Abstract. Forwarding is a technique for providing default attribute definitions in attribute grammars that is helpful in the modular implementation of programming languages. It complements existing techniques such as default copy rules. This paper introduces forwarding, and shows how it is but a small extension of standard higher-order attribute grammars. The usual tools for manipulating higher-order attribute grammars, including the circularity check (which tests for cyclic dependencies between attribute values), carry over without modification. The closure test (which checks that each attribute has a defining equation) needs modification, however, because the resulting higher-order attribute grammars may contain spurious attributes that are never evaluated, and indeed that need not be defined. 1

Domain specific languages (DSLs) are increasingly used today. Coping with complex language definitions, evolving them in a structured way, and ensuring their error freeness are the main challenges of DSL design and implementation. The use of modular language definitions and composition operators are therefore inevitable in the independent development of language components. In this article, we discuss these arising issues by describing a framework for the compositional development of textual DSLs and their supporting tools. We use a redundance-free definition of a readable concrete syntax and a comprehensible abstract syntax as both representations significantly overlap in their structure. For enhancing the usability of the abstract syntax, we added concepts like associations and inheritance to a grammarbased definition in order to build up arbitrary graphs (as known from metamodeling). Two modularity concepts, grammar inheritance and embedding, are discussed. They permit compositional language definition and thus simplify the extension of languages based on already existing ones. We demonstrate that compositional engineering of new languages is a useful concept when project-individual DSLs with appropriate tool support are defined.

Programming languages and programming tasks are rarely a perfect fit: often a program could be much clarified by using a number of tailored language features...

The emergence of crosscutting concerns can be observed in various representations of software artifacts (e.g., source code, models, requirements, and language grammars). Although much of the focus of AOP has been on aspect languages that augment the descriptive power of general-purpose programming languages, there is also a need for domain-specific aspect languages that address particular crosscutting concerns found in software representations other than traditional source code. This paper discusses the issues involved in the design and implementation of domain-specific aspect languages that are focused within the domain of language specification. Specifically, the paper outlines the challenges and issues that we faced while designing two separate aspect languages that assist in modularizing crosscutting concerns in grammars. 1