Meta-AspectJ (MAJ) is a language for generating AspectJ programs using code templates. MAJ itself is an extension of Java, so users can interleave arbitrary Java code with AspectJ code templates. MAJ is a structured metaprogramming tool: a well-typed generator implies a syntactically correct generated program. MAJ promotes a methodology that combines aspect-oriented and generative programming. A valuable application is in implementing small domain-specific language extensions as generators using unobtrusive annotations for syntax extension and AspectJ as a back-end. The advantages of this approach are twofold. First, the generator integrates into an existing software application much as a regular API or library, instead of as a language extension. Second, a mature language implementation is easy to achieve with little effort since AspectJ takes care of the low-level issues of interfacing with the base Java language. In addition to its practical value, MAJ offers valuable insights to metaprogramming tool designers. It is a mature metaprogramming tool for AspectJ (and, by extension, Java): a lot of emphasis has been placed on context-sensitive parsing and error reporting. As a result, MAJ minimizes the number of metaprogramming (quote/unquote) operators and uses type inference to reduce the need to remember type names for syntactic entities.

Program generation is among the most promising techniques in the effort to increase the automation of programming tasks. In this paper, we discuss the potential impact and research value of program generation, we give examples of our research in the area, and we outline a future work direction that we consider most interesting. Specifically, we first discuss why program generators have significant applied potential. At the same time we argue that, as a research topic, meta-programming tools (i.e., language tools for writing program generators) may be of greater value. We then illustrate our views on generators and meta-programming tools with our latest work on the Meta-AspectJ meta-programming language and the GOTECH generator. Finally, we examine the problem of statically determining the safety of a generator and present its intricacies. We limit our focus to one particular kind of guarantee for generated code---ensuring that the generated program is free of compile-time errors. We believe that this research direction will see significant attention and will make a difference in the mainstream adoption of meta-programming technology.