Pathless Scala: a calculus for the rest of Scala

Recent work on the DOT calculus successfully put core aspects of Scala on a sound foundation, but subtyping in DOT is structural and therefore not easily amenable to studying the parts of Scala that are deeply tied to its nominal subtyping system. On the other hand, the Featherweight Java calculus has proven to be a great basis for studying many aspects of Java and Java-like languages. Continuing this tradition, we present Pathless Scala: an extension of Featherweight Generic Java that closely models multiple inheritance and intersection types as they exist in the Scala language today. We define the semantics of Pathless Scala by erasing it to a simpler calculus in a way that closely models how Scala is compiled to Java bytecode in practice. More than a one-off, we believe that this calculus could be extended to describe many more features of Scala, although reconciling it with DOT remains an open problem.