We have the pleasure of celebrating the birthdays of Camille Saint-Saëns and Karl Schwarzschild by announcing the release of OCaml version 5.4.0. Some of the highlights of OCaml 5.4.0 are: Labelled tuples It is now possible to put labels on tuple fields let ( * ) (x,~dx) (y,~dx:dy) = x*.y, ~dx:(x *. dy +. y *. dx ) Those labeled tuples are equivalent to SML records: they are an order-dependent and structurally-typed variants of records. They are mostly intended for local types. Array literal syntax support for immutable arrays and floatarrays The array literal syntax is now shared by array-like primitive datatypes, like 'a array, floatarray and immutable array iarray. For instance, this code let x = let x = Array.Flotarray.create 3 in Array.Flotarray.set x 0 1.; Array.Flotarray.set x 1 2.; Array.Flotarray.set x 2 3.; x can now be written let x : floatarray = [|0.; 1.; 2.|] This also supported in patterns let one = match x with | [|_;y;_|] -> Some y | _ -> None However array indexing still needs to go through user-defined indexing operator let (.$()) = Array.Floatarray.get let (.$()

Version 1.14 (2025-10-02) Nickel 1.14 has no core language changes. It adds position information to YAML documents, so that if some imported YAML breaks a contract then Nickel can blame the correct...

How CodeCommons uses SWH-fuse and the Kraken compressed graph to map open source: 8K files/sec and solving 10K process scaling.

Scientists, research institutions, funders, libraries and publishers must all improve software practices.

The Merlin team is excited to share that you can now try out an experimental branch of Merlin that leverages OCaml 5's domains and effects! This is Merlin-domains, and we'd love for you to test it and share your feedback. What is Merlin-domains? Merlin-domains is an experimental branch that uses domains and effects to implement two optimisations to improve performance in large buffers: partial typing and cancellation. As a reminder, Merlin is the editor service that powers OCaml's IDE features—if you're using the OCaml Platform extension with VS Code or ocaml-eglot with Emacs, you're already using Merlin under the hood through OCaml LSP Server. Why This Matters While Merlin has had relatively few performance complaints over the years, in some contexts like very large files, the parsing-typing-analysis mechanism could sometimes cause slowdowns. The experimental branch addresses this in a clever way. When you run an analysis command on a very large file, the type-checker will progress up to the location that makes the analysis possible, run the analysis phase, return the result, and then continue typing the file. This separation is made possible through control flow management enabled by effects, with two domains interacting with each other. The result? Analysis phases become much more efficient! This is a great example of migrating a regular OCaml application to take advantage of multicore. Learn More at Lambda World Want to understand the technical details? Sonja Heinze and Carine Morel will present their talk "When magic meets multicore - OCaml and its elegant era of parallelism" at Lambda World, where they'll dive into how this experimental branch works internally. How to Test It Currently, the branch is in its incubation phase. To test it, pin the branch in the switches where you want to experiment: opam pin add https://github.com/ocaml/merlin#merlin-domains Although this experimental branch passes the test suite, your feedback is very important to help collect potential bugs we may have missed. The team has added a Bug/Merlin-domains label to organize tickets related to this branch. What's Next The goal is for this branch to eventually become the main branch, so that all users can benefit from these improvements. The rest of the ecosystem depending on Merlin, including OCaml LSP Server, will be adapted to take full advantage of these new features. We need you! Try out merlin-domains with your real-world OCaml projects and share your experience on the Discuss thread. Your testing and feedback will help shape the future of Merlin!

The second part of a tutorial on how to quickly write a formatter for a programming language using Topiary, our open-source formatting engine based on Tree-sitter.

Distinguished Reviewer Awards This year, we had an exceptional Review Committee with over 100 RC members and 8 Associate Chairs. Nevertheless, several people in our group of AEs and chairs explicitly…

This two-day event celebrates the career and accomplishments of Olivier Danvy on the occasion of his 64th birthday. Olivier is a visionary in the field of programming languages and is well-known for…

A tiny fix, that tested on a closed-source codebase of over 16k modules took formatting inplace from ~10.5 minutes to ~19seconds. This fixes #1176

Common issues and best practices managing large dependency graphs

We sat down with Phil Wadler, one of the most influential folks in the Haskell community, functional programming, and programming languages, responsible for type classes, monads, and much more. We tak...

The Software Heritage Open Science Strategic Blueprint is a roadmap to make code a permanent part of the scientific record.

North American Hackathon The Haskell Foundation is proud to announce the inaugural AmeriHac, a two day haskell hackathon, with this iteration being in New York City! Jane Street has kindly offered to ...

The story of how I implemented qualified aliases in Liquid Haskell