Interactive Debugging for Extensible Languages in Multi-Stage Transformation Environments

Extensible languages have a base language that can be extended incrementally with new language extensions, forming a stack with high-level languages on top and lower level languages at the bottom. Programs written with these languages are usually a mixture of code using base language and several language extensions. These extensions come with generators that translate higher level language constructs to lower levels and ultimately to base language. Program bugs appearing at runtime can be introduced on the source level by language users or through faulty transformation rules by language engineers. The latter category of bugs are often analyzed with a base language debugger, because language constructs introducing the bug on intermediate levels usually have no representation on the source level. However, due to the semantic gap between generated code and the intermediate program where a bug is introduced, users have to map between abstraction levels manually, which is error prone and requires additional effort besides analyzing the bug. In this paper we present an approach to build multi-level debuggers for extensible languages that allow language users to debug their code on the source level and language engineers to debug on intermediate levels created during code generation. We illustrate this approach with an implementation for the MPS language workbench and mbeddr C, an extensible C language.