SugarJ: library-based language extensibility

In the modern era of embedded domain-specific languages (DSLs) and language-oriented programming, two core requirements arise: Languages have to be ex-tensible and language extensions need to compose easily. Without language ex-tensibility, programmers are bound to a single (typically general-purpose) pro-gramming language and cannot benefit from all aspects of DSLs (for instance, domain-specific syntax or IDE support). Since software projects typically touch upon many domains, it is furthermore essential to support the composition of DSL embeddings for the common case of conflict-free language composition. For example, it should be possible to extend Java with SQL, XML or regular expres-sions with regard to their concrete syntax, IDE support (e.g., code completion), static analyses (e.g., XML Schema validation), and so forth. It should be simple for programmers to use any combination of such language extensions within a single source file. To address these goals, we propose to organize and implement language ex-tensions as libraries in the object language itself. In contrast to conventiona