May 2024 - Haskell-Cafe

CGO'25 - Call for Papers
by Luisa Cicolini 22 May '24

22 May '24

IEEE/ACM International Symposium on Code Generation and Optimization (CGO<https://2025.cgo.org/>) Co-located with PPoPP<https://conf.researchr.org/series/PPoPP>, HPCA<https://hpca-conf.org/2025/> and CC<https://conf.researchr.org/series/CC> Las Vegas, USA The International Symposium on Code Generation and Optimization (CGO’25) will be held in Las Vegas, USA. CGO is the premier venue to bring together researchers and practitioners working at the interface of hardware and software on a wide range of optimization and code generation techniques and related issues. The conference spans the spectrum from purely static to fully dynamic approaches, and from pure software-based methods to specific architectural features and support for code generation and optimization. ________________________________ CGO now uses two submissions per year. This follows the model established by other conferences in our field in recent years, such as ASPLOS and OOPSLA. Papers submitted to the first round can either be directly accepted, rejected, or invited to submit a revised version of the paper to the second round. For papers invited to submit a revised version, authors will be given a list of revisions that should be acted on to improve the paper. We will make every effort to ensure that the revised paper is reviewed by the same referees, who will assess whether the revisions are satisfactory. If so, the paper will be accepted. If a paper is rejected, the authors may still submit a revised version in a subsequent round, which will be treated as a new submission. ________________________________ First Submission Deadline * Paper Submission: May 30, 2024 * Author Rebuttal Period: July 9-11, 2024 * Paper Notification: July 22, 2024 Second Submission Deadline * Paper Submission: September 12, 2024 * Author Rebuttal Period: October 22 - 24, 2024 * Paper Notification: November 4, 2024 Contacts: * Hugh Leather - Meta – hleather(a)meta.com<mailto:hleather@meta.com> * P. (Saday) Sadayappan – University of Utah – saday(a)cs.utah.edu<mailto:saday@cs.utah.edu> ________________________________ Topics Original contributions are solicited on, but not limited to, the following topics: * Code Generation, Translation, Transformation, and Optimization for performance, energy, virtualization, portability, security, or reliability concerns, and architectural support * Efficient execution of dynamically typed and higher-level languages * Optimization and code generation for emerging programming models, platforms, domain-specific languages * Dynamic/static, profile-guided, feedback-directed, and machine learning-based optimization * Static, Dynamic, and Hybrid Analysis for performance, energy, memory locality, throughput or latency, security, reliability, or functional debugging * Program characterization methods * Profiling and instrumentation techniques; architectural support * Novel and efficient tools * Compiler design, practice and experience * Compiler abstraction and intermediate representations * Vertical integration of language features, representations, optimizations, and runtime support for parallelism * Solutions that involve cross-layer (HW/OS/VM/SW) design and integration * Deployed dynamic/static compiler and runtime systems for general purpose, embedded system and Cloud/HPC platforms * Parallelism, heterogeneity, and reconfigurable architectures * Optimizations for heterogeneous or specialized targets, GPUs, SoCs, CGRA and Quantum Computers * Compiler support for vectorization, thread extraction, task scheduling, speculation, transaction, memory management, data distribution and synchronization Standard research papers must be written in the ACM format<https://www.acm.org/publications/proceedings-template>, and may have up to 11 pages, references excluded. Please ensure that you and your co-authors obtain an ORCID ID, so you can complete the publishing process for your accepted paper. ACM has been involved in ORCID from the start and we have recently made a commitment to collect ORCID IDs from all of our published authors<https://authors.acm.org/author-resources/orcid-faqs>. We are committed to improve author discoverability, ensure proper attribution and contribute to ongoing community efforts around name normalization; your ORCID ID will help in these efforts. By submitting your article to an ACM Publication, you are hereby acknowledging that you and your co-authors are subject to all ACM Publications Policies<https://www.acm.org/publications/policies>, including ACM's new Publications Policy on Research Involving Human Participants and Subjects<https://www.acm.org/publications/policies/research-involving-human-particip…>. Alleged violations of this policy or any ACM Publications Policy will be investigated by ACM and may result in a full retraction of your paper, in addition to other potential penalties, as per ACM Publications Policy. ________________________________ Call for Tool and Practical Experience Papers CGO has a second category of papers called “Tools and Practical Experience”. Papers in this category must either give a clear account of a tool’s functionality or summarize a practical experience with realistic case studies. The successful evaluation of an artifact is mandatory for a Tool Paper. Therefore, authors of work conditionally accepted as Tool Papers must submit an artifact to the Artifact Evaluation Committee. The successful evaluation of the artifact is a requirement for final acceptance. Practical experience papers are encouraged, but not required, to submit an artifact to the Artifact Evaluation process. The selection criteria for papers in this category are: * Originality: Papers should present CGO-related technologies applied to real-world problems with scope or characteristics that set them apart from previous solutions. * Usability: The presented Tools or compilers should have broad usage or applicability. They are expected to assist in CGO-related research, or could be extended to investigate or demonstrate new technologies. If significant components are not yet implemented, the paper will not be considered. * Documentation: The tool or compiler should be presented on a web-site giving documentation and further information about the tool. * Benchmark Repository: A suite of benchmarks for testing should be provided. * Availability: The tool or compiler should be available for public use. * Foundations: Papers should incorporate the principles underpinning Code Generation and Optimization (CGO). However, a thorough discussion of theoretical foundations is not required; a summary of such should suffice. * Artifact Evaluation: The submitted artifact must be functional and support the claims made in the paper. Submission of an artifact is mandatory for papers presenting a tool. Tool and Practical Experience papers abide by the same limit of 11 pages in the ACM format<https://www.acm.org/publications/proceedings-template>, references excluded, and are not distinguished in the final proceedings. We encourage shorter submissions that give account of how scientific ideas have been incorporated and used in practice. ________________________________ Geographic Diversity and Inclusion Authors of papers accepted for CGO 2025 are encouraged to present their work in person. However, to foster the participation of students and professionals from everywhere, CGO 2025 will allow the remote presentation of papers, if their authors are unable to travel to the conference venue for reasons beyond their control (e.g. visa issues). Additionally, the conference organization will try to make attendance of CGO 2025 affordable for as many people as possible, with a specific focus on students from universities located in under-represented countries who are paper authors. ________________________________ Artifact Evaluation The Artifact Evaluation process is run by a separate committee whose task is to assess how the artifacts support the work described in the papers. This process contributes to improved reproducibility in research that should be a great concern to all of us. There is also some evidence that papers with a supporting artifact receive higher citations than papers without artifact evaluation. Authors of accepted papers at CGO have the option of submitting their artifacts for evaluation within two weeks of paper acceptance. To ease the organization of the AE committee, we kindly ask authors to indicate at the time they submit the paper, whether they are interested in submitting an artifact. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Additional information is available on the CGO AE web page. Authors of accepted papers are encouraged, but not required, to make these materials publicly available upon publication of the proceedings. ________________________________ Authors should carefully consider the difference in focus between the co-located conferences when deciding where to submit a paper. CGO will make the proceedings freely available via the IEEE Xplore platform during the period from two weeks before to two weeks after the conference. This option will facilitate easy access to the proceedings by conference attendees, and it will also enable the community at large to experience the excitement of learning about the latest developments being presented in the period surrounding the event itself. ________________________________ Distinguished Paper Awards Up to 10% of papers accepted at CGO 2025 will be designated as Distinguished Papers, following the ACM policy. This award is open to both regular and tool papers.

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PLMW@PLDI 2024: Call for Lightning Talks on Research Group Openings
by Yao Li 21 May '24

21 May '24

Hi All. If you are attending PLDI this year, this might be of interest to you. We are experimenting with new ways of networking at PLMW@PLDI’24 through "Lightning talks on research group openings". If you have (or anticipate) an open position, either in academia or industry, full-time or part-time—you can now leverage PLMW to advertise that position. The definition of the opening is to be interpreted broadly. Towards this end, we would like to invite lightning talks describing the opportunities in your groups. At this point, we expect the talk to be anywhere between 5 to 10mins. Depending on the space, we may tighten the time to just 5mins closer to the program. Please fill this form <https://forms.gle/uHBQwzAmBR2GXLv29> by *June 5th* if you are interested. Note that the talks are in-person. The event is on *June 24, 2024*. You can check out https://pldi24.sigplan.org/track/PLMW-PLDI-2024 for more details on the PLMW program. Anitha Gollamudi Univ. of Massachusetts Lowell. https://sites.uml.edu/anitha-gollamudi/

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Priorities for upcoming GHC releases
by Zubin Duggal 21 May '24

21 May '24

Hi all, We detail our plans for upcoming GHC releases in a new blog post: https://www.haskell.org/ghc/blog/20240521-ghc-release-priorities.html The summary is that we will prioritise work on the 9.10, 9.6 and master branches over work on the 9.8 branch for the coming few months due to time and resource constraints. This does not mean that we are dropping support for GHC 9.8, but that releases in this series might be made at a slower pace than usual. Cheers, Zubin.

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POPL 2025: First Call for Papers (deadline: July 11 AOE)
by Ningning Xie 20 May '24

20 May '24

Dear all, Please find below the Call for Papers for the POPL 2025 conference. We would be grateful if you could help distribute this call among your networks. Many thanks! Ningning Xie POPL 2025 Publicity Chair PACMPL Issue POPL 2025 seeks contributions on all aspects of programming languages and programming systems, both theoretical and practical. Authors of papers published in PACMPL Issue POPL 2025 will be invited to present their work in the POPL conference in January 2025, which is sponsored by ACM SIGPLAN, in cooperation with ACM SIGACT and ACM SIGLOG. POPL 2025 Website: https://conf.researchr.org/home/POPL-2025 Call for Papers: https://conf.researchr.org/track/POPL-2025/POPL-2025-popl-research-papers#P… Double-Blind Review FAQ: https://conf.researchr.org/track/POPL-2025/POPL-2025-popl-research-papers#F… ### Organization Conference Location: Denver, Colorado, United States Conference Dates: January 19-25, 2025 General Chair: Steve Zdancewic, University of Pennsylvania Program Chair: Armando Solar-Lezama, MIT Program Committee: https://conf.researchr.org/committee/POPL-2025/POPL-2025-popl-research-pape… ### Important Dates All the times/deadlines below are Anywhere on Earth (AoE) in 2024. Submission deadline: July 11 ### 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 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/. Deadlines and formatting requirements, detailed below, will be strictly enforced. ### Double-Blind Reviewing Process POPL 2025 will use a full double-blind reviewing process (similar to the one used for POPL 2023 and 2024 but different from the lightweight double-blind process used in previous years). 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. The use of full double-blind reviewing has several consequences for authors. * **Submissions**: Authors must omit their names and institutions from their paper submissions. In addition, references to authors’ own prior work should be in the third person (e.g., not “We build on our previous work …” but rather “We build on the work of …”). * **Supplementary material**: Authors are permitted to provide supplementary material (e.g., detailed proofs, proof scripts, system implementations, or experimental data) along with their submission, which reviewers may (but are not required to) examine. This material may take the form of a single file, such as a PDF or a tarball. Authors must fully anonymize any supplementary material. * **Author response**: In responding to reviews, authors should not say anything that reveals their identity, since author identities will not be revealed to reviewers at that stage of the reviewing process. * **Dissemination of work under submission**: Authors are welcome to disseminate their ideas and post draft versions of their paper(s) on their personal website, institutional repository, or arXiv (reviewers will be asked to turn off arXiv notifications during the review period). But authors should not take steps that would almost certainly reveal their identities to members of the Program Committee, e.g., directly contacting PC members or publicizing the work on widely-visible social media or major mailing lists used by the community. The purpose of the above restrictions is to help the Program Committee and external reviewers come to a judgment about the paper without bias, not to make it impossible for them to discover the authors’ identities if they were to try. In particular, nothing should be done in the name of anonymity that weakens the quality of the submission. However, there are occasionally cases where adhering to the above restrictions is truly difficult or impossible for one reason or another. In such cases, the authors should contact the Program Chair to discuss the situation and how to handle it. The FAQ on Double-Blind Reviewing addresses many common scenarios and answers many common questions about this topic. But there remain many grey areas and trade-offs. If you have any doubts about how to interpret the double-blind rules or you encounter a complex case that is not clearly covered by the FAQ, please contact the Program Chair for guidance. ### Evaluation Process Like last year, POPL 2025 will use a double-blind reviewing process (instead of the lightweight double-blind process used in recent years). This means that identities of authors will not be visible to reviewers until after conditional-acceptance decisions have been made. For authors, the main change is that there is no option to upload non-anonymized supplementary material; only anonymized supplementary material may be submitted. POPL 2025 will have five Associate Chairs who will help the PC Chair monitor reviews, solicit external expert reviews for submissions when there is not enough expertise on the committee, and facilitate reviewer discussions. As in previous years, authors will have a multi-day period to respond to reviews, as indicated in the Important Dates table. Responses are optional. A response must be concise, addressing specific points raised in the reviews; in particular, it must not introduce new technical results. Reviewers will write a short reaction to these author responses. The Review Committee (RC) will discuss papers electronically, and will use synchronous virtual meetings to discuss any papers for which there is disagreement among reviewers, in some cases soliciting additional input from other experts in the committee. There is no formal External Review Committee, though experts outside the committee may be consulted for some papers. Reviews will be accompanied by a short summary of the reasons behind the committee’s decision with the goal of clarifying the reasons behind the decision. To conform with ACM requirements for journal publication, all POPL papers will be conditionally accepted; authors will be required to submit a short description of the changes made to the final version of the paper, including how the changes address any requirements imposed by the Review Committee. That the changes are sufficient will be confirmed by the original reviewers prior to acceptance to POPL. Authors of conditionally accepted papers must submit a satisfactory revision to the Review Committee by the requested deadline or risk rejection. For additional information about the reviewing process, see: [Principles of POPL](https://www.sigplan.org/Conferences/POPL/Principles/), a presentation of the underlying organizational and reviewing policies for POPL. For POPL 2025, policies specified in this Call for Papers supersede those in the Principles of POPL document. ### Submission Site Information The submission site is https://popl25.hotcrp.com. Authors can submit multiple times prior to the deadline. Only the last submission 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 11, 2024 anywhere on earth: https://en.wikipedia.org/wiki/Anywhere_on_Earth ### Conflicts of Interest For each submission, the authors must make sure that they properly declare all potential conflicts of interest for all of the authors of that submission. This includes marking PC conflicts as well as “Other Conflicts (external)”. A conflict caught late in the reviewing process leads to a voided review which may be infeasible to replace. Conflicts should be declared between an adviser and an advisee (e.g., Ph.D., post-doc; forever), between an author and a co-author (papers and proposals; for two years), between people at the same institution (branches of large companies or different locations of research institutes are considered to be the same institution; for two years after leaving an institution), between people with financial conflicts of interest, and between friends or relatives. Please do not declare spurious conflicts: such incorrect conflicts are especially harmful if the aim is to exclude potential reviewers, so spurious conflicts can be grounds for rejection. If you are unsure about a conflict, please consult the Program Chair. ### Submission Guidelines Prior to the paper submission deadline, authors should upload their full anonymized paper. Here are some key requirements concerning paper submissions: * Each paper should have no more than **25 pages of text, excluding bibliography**, using the PACMPL format (specifically, the `acmart` LaTeX class with `acmsmall` option). It is a single-column page layout with a 10 pt font, 12 pt line spacing, and wider margins than recent POPL page layouts. In this format, the main text block is 5.478 in (13.91 cm) wide and 7.884 in (20.03 cm) tall. Use of a different format (e.g., smaller fonts or a larger text block) is grounds for summary rejection. The PACMPL template for LaTeX can be found at the [SIGPLAN author information page]( https://www.sigplan.org/Resources/Author/) and further information about PACMPL submissions can be found on the [PACMPL author guidelines page]( https://dl.acm.org/journal/pacmpl/author-guidelines) PACMPL does not support submissions in Microsoft Word. * We strongly encourage use of the `review` and `screen` options in order to make submissions easier to review. * (**NEW this year**) Authors may choose which citation format they wish to use, which can be either author-year (the mandate for final versions in previous years) or numeric. * Submissions should be in PDF and printable on both US Letter and A4 paper. Papers may be resubmitted to the submission site multiple times up until the deadline, but the last version submitted before the deadline will be the version reviewed. * Submitted papers must adhere to the [SIGPLAN Republication Policy]( https://www.sigplan.org/Resources/Policies/Republication/) and the [ACM Policy on Plagiarism]( https://www.acm.org/publications/policies/plagiarism-overview) Concurrent paper submissions to other conferences, workshops, journals, or similar forums of publication are not allowed. * Authors are free to submit supplementary material along with their submissions, but it must be fully anonymized. * Authors must list all their conflicts of interest (both PC conflicts and external conflicts) in the HotCRP submission form. * Authors may include additional information in a field of the HotCRP submission form labeled "Confidential Comments for the Program Chair". This information need not be anonymized. It can be used to inform the Program Chair, for example, about sensitive issues concerning a conflict with a PC member or about supplementary material that cannot be anonymized. It is left to the discretion of the Program Chair what to do with this information. * If for some reason an author feels uncomfortable discussing a sensitive issue with the Program Chair (or communicating via the "Confidential Comments" field in HotCRP), they should feel free to get in touch instead with any of the Associate Chairs, with whom they can discuss the issue in confidence. * Submissions from PC members (except the Program Chair) are permitted and will not be handled any differently than other submissions. This is in accordance with a recent change in policy approved by the SIGPLAN Executive Committee: SIGPLAN conferences that use full double-blind review and whose PCs have at least 50 members need not hold PC submissions to a higher standard. ### Artifact Evaluation for Accepted Papers Authors of conditionally accepted papers will be invited to formally submit supporting materials to the Artifact Evaluation process. Artifact Evaluation is run by a separate committee whose task is to assess how the artifacts support the work described in the papers. Artifact submission is strongly encouraged but voluntary and will not influence the final decision regarding the papers. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Authors of accepted papers are encouraged to make these materials publicly available upon publication of the proceedings, by including them as “source materials” in the ACM Digital Library. ### Copyright, Publication, and Presentation As a Gold Open Access journal, PACMPL is committed to making peer-reviewed scientific research free of restrictions on both access and (re-)use. Authors are strongly encouraged to support libre open access by licensing their work with the [Creative Commons Attribution 4.0 International (CC BY) license](https://creativecommons.org/licenses/by/4.0/), which grants readers liberal (re-)use rights. Authors of accepted papers will be required to choose one of the following publication rights: * Author licenses the work with a [Creative Commons license]( https://creativecommons.org/) retains copyright, and (implicitly) grants ACM non-exclusive permission to publish (suggested choice). * Author retains copyright of the work and grants ACM a non-exclusive permission to publish license. * Author retains copyright of the work and grants ACM an exclusive permission to publish license. * Author transfers copyright of the work to ACM. These choices follow from ACM Copyright Policy and ACM Author Rights, corresponding to ACM's "author pays" option. While PACMPL may ask authors who have funding for open-access fees to voluntarily cover the article processing charge (currently, US$400), payment is not required for publication. PACMPL and SIGPLAN continue to explore the best models for funding open access, focusing on approaches that are sustainable in the long-term while reducing short-term risk. All papers will be archived by the ACM Digital Library. Authors will have the option of including supplementary material with their paper. The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. Authors of accepted papers are required to give a short talk (roughly 25 minutes long) at the conference, according to the conference schedule. However, authors who cannot attend in person will be provided with some option for remote presentation, as well as some mechanism for remote interaction with conference participants. ### Distinguished Paper Awards At most 10% of the accepted papers of POPL 2025 will be designated as Distinguished Papers. This award highlights papers that the Review Committee thinks should be read by a broad audience due to their relevance, originality, significance, and clarity. The selection of the distinguished papers will be made based on the final version of the paper and through an additional review process.

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tls transition from 1.9 to 2.0
by Ben Franksen 19 May '24

19 May '24

Hi everyone from 1.9.x to 2.0.x the tls package made a change to require EMS (extended main secret) by default. I must admit that I have no idea what this is about and I don't really care much. However, it turns out that for compatibility reasons I need to change it to the old behavior (which allowed but did not require it). So I wonder how to do that. The problem is that I am not using tls directly but only via http-conduit (we only need the http client side functionality and mostly for simple download of files). Any hints would be greatly appreciated. Cheers Ben -- I would rather have questions that cannot be answered, than answers that cannot be questioned. -- Richard Feynman

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problems with trace
by George Colpitts 18 May '24

18 May '24

After I load the following into ghci and call main I expect to see "norm" in the output 3 times as I have called it 3 times but it only shows once. Why? traceBug.hs --------------- {-# OPTIONS_GHC -Wall #-} import Debug.Trace (trace) norm :: [Int] -> [Int] norm = trace ("norm") id main :: IO () main = do print $ norm [2] print $ norm [2] print $ norm [3] --------------------- ghci session % ghci traceBug.hs Loaded package environment from /Users/gcolpitts/.ghc/x86_64-darwin-9.8.2/environments/default GHCi, version 9.8.2: https://www.haskell.org/ghc/ :? for help [1 of 2] Compiling Main ( traceBug.hs, interpreted ) Ok, one module loaded. ghci> main norm [2] [2] [3] ghci>

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cradle: a simpler process library
by Julian Arni 15 May '24

15 May '24

Hi all, We just released cradle, a library aimed at a being simpler and more intuitive subprocess library. More details in: - The announcement: https://garnix.io/blog/announcing-cradle - The hackage page: https://hackage.haskell.org/package/cradle-0.0.0.0/docs/Cradle.html Feedback welcome! Cheers, Julian

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[ANN] Copilot 3.19.1
by Frank Dedden 14 May '24

14 May '24

Hi everyone! We are very excited to announce Copilot 3.19.1 [1,2]. Copilot is a stream-based EDSL in Haskell for writing and monitoring embedded C programs, with an emphasis on correctness and hard realtime requirements. Copilot is typically used as a high-level runtime verification framework, and supports temporal logic (LTL, PTLTL and MTL), clocks and voting algorithms. Copilot marked as NASA Class D open-source software, and is being used at NASA in drone test flights. Through the NASA tool Ogma [3] (also written in Haskell), Copilot also serves as a runtime monitoring backend for NASA's Core Flight System, Robot Operating System (ROS2), and FPrime (the software framework used in the Mars Helicopter). This release does not contain any API breaking changes, but consists of some improvements to the copilot-theorem package. Thanks to Ryan Scott (Galois Inc.) a problem related to the interface with the Kind 2 model checker is fixed. Additionally, improvements have been made to the documentation. As always, we're releasing exactly 2 months since the last release. Our next release is scheduled for July 7th, 2024. Current emphasis is on improving the codebase in terms of stability and test coverage, removing unnecessary dependencies, hiding internal definitions, and formatting the code to meet our new coding standards. Additionally, as an ongoing process, work is being done on making Copilot more accessible to people less familiar with Haskell. Users are encouraged to participate by opening issues and asking questions via our github repo [4]. Happy Haskelling! Frank Dedden [1] https://github.com/Copilot-Language/copilot/releases/tag/v3.19.1 [2] https://hackage.haskell.org/package/copilot [3] https://github.com/nasa/ogma [4] https://github.com/Copilot-Language/copilot

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Preferred syntax for append
by Mark McConnell 14 May '24

14 May '24

We know that lists have map. Sometimes we want to take the higher perspective of Functor, replacing map with fmap, then replacing fmap with <$> . This post asks the corresponding question about append. The notation for append within List itself is ++ . Often we think of lists as Monads. Applicative generalizes Monad, and Alternative specializes Applicative. Alternative has <|> which behaves as ++ on List. I have been using <|> for this purpose. Recently, I have begun to read and enjoy "Effective Haskell". In Chapter 1, this book uses <> for append. Clearly they are thinking of List as a Semigroup. I'm curious about your thoughts on ++ versus <|> versus <> .

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Re: [Haskell-cafe] Preferred syntax for append
by Olaf Klinke 13 May '24

13 May '24

> Concatenation with (<>) is more meaningful and holds better semantics > than (<|>), described as just "An associative binary operation". (<>) is also "just an associative binary operation", no more guarantees than (<|>). That said, for append (<>) should be preferred over (<|>) because one can then switch to more efficient append implementations just by changing the type signature, e.g. when switching from String to Text: The former is an Alternative, the latter ist not. (<|>) for list models non-deterministic choice, which can be useful in combinatorial problems. Olaf

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