Inferring Scope through Syntactic Sugar

Justin Pombrio (Brown University, USA) gives the third talk in the fifth panel, Inference and Analysis on the 3rd day of the ICFP conference. Co-written by Shriram Krishnamurthi (Brown University, USA) and Mitchell Wand (Northeastern University, USA). Many languages use syntactic sugar to define parts of their surface language in terms of a smaller core. Thus some properties of the surface language, like its scoping rules, are not immediately evident. Nevertheless, IDEs, refactorers, and other tools that traffic in source code depend on these rules to present information to users and to soundly perform their operations. In this paper, we show how to lift scoping rules defined on a core language to rules on the surface, a process of scope inference. In the process we introduce a new representation of binding structure--scope as a preorder--and present a theoretical advance: proving that a desugaring system preserves alpha-equivalence even though scoping rules have been provided only for the core language. We have also implemented the system presented in this paper.