A technique is presented for global analysis of program structure in order to perform compile time optimization of object code generated for expressions. The global expression optimization presented includes constant propagation, common subexpression elimination, elimination of redundant register load operations, and live expression analysis. A general purpose program flow analysis algorithm is developed which depends upon the existence of an "optimizing function." The algorithm is defined formally using a directed graph model of program flow structure, and is shown to be correct. Several optimizing functions are defined which, when used in conjunction with the flow analysis algorithm, provide the various forms of code optimization. The flow analysis algorithm is sufficiently general that additional functions can easily be defined for other forms of global code optimization.

A common approach to the teaching of Programming Languages (course 12, Curriculum 68) has been to teach several languages, each demonstrating-a feature deemed significant, such as ALGOL, LISP, SNOBOL, and COBOL [3,7]. The problem that exists with this method is that far too much time is spent learning the details necessary to use the languages, leaving time for only a few trivial programs in each language. A popular alternative to this approach is to teach the course using a single general-purpose language which has a broad repertoire of language features, such as PL/I. While this method successfully avoids much of the detail which characterizes the former, it too seems to have a serious drawback. The student can become quite talented at programming in the language and still have very little feel for the implications of the higher level language structur~ at the machine level. Moreover, these languages 'typically provide no means by which the student can readily investigate these implications. Hence, ALGOL-E is proposed as a programming language system which provides such a capability.

One of the difficulties faced in implementing information management and retrieval systems is that each case seems to present its own special complexities. As a result information retrieval systems typically fall behind their programming schedule and have many bugs when delivered. In this paper a set of basic operations on types of files are defined. These operations are intended to fulfill the same role for information retrieval systems programmers that functions such as LOG(X) fill for mathematical applications programmers.. they should make the job very much easier. The file operations have been implemented as a run-time package written in FORTRAN IV and Burroughs Extended Algol. The approach has been used to develop three different information management systems; an APL interactive computing system, a generalized information retrieval system, and a specialized information retrieval system for map oriented data. These systems are described.