Generic Programming with Extensible Data Types; Or, Making Ad Hoc Extensible Data Types Less Ad Hoc

TL;DR

This paper introduces a new approach to generic programming with extensible data types using row types, formalized in System Rω, enabling flexible and modular data structure manipulation.

Contribution

It extends row typing to support generic programming over rows, capturing complex patterns like lifting and duality without field-specific constraints.

Findings

Formalization in System Rω with row types

Denotational semantics provided in Agda

Supports flexible, modular data type operations

Abstract

We present a novel approach to generic programming over extensible data types. Row types capture the structure of records and variants, and can be used to express record and variant subtyping, record extension, and modular composition of case branches. We extend row typing to capture generic programming over rows themselves, capturing patterns including lifting operations to records and variations from their component types, and the duality between cases blocks over variants and records of labeled functions, without placing specific requirements on the fields or constructors present in the records and variants. We formalize our approach in System R{\omega}, an extension of F{\omega} with row types, and give a denotational semantics for (stratified) R{\omega} in Agda.