June 23rd, 2024

Deriving Dependently-Typed OOP from First Principles

The paper delves into the expression problem in programming, comparing extensibility in functional and object-oriented paradigms. It introduces dependently-typed object-oriented programming, emphasizing duality and showcasing transformations. Additional appendices are included for OOPSLA 2024.

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Deriving Dependently-Typed OOP from First Principles

The paper discusses the expression problem in programming, highlighting the challenges of extending types with new producers and consumers simultaneously. It contrasts functional and object-oriented programs in terms of extensibility. The focus is on dependently-typed object-oriented programming, exploring it from first principles through duality. The authors derive a dependently typed calculus with dual language fragments, showcasing transformations like defunctionalization and refunctionalization. The paper emphasizes explaining dependently typed programming constructions as instances of duality. This extended version includes additional appendices not present in the published version, which will be part of the PACMPL issue for OOPSLA 2024. The work aims to fill a gap in the programming language landscape by systematically integrating dependent types into an object-oriented framework. The approach taken involves starting from a data-oriented language and deriving its dual fragment methodically. The implementation of this language and transformations serves to elucidate the relationship between functional and object-oriented paradigms in dependently typed programming.

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Link Icon 7 comments
By @abeppu - 4 months
Maybe I'm just missing something, but I'm not on board with the definitions they take in the introduction.

> the essence of object-oriented programming is programming against interfaces, which correspond to the type theoretic concept of codata and copattern matching

They then use the classic codata example of a Stream, with a head and a tail. The Stream they declare looks a lot more like the version of that concept in functional languages than the version of it in an OO one, but clearly it exists in both paradigms.

https://www.cs.cmu.edu/~15150/resources/libraries/stream.pdf https://hackage.haskell.org/package/Stream-0.4.7.2/docs/Data... https://docs.oracle.com/en/java/javase/21/docs/api/java.base...

By @msoad - 4 months
You can play around with the language itself here

https://polarity-lang.github.io/oopsla24/#ChurchEncodingCoda...

By @kikimora - 4 months
Very interesting. I’m on page 3 and already got a big AHA moment about OOP and FP duality.
By @_glass - 4 months
For me best described in, and also as a topic mentioned in the paper about the visitor pattern connection, "A Little Java, A Few Patterns". This book writes really impractical Java, but in such a Scheme way, that you really can understand the deep connections between functional and object-oriented programming.
By @peterbb_net - 4 months
Nice paper on an interesting topic. I’ve not had a chance to read the paper thoroughly, but the judgmental equality ended up weaker than I anticipated. I’d hope we’d end up with alpha-equivalent codefs being judgmentally equal.

Which makes me wonder what the next steps for a proof assistant based on this is. Will the de-/refunctionalization play an active role in the proof assistant as well, thus solving it as described in section 4.1?

By @grafs50 - 4 months
Interesting, I wondered what it would even mean to derive a programming paradigm.