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arXiv · 2507.16086

Understanding Haskell-style Overloading via Open Data and Open Functions

Andrew Marmaduke·Apoorv Ingle·J. Garrett Morris
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Abstract

We present a new, uniform semantics for Haskell-style overloading. We realize our approach in a new core language, System F$_\mathrm{D}$, whose metatheory we mechanize in the Lean4 interactive theorem prover. System F$_\mathrm{D}$ is distinguished by its open data types and open functions, each given by a collection of instances rather than by a single definition. We show that System F$_\mathrm{D}$ can encode advanced features of Haskell's of type class systems, more expressively than current semantics of these features, and without assuming additional type equality axioms.

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Andrew Marmaduke, Apoorv Ingle, J. Garrett Morris. 2025-07-21. Understanding Haskell-style Overloading via Open Data and Open Functions. https://arxiv.org/abs/2507.16086

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