Design and implementation of a diagnostic compiler for PL/I

Abstract

PL/C is a compiler for a dialect for PL/I. The design objective was to provide a maximum degree of diagnostic assistance in a batch processing environment. For the most part this assistance is implicit and is provided automatically by the compiler. The most remarkable characteristic of PL/C is its perseverance—it completes translation of every program submitted and continues execution until a user-established error limit is reached. This requires that the compiler repair errors encountered during both translation and execution, and the design of PL/C is dominated by this consideration. PL/C also introduces several explicit user-controlled facilities for program testing. To accommodate these extensions to PL/I without abandoning compatibility with the IBM compiler, PL/C permits “pseudo comments”—constructions whose contents can optionally be considered either source text or comment. In spite of the diagnostic effort PL/C is a fast and efficient processor. It effectively demonstrates that compilers can provide better diagnostic assistance than is customarily offered, even when a sophisticated source language is employed, and that this assistance need not be prohibitively costly.