Generation of formatters for context-free languages

Abstract

Good documentation is important for the production of reusable and maintainable software. For the production of accurate documentation it is necessary that the original program text is not copied manually to obtain a typeset version. Apart from being tedious, this will invariably introduce errors. The production of tools that support the production of legible and accurate documentation is a software engineering challenge in itself. We present an algebraic approach to the generation of tools that produce typographically effective presentations of computer programs. A specification of a formatter is generated from the context-free grammar of a (programming) language. These generated formatters translate abstract syntax trees of programs into box expressions. Box expressions are translated by language-independent interpreters of the box language into ASCII or TEX. The formatting rules that are generated can easily be tuned in order to get the desired formatting of programs. We demonstrate this by means of real-life applications. Furthermore, we give a practical solution for the problem of formatting comments, which occur in the original text. The formatter generation approach proposed in this article can be used to generate formatting programs for arbitrary programming environments. Our formatter generation approach can be used to automatically generate formatters that have to be programmed explicitly in other systems.