Debugging with domain-specific events via macros

Abstract

Extensible languages enable the convenient construction of many kinds of domain-specific languages (DSLs) by mapping domain-specific surface syntax into the host language's core forms in a layered and composable way. The host language's debugger, however, reports evaluation and data details in ways that reflect the host language, instead of the DSL in its own terms, and closing the gap may require more than correlating host evaluation steps to the original DSL source. In this paper, we describe an approach to DSL construction with macros that pairs the mapping of DSL terms to host terms with a mapping to convert primitive events back to domain-specific concepts. Domain-specific events are then suitable for presenting to a user or wiring into a domain-specific visualization. We present a core model of evaluation and events, and we present a language design---analogous to pattern-based notations for macros, but in the other direction---for describing how events in a DSL's expansion are mapped to events at the DSL's level.