The next OUPS meetup will take place on Wednesday, 29th of April 2026. It will start at 6:30pm at the 45 rue d’Ulm in Paris. It will be in the in the Rataud amphitheater.
It’s not in Jussieu as usual but in ENS Ulm! If you’re not familiar with the place, there is a map of the buildings.
Please, register on meetup as soon as possible to let us know how many pizza we should order.
For more details, you may check the OUPS’ website .
Moreover, we’d like to announce that the organizing team moved to the OCaml Zulip. Feel free to contact us there if you’d like to suggest talks.
This time we’ll have the following talks:
When Turing machines meet GADTs – Florian Angeletti
Abstract
Have you ever wondered why one needs to write down explicit
unreachable clauses in a GADT-pattern matching? Or how much
computation one can sneak inside an OCaml type?
This talk proposes to answers those questions and more with a deep dive
into GADTs, the OCaml compiler implementation of the exhaustiveness
checking for pattern match, and how to best trick the typechecker into
finding the BB(3) champion by itself.
Extending OCaml’s pattern matching – Yanni Lefki
Abstract
Pattern matching has been studied for decades and has been the subject of extensive research and numerous extensions. Nevertheless, recent language features—such as Rust’s if-let construct, and recent work such as Cheng and Parreaux (OOPSLA 2024), suggest that there is still room for improvement. We propose a streamlined approach that unifies pattern matching with extended forms of conditionals.
In particular, our prototype introduces binding-boolean-expressions, which allow variables to be bound within pattern guards, within if-conditions (and subsequently used in the then branch), and within while-conditions (and used in the loop body). Our system also incorporates Haskell-style views, enabling the definition of smart deconstructors, the dual of smart constructors.
In this talk, we present an ML-like language equipped with evaluation rules, typing rules, and a simple compilation scheme. We conclude with a demonstration of our implementation: an OCaml PPX prototype that parses an extended ML syntax exposing these constructs, type-checks programs according to our (highly intuitive!) rules, and translates them into a correct OCaml AST via our (non-optimizing) transformation.
After the talks there will be some pizzas offered by the OCaml Software Foundation and later on we’ll move to a pub nearby as usual.