ICFP 2021
Sun 22 - Sat 28 August 2021

The Haskell Implementors’ Workshop is a forum for those involved in implementing Haskell systems, infrastructure, libraries and tools, for people generally involved in implementing Haskell technology. We share our work and discuss future directions and collaborations with others.

In 2021, the Haskell Implementors’ Workshop will be co-located with ICFP 2021.

The workshop does not have proceedings. Talks and/or demos are proposed by submitting an abstract and selected by a small program committee. The workshop will be informal and interactive, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks.


We are happy to announce that HIW 2021 features the following keynote.

Haskell reinterpreted – large-scale real-world experience with the Mu compiler in Financial Markets

Speaker: Bengt Marten Agren (Global Head of Modelling & Analytics Group, Financial Markets, Standard Chartered Bank)

Abstract: For over 11 years, Standard Chartered has maintained its own proprietary compiler for a dialect of Haskell called “Mu”. In this talk we present its origins in the context of a global Financial Markets business, a rationale for the main differences between Mu and Haskell (such as strictness by default), and choices on compiler and library design, such as whole-program compilation, and serialisation of any computation for parallel execution. We conclude with some code and language extension usage statistics from our production code repository, and present a plan to bridge the gap between Mu and Haskell in the near future.

Call for Talks

The 13th Haskell Implementors’ Workshop is to be held alongside ICFP 2021 this year virtually. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure, to share their work and discuss future directions and collaborations with others.

Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings. The workshop will be informal and interactive, with open spaces in the timetable and room for ad-hoc discussion, demos and lightning talks.

Scope and Target Audience

It is important to distinguish the Haskell Implementors’ Workshop from the Haskell Symposium which is also co-located with ICFP 2021. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors’ Workshop will have no proceedings – although we will aim to make talk videos, slides and presented data available with the consent of the speakers.

The Implementors’ Workshop is an ideal place to describe a Haskell extension, describe works-in-progress, demo a new Haskell-related tool, or even propose future lines of Haskell development. Members of the wider Haskell community encouraged to attend the workshop – we need your feedback to keep the Haskell ecosystem thriving. Students working with Haskell are specially encouraged to share their work.

The scope covers any of the following topics. There may be some topics that people feel we’ve missed, so by all means submit a proposal even if it doesn’t fit exactly into one of these buckets:

  • Compilation techniques
  • Language features and extensions
  • Type system implementation
  • Concurrency and parallelism: language design and implementation
  • Performance, optimization and benchmarking
  • Virtual machines and run-time systems
  • Libraries and tools for development or deployment


We invite proposals from potential speakers for talks and demonstrations. We are aiming for 20-minute talks with 5 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words.

Submissions can be made via HotCRP at https://icfp-hiw21.hotcrp.com/ until June 30th (anywhere on earth).

We will also have lightning talks session. These have been very well received in recent years, and we aim to increase the time available to them. Lightning talks be ~7mins and are scheduled on the day of the workshop. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators.


Due to the on-going COVID-19 situation, ICFP (and, consequently, HIW) will be held remotely this year. However, the organizers are still working hard to provide for a great workshop experience.

While we are sad that this year will lack the robust hallway track that is often the highlight of HIW, we believe that this remote workshop presents a unique opportunity to include more of the Haskell community in our discussion and explore new modes of communicating with our colleagues. We hope that you will join us in making this HIW as vibrant as any other.