VALGOL II(ID:3260/val006)Val Schorre 1963 for Val's Algol Significant subset of Algol 60, part of META project Related languages
References: Extract: Introduction META II is not intended as a standard language which everyone will use to write compilers. Rather, it is an example of a simple working language which can give one a good start in designing a compiler-writing compiler suited to his own needs. Indeed, the META II compiler is written in its own language, thus lending itself to modification. Extract: History History The basic ideas behind META II were described in a series of three papers by Schmidt, Metcalf, and Schorre. These papers were presented at the 1963 National A.C.M. Convention in Denver, and represented the activity of the Working Group on Syntax-Directed Compilers of the Los Angeles SIGPLAN. The methods used by that group are similar to those of Glennie and Conway, but differ in one important respect. Both of these researchers expressed syntax in the form of diagrams, which they subsequently coded for use on a computer. In the case of META II, the syntax is input to the cemputer in a notation resembling Backus normal fore. The method of syntax analysis discussed in this paper is entirely different frem the one used by Irons and Bastian. All of these methods can be traced back to the mathematical study of natural languages, as described by Chomsky. Extract: How the META II Compiler Was Written How the META II Compiler Was Written Now we come to the most interesting part of this project, and consider how the META II compiler was written in its own language. [...] The META II compiler, which is an interpretive program for the META II machine, takes the syntax equations given in figure 5 and produces an assembly language version of this same interpretive program. Of course, to get this started, I had to write the first compiler-writing compiler by hand. After the program was running it could produce the same program as written by hand. Someone always asks if the compiler really produced exactly the program I had written by hand and I have to say that it was "almost" the same program. I followed the syntax equations and tried to write Just what the compiler was going to produce. Unfortunately I forgot one of the redundant instructions, so the results were not quite the same. Of course, when the first machine-produced compiler compiled itself the second time3 it reproduced itself exactly. The compiler originally written by hand was for a language called METAI. This was used to implement the improved compiler for META II. Sometimes, when I wanted to change the metalanguage, I could not describe the new metalanguage directly in the current metalanguage. Then an intermediate language was created -- one which could be described in the current language and in which the new language could be described . I thought that it might sometimes be necessary to modify the assembly language output, but it seems that it is always possible to avoid this with the intermediate language. [...] All subroutines in META II programs are recursive. When the program enters a subroutine a stack is pushed down by three cells. One cell is for the exit address and the other two are for labels which may be generated during the execution of the subroutine. There is a switch which may be set or reset by the instructions which refer to the input string, and this is the switch referred to by the conditional branch commands. The first thing in any META II machine program is the address of the first instruction. During the initialization for the interpreter, this address is placed into the instruction counter. Extract: Further Development of META Languages Further Development of META Languages As mentioned earlier, META II is not presented as a standard language, but as a point of departure frum which a user may develop his own META language. The term "META Language," with "META" in capital letters, is used to denote any compiler-writing language so developed. The language which Schmidt implemented on the PDP-1 was based on META I. He has now implemented an improved version of this language for a Beckman machine. Rutman has implemented LOGIK, a compiler for bit-time simulation, on the 7090. He uses a META language to compile Boolean expressions into efficient machine code. Schneider and Johnson have implemented META 3 on the IBM 7094, with the goal of producing an ALGOL compiler which generates efficient machine code. They are planning a META language which will be suitable for any block structured language. To this compiler-writing language they give the name META 4 (pronounced metaphor). Extract: META 4 Schneider and Johnson have implemented META 3 on the IBM 7094, with the goal of producing an ALGOL compiler which generates efficient machine code. They are planning a META language which will be suitable for any block structured language. To this compiler-writing language they give the name META 4 (pronounced metaphor). in Proceedings of the 19th ACM national conference January 1964 view details in ACM Computing Reviews 6(01) January-February 1965 view details in Computers & Automation 21(6B), 30 Aug 1972 view details The exact number of all the programming languages still in use, and those which are no longer used, is unknown. Zemanek calls the abundance of programming languages and their many dialects a "language Babel". When a new programming language is developed, only its name is known at first and it takes a while before publications about it appear. For some languages, the only relevant literature stays inside the individual companies; some are reported on in papers and magazines; and only a few, such as ALGOL, BASIC, COBOL, FORTRAN, and PL/1, become known to a wider public through various text- and handbooks. The situation surrounding the application of these languages in many computer centers is a similar one. There are differing opinions on the concept "programming languages". What is called a programming language by some may be termed a program, a processor, or a generator by others. Since there are no sharp borderlines in the field of programming languages, works were considered here which deal with machine languages, assemblers, autocoders, syntax and compilers, processors and generators, as well as with general higher programming languages. The bibliography contains some 2,700 titles of books, magazines and essays for around 300 programming languages. However, as shown by the "Overview of Existing Programming Languages", there are more than 300 such languages. The "Overview" lists a total of 676 programming languages, but this is certainly incomplete. One author ' has already announced the "next 700 programming languages"; it is to be hoped the many users may be spared such a great variety for reasons of compatibility. The graphic representations (illustrations 1 & 2) show the development and proportion of the most widely-used programming languages, as measured by the number of publications listed here and by the number of computer manufacturers and software firms who have implemented the language in question. The illustrations show FORTRAN to be in the lead at the present time. PL/1 is advancing rapidly, although PL/1 compilers are not yet seen very often outside of IBM. Some experts believe PL/1 will replace even the widely-used languages such as FORTRAN, COBOL, and ALGOL.4) If this does occur, it will surely take some time - as shown by the chronological diagram (illustration 2) . It would be desirable from the user's point of view to reduce this language confusion down to the most advantageous languages. Those languages still maintained should incorporate the special facets and advantages of the otherwise superfluous languages. Obviously such demands are not in the interests of computer production firms, especially when one considers that a FORTRAN program can be executed on nearly all third-generation computers. The titles in this bibliography are organized alphabetically according to programming language, and within a language chronologically and again alphabetically within a given year. Preceding the first programming language in the alphabet, literature is listed on several languages, as are general papers on programming languages and on the theory of formal languages (AAA). As far as possible, the most of titles are based on autopsy. However, the bibliographical description of sone titles will not satisfy bibliography-documentation demands, since they are based on inaccurate information in various sources. Translation titles whose original titles could not be found through bibliographical research were not included. ' In view of the fact that nany libraries do not have the quoted papers, all magazine essays should have been listed with the volume, the year, issue number and the complete number of pages (e.g. pp. 721-783), so that interlibrary loans could take place with fast reader service. Unfortunately, these data were not always found. It is hoped that this bibliography will help the electronic data processing expert, and those who wish to select the appropriate programming language from the many available, to find a way through the language Babel. We wish to offer special thanks to Mr. Klaus G. Saur and the staff of Verlag Dokumentation for their publishing work. Graz / Austria, May, 1973 in Computers & Automation 21(6B), 30 Aug 1972 view details |