Types and Semantics for Extensible Data Types (Extended Version)

TL;DR

This paper introduces a new type system and core calculus that natively supports initial algebra semantics, enabling flexible extension of data types and functions in programming languages.

Contribution

It provides a novel type discipline and core calculus for languages with native support for initial algebra semantics, improving extensibility and efficiency.

Findings

Developed a type discipline for initial algebra semantics

Designed a core calculus supporting native data type extensions

Demonstrated potential for more efficient code generation

Abstract

Developing and maintaining software commonly requires (1) adding new data type constructors to existing applications, but also (2) adding new functions that work on existing data. Most programming languages have native support for defining data types and functions in a way that supports either (1) or (2), but not both. This lack of native support makes it difficult to use and extend libraries. A theoretically well-studied solution is to define data types and functions using initial algebra semantics. While it is possible to encode this solution in existing programming languages, such encodings add syntactic and interpretive overhead, and commonly fail to take advantage of the map and fold fusion laws of initial algebras which compilers could exploit to generate more efficient code. A solution to these is to provide native support for initial algebra semantics. In this paper, we develop such a solution and present a type discipline and core calculus for a language with native support for initial algebra semantics.