Mon 5 - Sat 10 December 2022 Auckland, New Zealand

In modular programming, the famous Expression Problem describes the dilemma of modular extension for both datatypes and their operations in object-oriented and functional programming. Recently, Parreaux et al. propose a novel language called MLscript which features classes and traits, instance matching, union and intersection types, and principal type inference. In this abstract, we show that a small extension to MLscript gives a simple solution to the Expression Problem through precisely typed open recursion.