A x Grammars for Programming LanguagesC

AAx Grammars are members of the family of Two-Level Grammars, along with W-grammars, Metamorphosis Grammars and Attribute Grammars. In this tutorial we shall be concerned with the nature and rationale of AAx Grammars and their application in describing programming languages. Some parsing and aax evaluation methods for deterministic and nondeterministic AAx Grammars are discussed. By means of an example, a comparison is made with W-grammars and Attribute Grammars. Informatics is full of artiicial languages, not only many programming languages, specii-cation languages and mathematical notations, but also the user interfaces of innumerable application systems. The greater part of informatics is paper work: the description and realization of the gments of the programmer's mind. The price of invention is description: what has been invented must be described, so that it can be communicated to others. All those artiicial languages need some description, be it informal or formal. The sixties of this century were an era of rapid development of algorithmic languages. The beginning and end of this period were marked by algol 60 23] and algol 68 30], respectively. Both languages were developed by a group of scientists as a lingua franca, to get away from the machine-oriented and vendor-oriented languages of the day. Both languages, by the formality of their description, set a new standard of precision. Both were accepted with mixed feelings 6], most readers nding their description far too complicated for ordinary programmers. The deenition of a programming language serves diierent (and rather contradictory) purposes: It serves as reference material for the more serious users of the language. To that end it has to have great expositionary and didactic value for human readers. A great language deenition is a literary work of art. It should enable specialists to answer questions about the language without having to take recourse to its compiler. To that end, it will have to describe the syntax and semantics of the language in a very precise way. Although it is possible to be very precise in unformalized prose, this will imply in general that the description has to be formal. Visiting the Technical University of Budapest on a tempus-grant.