Meta-Language Support for Type-Safe Access to External Resources

Meta-programming applications often require access to heterogeneous sources of information, often from different technological spaces (grammars, models, ontologies, databases), that have specialized ways of defining their respective data schemas. Without direct language support, obtaining typed access to this external, potentially changing, information is a tedious and error-prone engineering task. The Rascal meta-programming language aims to support the import and manipulation of all of these kinds of data in a type-safe manner. The goal is to lower the engineering effort to build new meta programs that combine information about software in unforeseen ways. In this paper we describe built-in language support, so called \textit{resources}, for incorporating external sources of data and their corresponding data-types while maintaining type safety. We demonstrate the applicability of Rascal resources by example, showing resources for RSF files, CSV files, JDBC-accessible SQL databases, and SDF2 grammars. For RSF and CSV files this requires a type inference step, allowing the data in the files to be loaded in a type-safe manner without requiring the type to be declared in advance. For SQL and SDF2 a direct translation from their respective schema languages into Rascal is instead constructed, providing a faithful translation of the declared types or sorts into equivalent types in the Rascal type system. An overview of related work and a discussion conclude the paper.