the most useful properties of PL/I while deleting features that were either little used, uneconomic to implement, or inappropriate to what we now know about good programming practice. Full Standard PL/I is a descendant of the F-level PL/I language originally developed by IBM in the early 1960's. One of the design objectives of the original language was that it should be applicable to scientific programming, commercial programming, and systems programming. Part of the original rationale for this objective was that PL/I was intended to replace Fortran, Cobol, and assembly language. But there was also another reason: the growing number of applications that spanned more than one category. Subset/G also has this design objective, although some other design objectives of early PL/I were dropped, notably the principle that any construct that could reasonably be given a meaning should be acceptable. That rationale remains a major reason why Subset/G is a significant and useful language despite the many other languages that have emerged since PL/I was first designed.