Six Language Extensions to Enhance the Portability of Mathematical Software Written in PL/I: Background and Justification

摘要

This report proposes six extensions to ANS PL/I, which is being revised by the American National Standards Committee X3J1. The new features include environmental enquiry functions, generalization of restricted expressings (compile-time expressions), liberalization of the contexts of restricted expressions, a named-literal declaration type, explicit precision specification for constants, and a pragmatic statement for expressing conditions that an implementation must satisfy for acceptable compilation. Used together, these features will give numerical analysts access to properties of an implementation's floating-point arithmetic in exactly the ways required to ease the burden of tailoring a program's precision specifications to new environments. In many cases it will be possible to write PL/I programs that are completely self-adapting to their host environment. Effective definition of the environmental enquiry functions will require the incorporation of an explicitly parameterized model of floating-point arithmetic. If such a model is integrated into the Standard, numerical analysts will be able to state and prove theorems about their programs' error bounds by appealing directly to the Standard. (ERA citation 07:055915)