Capturing Types

by Aleksander Boruch-Gruszecki, Martin Odersky, Edward Lee, Ondrej Lhotak, and Jonathan Immanuel Brachthäuser

In ACM Trans. Program. Lang. Syst. (TOPLAS). Association for Computing Machinery, 2023.

Abstract

Type systems usually characterize the shape of values but not their free variables. However, many desirable safety properties could be guaranteed if one knew the free variables captured by values. We describe CC, a calculus where such captured variables are succinctly represented in types, and show it can be used to safely implement effects and effect polymorphism via scoped capabilities. We discuss how the decision to track captured variables guides key aspects of the calculus, and show that CC admits simple and intuitive types for common data structures and their typical usage patterns. We demonstrate how these ideas can be used to guide the implementation of capture checking in a practical programming language.

Citation as BibTeX

@article{boruch2023capturing,
  author = {Boruch-Gruszecki, Aleksander and Odersky, Martin and Lee, Edward and Lhotak, Ondrej and Brachthäuser, Jonathan Immanuel},
  title = {Capturing Types},
  year = {2023},
  doi = {10.1145/3618003},
  publisher = {Association for Computing Machinery},
  address = {New York, NY, USA},
  journal = {ACM Trans. Program. Lang. Syst. (TOPLAS)}
}