Implementing type systems for the IDE with Xsemantics

• We present Xsemantics a DSL for implementing type systems and semantics for Xtext languages.
• We describe its features through examples.
• We describe features that target IDE.

Xsemantics is a DSL for writing type systems, reduction rules and, in general, relation rules for languages implemented in Xtext (Xtext is an Eclipse framework for rapidly building languages together with all the typical IDE tooling). Xsemantics aims at reducing the gap between the formalization of a language (i.e., type system and operational semantics) and the actual implementation in Xtext, since it uses a syntax that resembles the rules in a formal setting. In this paper we present the main features of Xsemantics for implementing type systems and reduction rules through examples (Featherweight Java and lambda calculus). We show how such implementations are close to the actual formalizations, and how Xsemantics can be a helpful tool when proving the type safety of a language. We also describe the new features of Xsemantics that help achieving a modular and efficient implementation of type systems. In particular, we focus on specific implementation techniques for implementing type systems that are suited for the IDE (in our context, Eclipse), in order to keep the tooling responsive and guarantee a good user experience.