June 2026 - Haskell-Cafe

bug in ghci module loading post 9.12.4?
by Evan Laforge 04 Jul '26

04 Jul '26

I recently upgraded from ghc 9.2 to 9.6 (I know, I'm slow), and one of the things I was looking forward to was better recompilation avoidance, that wouldn't be fooled by spurious mtime changes that are common with with e.g. git branch switches. Unfortunately, it seems to have gotten buggy at the same time! I upgraded again to 9.12.4 and it looks like it's still buggy. Either that or I'm doing things wrong somehow. Here's a repro, it requires 3 modules: % cat >BugA.hs module BugA where x :: Int x = 13 % cat >BugB.hs module BugB where import qualified BugA f :: IO () f = print BugA.x % cat >BugC.hs module BugC where import qualified BugB bug :: IO () bug = BugB.f % ghci -fobject-code # compile so we can load .o GHCi, version 9.12.4: https://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /Users/elaforge/qlib/dotfiles/.ghci Prelude> :load BugC [1 of 3] Compiling BugA ( BugA.hs, BugA.o ) [2 of 3] Compiling BugB ( BugB.hs, BugB.o ) [3 of 3] Compiling BugC ( BugC.hs, BugC.o ) Ok, three modules loaded. Leaving GHCi. % ghci Prelude> :load BugC Ok, three modules loaded. Prelude BugC> bug 13 As expected! Now go edit BugA.hs, and change 13 to say 14, and save. Now reload: Prelude BugC> :r [1 of 3] Compiling BugA ( BugA.hs, interpreted ) [Source file changed] Ok, three modules reloaded. Prelude BugC> bug 13 So that's not right! This will also cause linking errors if something was removed, though it's easier to reproduce the stale values. For my interpretation of what's going on, I believe previously it would have also reloaded BugB. While it has noticed that BugA must be reloaded (and switched to bytecode), it hasn't noticed that BugB is in the dependency path and should also be reloaded, and possibly winds up using stale values inlined into BugB.o. Is it a bug?

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monomorphism restriction vs unused
by Evan Laforge 23 Jun '26

23 Jun '26

I have a little DSL I use from ghci and I finally tracked down a minor annoyance, which is when I comment out some lines in a definition, sometimes certain now-unused `where` definitions now become ambiguity errors. Here's a minimized repro: ``` {-# LANGUAGE OverloadedStrings #-} -- {-# LANGUAGE NoMonomorphismRestriction #-} import Data.String (IsString(..)) data Thing a = Thing -- 1. IsString instance on concrete type. instance IsString (Thing ()) where fromString _ = Thing -- 2. trans is polymorphic trans :: Thing a -> Thing a trans = id -- 3. ambig is a simple binding under the Monomorphism Restriction, and is -- unused. ex :: () ex = () where unused = trans "k" -- Ambiguous type variable 'a0' ``` In place of `ex` imagine a large expression with many things in `where`, and part of the expression was temporarily commented out which just happened to contain the uses of `unused`. As the comment implies, this is ultimately a monomorphism restriction thing. My understanding is that `trans` keeps defaulting from happening and the restriction then forbids leaving `unused` polymorphic. It was confusing to me given that unused is unused, but I'm guessing the type checking runs before dead code elimination. So I think this is all working as intended, or rather, an unexpected interaction between defaulting being a "best effort" heuristic, and monomorphism restriction doing its thing, and the type checking -> dead code order, but all 3 things exist for good reasons which are unlikely to change. The way around is to turn on NoMonomorphismRestriction, which unfortunately counts as a flag change and hence causes ghci to not be able to load .o files... or compile the .o files with that too, but that of course may lead to unexpected redundant evaluation. https://www.haskell.org/onlinereport/decls.html#sect4.5.5 talks about "no way to enforce monomorphic use of an exported binding", but is this still relevant when it's usual to require type signatures for all top-level bindings? Are there still non-toplevel let/where-bound things which could result in redundant work?

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Haskell IDE
by Andrew Goh 19 Jun '26

19 Jun '26

Hi Haskell Cafe, Is anyone thinking of building a new functioning Haskell IDE based on GHC and GHCi. I am using a legacy Haskell plug-in for Eclipse IDE and the Haskell extension on VS Code, Miss Leksah much, and I simply wish that somebody will bring it back or develop a new IDE or a plug-in for the Eclipse IDE and maybe VS too. Warm Wishes, - Andrew

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ICFP 2026 Tutorials: Proposal Deadline on June 21!
by ICFP Publicity 18 Jun '26

18 Jun '26

ICFP 2026: Last Call for Tutorials *** Deadline: June 21, AoE ****Submission Portal*: https://icfp26events.hotcrp.com/ The 31st ACM SIGPLAN International Conference on Functional Programming (ICFP) is calling for tutorials! ICFP will be held in Indianapolis, IN, United States from *Monday, August 24 to Saturday, August 29, 2026*. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementation, principles, and uses of functional programming. *Tutorials* (or panels, discussions, etc.) should last approximately 3 hours each, and will be presented during ICFP and its co-located workshops and other events. Tutorials may focus either on a concrete technology or on a theoretical or mathematical tool. Tutorials may be intended primarily for researchers or for practitioners. Ideally, tutorials will have a concrete result, such as “Learn to do X with Y” rather than “Learn language Y”. The workshops, tutorials, etc. may occur on August 24th (the day before ICFP) and August 28-29th (the two days after ICFP). *All co-located events* must submit a proposal — workshops, tutorials, symposiums, or side meetings. Submission Details <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#submission-details> - Deadline for Tutorial Proposal Submission: June 21, 2026 - Notification of Acceptance: June 28, 2026 Prospective organizers of tutorials, panels, or discussions should submit proposals by the Tutorial deadline. Proposals should outline the objectives, intended audience, and planned activities. See the Submission Portal for details. *Submission Portal*: https://icfp26events.hotcrp.com/Selection Committee <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#selection-committ…> Event proposals will be evaluated by a committee comprising members from the ICFP 2026 organizing committee, in collaboration with the SIGPLAN executive committee. Contact Information <https://icfp26.sigplan.org/track/icfp-2026-icfp-tutorials#contact-informati…> For inquiries, please contact: Ben Greenman: blg(a)cs.utah.edu Jiasi Shen: sjs(a)cse.ust.hk We look forward to your proposals and to creating a vibrant and engaging program at ICFP 2026!

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call for talks, tutorials, performances: LeFUNK 2026 Leipzig (Germany) September 29/30
by Johannes Waldmann 16 Jun '26

16 Jun '26

LeFUNK 2026 Leipzig Workshop on Functional Programming September 29/30, Leipzig, Germany https://www.imn.htwk-leipzig.de/LFUNK2026/ abstract submission: by July 12 bringing together functional programming developers, researchers, enthusiasts and beginners to listen to talks, take part in tutorials, and join in interesting conversations; continuing the tradition of "Haskell in Leipzig" (started in 2006) Topics: in general: functional programming in applications, teaching, research. in particular: we welcome contributions in these areas expressive types interactive programming and proving functional programming for music and arts a contribution can be: a talk (30 min), a tutorial (90 min), a performance. Program Committee (under construction) Joachim Breitner, Lean FRO Andres Löh, Well Typed Henning Thielemann Johannes Waldmann, HTWK Leipzig Best regards, and see you - Johannes. NB: in order to add some actual Haskell content, here's a puzzle: explain the difference in numbers of test cases: ghci> import Test.LeanCheck ghci> check $ \ x y -> x || y == y || x +++ OK, passed 2 tests (exhausted). ghci> check $ \ x y -> (x || y) == (y || x) +++ OK, passed 4 tests (exhausted). you're welcome to bring puzzles to the workshop as well!

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POPL 2027 Call for Workshops
by Ningning Xie 11 Jun '26

11 Jun '26

POPL 2027 Call for Workshops Sun 10 - Sat 16 January 2027 Mexico City, Mexico https://popl27.sigplan.org/ ============================= Submission details Deadline for submission: 24 July 2026 Notification of acceptance: 4 August 2026 A workshop proposal should provide the following information: - Name of the workshop. - A short description (150-200 words) of the workshop. - Call for submissions. - Duration of the workshop. - Whether the workshop will be Conference-approved or SIGPLAN-approved (see below). - Organizers: names, affiliation, contact information, brief (100 words) biography. - Event format: workshop; type of submissions if any; review process; results dissemination. - Expected attendance and target audience. - Potential PC members - please do not contact them before the workshop is approved. - History of the workshop. - Plans for remote participation. Please submit your proposals at https://popl27.sigplan.org/track/POPL-2027-workshops-and-co-located-events --------------------------------------------------------------------- SIGPLAN Sponsorship POPL co-located events are sponsored by SIGPLAN (http://sigplan.org/) There are two kinds of co-located events: Conference-approved (no proceedings) and SIGPLAN-approved (proceedings in the ACM Digital Library). See http://www.sigplan.org/Resources/Guidelines/Workshops/ for more information, including a full listing of prescriptions for Conference-approved and SIGPLAN-approved workshops. SIGPLAN-approved workshops must respect the SIGPLAN Diversity Policy. Proposals for SIGPLAN-approved workshops must additionally include the gender, country of affiliation, and professional status of potential PC members. See https://www.sigplan.org/Resources/Policies/Diversity/ for more details. --------------------------------------------------------------------- Selection committee All submissions will be evaluated by a committee comprising the workshops co-chairs, the general chair, and the program chair. --------------------------------------------------------------------- Further information Any questions regarding POPL 2027 co-located event proposals should be addressed to the workshops chairs, Aws Albarghouthi (aws(a)cs.wisc.edu) and Alan Schmitt (alan.schmitt(a)inria.fr)

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POPL 2027 Call for Papers
by Ningning Xie 10 Jun '26

10 Jun '26

POPL 2027 Call for Papers Sun 10 - Sat 16 January 2027 Mexico City, Mexico https://popl27.sigplan.org/ ============================= PACMPL Issue POPL 2027 seeks contributions on all aspects of programming languages and programming systems, both theoretical and practical. Authors of papers published in PACMPL Issue POPL 2027 will be invited – but not required – to present their work in the POPL conference in January 2027, which is sponsored by ACM SIGPLAN, in cooperation with ACM SIGACT and ACM SIGLOG. **NEW FOR 2027** - Clarification about expectations concerning mechanized proofs; see Submission Guidelines: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers#submission-… - At least one author of each paper submission must be registered as a Reserve Reviewer as per the Reserve Reviewer Policy: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers#reserve-rev… See details: https://popl27.sigplan.org/track/POPL-2027-popl-research-papers ## Important Dates - Paper submission deadline: Thursday July 9, 2026 - Author response period: Mon 7 - Thu 10 Sep, 2026 - Author notification: Mon 5 Oct, 2026 - Revision deadline: Mon 26 Oct, 2026 - Final acceptance notification: Mon 9 Nov, 2026 - Camera ready deadline: Fri 20 Nov, 2026 ## Submission Site Information The submission site is https://popl27.hotcrp.com. Papers may be resubmitted to the submission site multiple times up until the deadline, but only the last version submitted before the deadline will be reviewed. There is no abstract deadline. The submission site requires entering author names and affiliations, relevant topics, and potential conflicts. Addition or removal of authors after the submission deadline will need to be approved by the Program Chair (as this kind of change potentially undermines the goal of eliminating conflicts during paper assignment). The submission deadline is 11:59PM July 9, 2026 anywhere on earth: https://en.wikipedia.org/wiki/Anywhere_on_Earth ## Scope Principles of Programming Languages (POPL) is a forum for the discussion of all aspects of programming languages and programming systems. Both theoretical and experimental papers are welcome, on topics ranging from formal frameworks to experience reports. We seek submissions that make principled, enduring contributions to the theory, design, understanding, implementation, or application of programming languages. ## Evaluation Criteria The Review Committee (aka Program Committee, PC) will evaluate the technical contribution of each submission as well as its accessibility to both experts and the general POPL audience. All papers will be judged on significance, originality, relevance, correctness, and clarity. Each paper must explain its scientific contribution in both general and technical terms, identifying what has been accomplished, explaining why it is significant and comparing it with previous work. Advice on writing technical papers can be found on the SIGPLAN author information page (https://www.sigplan.org/Resources/Author/) ## Double-Blind Reviewing POPL 2027 will use a full double-blind reviewing process (similar to the one used in recent years (POPL 2023 - 2026) but different from the lightweight double-blind process used before then). This means that identities of authors will not be made visible to reviewers until after conditional-acceptance decisions have been made, and then only for the conditionally-accepted papers. ## Important update on ACM’s new open access publishing model for ACM Conferences Starting January 1, 2026, ACM has fully transitioned to Open Access. All ACM publications, including those from ACM-sponsored conferences, will be 100% Open Access. Authors will have two primary options for publishing Open Access articles with ACM: the ACM Open institutional model or by paying Article Processing Charges (APCs). For a paper to be covered by ACM Open, the corresponding author must be affiliated with a participating institution. APC pricing for 2027 conferences is currently under review and will be finalized in June. With over 2,600 institutions already part of ACM Open, the majority of ACM-sponsored conference papers will not require APCs from authors or conferences. Authors from institutions not participating in ACM Open will need to pay an APC to publish their papers, unless they qualify for a waiver. To find out whether an APC applies to your article, please consult the list of participating institutions (https://libraries.acm.org/acmopen/open-participants) in ACM Open and review the APC Waivers and Discounts Policy ( https://www.acm.org/publications/policies/policy-on-open-access-apc-waivers… ).

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Richard Bird Distinguished Dissertation Award - Call for Nominations
by Graham Hutton (staff) 01 Jun '26

01 Jun '26

Dear all, I'm pleased to announce that JFP is establishing the Richard Bird Distinguished Dissertation Award, to recognise an outstanding PhD dissertation in functional programming. Please share! Best wishes, Graham Hutton ================================================================= CALL FOR NOMINATIONS Richard Bird Distinguished Dissertation Award 2025 Deadline: 31st August 2026 http://tinyurl.com/jfp-bird-award ================================================================= OVERVIEW The Journal of Functional Programming is pleased to establish the Richard Bird Distinguished Dissertation Award, to recognise an outstanding PhD dissertation in functional programming. Richard Bird (1943-2022) was one of the leading figures in functional programming. He was a Professor in Oxford, where he founded the Algebra of Programming group, and served as Director of the Computing Laboratory. Richard is renowned for his many books and pearls on functional programming, which set a lasting standard for clear and elegant writing. It seems fitting that an award be established in his name to further encourage these values in the field. The award includes a prize of £1,000. Funding for the prize is supported by a generous donation from Richard himself to further the cause of functional programming. CRITERIA Eligible dissertations must have been completed in 2025. Depending on the institution, this may be the date of the viva, corrections being approved, graduation ceremony, or otherwise. The award is open to all topics within the remit of JFP, with a particular emphasis on dissertations that reflect Richard's own values of clarity, simplicity and elegance. For a dissertation to be considered for the award it should: - Reach a high standard of exposition; - Make a noteworthy contribution to the subject; - Place the results in the wider context of computer science. NOMINATIONS Please submit the following information to the award chair, <graham.hutton(a)nottingham.ac.uk>, by 31st August 2026: - Two letters of support, explaining why the dissertation should be considered for the award. One letter should be from the advisor/supervisor, and one from an independent source with no conflict of interest with the candidate, such as an external examiner or other expert in the field. - A copy of the dissertation itself. AWARD COMMITTEE Graham Hutton (chair), University of Nottingham Matthew Flatt, University of Utah Jeremy Gibbons, University of Oxford François Pottier, INRIA Wouter Swierstra, University of Utrecht Ningning Xie, University of Toronto The JFP editors-in-chief serve as observers of the committee. ================================================================= This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

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