September 2023 - Haskell-Cafe

Re: [Haskell-cafe] Limitations of generalization of type constructors
by Ryan Scott 18 Sep '23

18 Sep '23

Short answer: This is expected behavior, and it's unlikely that behavior will change any time soon. Long answer: The key phrase in your original post is "the quantifier moved". That is, in this definition: > fc3 :: Int > fc3 = f (const 0) GHC will turn it into something like this behind the scenes when compiling it to Core: > fc3 :: Int > fc3 = f (\ (@z). const @Int @(Maybe z) 0 :: forall (z :: Type). Maybe z -> Int) Note the presence of `\ (@z)`, which binds a type variable with a lambda. This process of moving quantifiers by using type variables in lambdas is called *regeneralization*. A somewhat surprising fact is that GHC can only perform regeneralization some of the time. GHC can regeneralize type-level `forall`s—that is, `forall`s in the types of terms, as is the case in the example above—but it cannot regeneralize *kind*-level `forall`s. In your post, the `forall`s in the kinds of C2 and Const are kind-level `forall`s. This restriction is documented here [1] in the GHC User's Guide. I've also written a slightly longer blog post [2] about the topic. The reason why this restriction exists is because there is no type-level counterpart to `\ (@z)` in Core, which would be required for regeneralization at the kind level. Adding type-level lambdas to Core would likely be a non-trivial effort. The UnsaturatedTypeFamilies proposal [3], which proposes to relax some restrictions about when types can appear partially applied, is the closest thing that I can think of, but it stops short of proposing full type-level lambdas. Best, Ryan ----- [1] https://downloads.haskell.org/ghc/9.6.2/docs/users_guide/exts/poly_kinds.ht… [2] https://ryanglscott.github.io/2019/07/10/the-surprising-rigidness-of-higher… [3] https://github.com/ghc-proposals/ghc-proposals/blob/7e380dcc4494de30f95bd15…

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Re: [Haskell-cafe] Why can't I promote data family constructors, and what to do instead?
by Ryan Scott 18 Sep '23

18 Sep '23

Regarding the first question ("Is this restriction *really* necessary?"), I think the answer is likely "no", at least for most data family instances. This discussion [1] is the most up-to-date reference on the history and motivations behind the current restriction. In that discussion, it is hypothesized that data family instances whose data constructors do not use any constraints could be promoted without needing to rethink how Core works. (If I understand correctly, all of your data family instances fall into this simple subset.) This discussion could provide a template for a GHC proposal that proposes to allow this feature. Best, Ryan ----- [1] https://github.com/ghc-proposals/ghc-proposals/discussions/456

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Limitations of generalization of type constructors
by Tom Ellis 18 Sep '23

18 Sep '23

Hello Cafe, Generalization of types in type constructors behaves strangely compared to the same behaviour at the term level. I was wondering whether this is expected, whether it's a known issue that's due to be resolved, or is a known issue that can't be resolved for some technical reason. This mail is a literate Haskell file. > {-# LANGUAGE DataKinds #-} > {-# LANGUAGE PolyKinds #-} > {-# LANGUAGE RankNTypes #-} > {-# LANGUAGE StandaloneKindSignatures #-} > {-# LANGUAGE TypeFamilies #-} > > {-# OPTIONS_GHC -Wall #-} > {-# OPTIONS_GHC -Wno-unticked-promoted-constructors #-} > > import Prelude hiding (const) > import Data.Kind (Type) `f` takes an argument of polymorphic type > f :: (forall (z :: Type). Maybe z -> Int) -> Int > f k = k (Just True) `c1` is an argument that will fit there. Its type matches exactly. > c1 :: forall (z :: Type). Maybe z -> Int > c1 _ = 0 > > fc1 :: Int > fc1 = f c1 `c2` will fit there but its type doesn't match exactly. `z` will have to be substituted with `Maybe z`, obtaining the type forall (z :: Type). Maybe z -> Int which does fit exactly. > c2 :: forall (z :: Type). z -> Int > c2 _ = 0 > > fc2 :: Int > fc2 = f c2 `const` will fit there, once `z` is substituted with `Maybe z`, the `Int` argument applied and the quantifer moved, obtaining the type forall (z :: Type). Maybe z -> Int which does fit exactly. > const :: forall (z :: Type). Int -> z -> Int > const x _ = x > > fc3 :: Int > fc3 = f (const 0) The story for type constructors is not so pleasant. I can define an analogue of `f` on the type level: > type F :: (forall (z :: Type). Maybe z -> Type) -> Type > newtype F k = F (k (Just Bool)) and the analogue of `c1` fits exactly: > type C1 :: forall (z :: Type). Maybe z -> Type > data C1 m = C1 > > type FC1 :: Type > type FC1 = F C1 but the analogue of `c2` does not: > type C2 :: forall (z :: Type). z -> Type > data C2 m = C2 > > -- Occurs check: cannot construct the infinite kind: z ~ Maybe z > -- type FC2 :: Type > -- type FC2 = F C2 nor does the analogue of `const`: > type Const :: forall (z :: Type). Type -> Maybe z -> Type > newtype Const z a = Const z > > -- • Expected kind ‘forall z. Maybe z -> *’, > -- but ‘Const ()’ has kind ‘Maybe a0 -> *’ > -- type FC3 :: Type > -- type FC3 = F (Const ()) To get the analogue of `const` we have to be much more specific: > type OtherConst :: Type -> forall (z :: Type). Maybe z -> Type > newtype OtherConst z b = OtherConst z > > type FC4 :: Type > type FC4 = F (OtherConst ()) This is rather unfortunate because it limits generic programming at the type level!

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Why can't I promote data family constructors, and what to do instead?
by Tom Ellis 16 Sep '23

16 Sep '23

Hello Cafe, I'm confused why I can't promote data family constructors, and what I should do instead. This message is a literate Haskell file. > {-# LANGUAGE DataKinds #-} > {-# LANGUAGE StandaloneKindSignatures #-} > {-# LANGUAGE TypeFamilies #-} I can promote constructors of normal data types nicely, here CT1 is promoted > data T = CT1 Char > type PT1 = CT1 'x' Suppose I want to promote constructors of a "non uniform" data definition, that is one where the structure of the type depends on a type argument, In Haskell that means a GADT, type family or data family. For my purposes a type family is unsuitable. I need to be able to reference it unsaturated. A GADT is also unsuitable because it introduces extra runtime tags that I don't want. But nor do data families work because their constructors can't be promoted. > data family DF a > newtype instance DF Int = CDFInt1 Char > data instance DF Bool = CDFBool1 | CDFBool2 > > -- • Data constructor ‘CDFInt1’ cannot be used here > -- (it comes from a data family instance) > -- type PDF = CDFInt1 'x' The GHC users guide says Data family instance constructors cannot be promoted at the moment. GHC’s type theory just isn’t up to the task of promoting data families, which requires full dependent types. https://downloads.haskell.org/ghc/9.6.2/docs/users_guide/exts/data_kinds.ht… I'm puzzled about why I can't do that. I can do this > newtype DFInt = CDFInt1' Char > data DFBool = CDFBool1' | CDFBool2' > type family TF a > type instance TF Int = DFInt > type instance TF Bool = DFBool > type PNF1 :: TF Int > type PNF1 = CDFInt1' 'x' which I said above is unsuitable because I can't refer to `TF` unsaturated. But I can apply a standard trick of wrapping a type family in a newtype: > newtype NF a = CNF (TF a) > type PNF :: NF Int > type PNF = CNF (CDFInt1' 'x') Problem solved! But this goes all round the houses. What a mess! The data family version would be much neater if it worked. I have two questions: 1. Is this restriction *really* necessary? I'm surprised that GHC can't cope with promoting constructors of data families given that it is straightforward to simulate the desired behaviour with type families and a newtype. 2. Is my encoding the simplest that I can achieve? Note that the following GADT does *not* work because `GDFInt` has an unnecessary tag. > data GF a where > GDFInt :: Char -> GF Int > GDFBool1 :: GF Bool > GDFBool2 :: GF Bool

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[ANN] Jacinda 2.0.1.0
by Vanessa McHale 13 Sep '23

13 Sep '23

Hello all, I have released another iteration of Jacinda, a text-processing language that lets you filter (fits in with sed + awk), handy on Unix! I’ve rewritten the backend so it should have far fewer bugs! https://github.com/vmchale/jacinda/releases/tag/2.0.1.0 Cheers, Vanessa McHale

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ANN: shelltestrunner 1.10
by Simon Michael 12 Sep '23

12 Sep '23

I'm pleased to announce shelltestrunner 1.10 ! shelltestrunner (executable: `shelltest`) is a portable, GPLv3+ command-line tool for testing command-line programs or shell commands. It reads simple test specifications defining a command to run, some input, and the expected output, stderr, and exit status. It can run tests in parallel, selectively, with a timeout, in color, etc. The last release was 1.9, in 2018. The 1.10 release has been overdue; it brings some useful improvements, notably --print mode (with which you can convert old format 1 tests to the cleaner, recommended format 3), and precise line number reporting (to quickly locate the failing test). User-visible changes in 1.10 (2023-09-12): * GHC 9.6 compatibility (Andreas Abel) * Add --print for printing tests and/or converting file format (#24, Jakob Schöttl) * Add --shell option to select shell (#17, FC Stegerman) * Fix format1's handling of angle brackets in test data (#16) * Print test line number on failure (#14, Taavi Väljaots) * Add -p short flag for --precise * -h means --help, not --hide-successes * Clarify 300 char regex limit message Other changes: * Set up CI testing (#18 FC Stegerman, Simon Michael) * Improve bash-related tests (#20, FC Stegerman, Simon Michael) * Improved tests Thanks to release contributors: Jakob Schöttl, Taavi Väljaots, Felix C. Stegerman, and Andreas Abel. Install: $ stack install shelltestrunner-1.10 or: $ cabal update && cabal install shelltestrunner-1.10 Home: https://github.com/simonmichael/shelltestrunner

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SPLASH 2023 Call for Participation
by Alcides Fonseca 12 Sep '23

12 Sep '23

====================================================================== Call For Participation ACM Conference on Systems, Programming, Languages, and Applications: Software for Humanity (SPLASH'23) October 22-27, 2023, Cascais, Portugal https://2023.splashcon.org/ Follow us on Twitter @splashcon ====================================================================== The ACM SIGPLAN conference on Systems, Programming, Languages and Applications: Software for Humanity (SPLASH) embraces all aspects of software construction and delivery to make it the premier conference at the intersection of programming, languages, and software engineering. ====================================================================== # Participation ====================================================================== The registration information, including the link to registration form is available at https://2023.splashcon.org/attending/Registration ====================================================================== # List of Keynotes/Invited Talks ====================================================================== SPLASH will feature three keynotes: Amal Ahmed, Northeastern University, USA Dimitrios Vytiniotis, DeepMind, UK Joe Hellerstein, UC Berkeley, USA SPLASH co-located events include a number of speakers: Andreas Rossberg, Independent, Germany (MPLR) Manuel Hermenegildo, IMDEA, Spain (LOPSTR) Maribel Fernández, King's College London, UK (PPDP+LOPSTR) Delia Kesner, Université Paris Cité, France (PPDP) Daniel Kaestner, AbsInt, Germany (SAS) Gagandeep Singh, University of Illinois Urbana-Champaign, USA (SAS) Bor-Yuh Evan Chang, University of Colorado Boulder & Amazon, USA (SAS) Loris D’Antoni, University of Wisconsin, Madison, USA (SAS) ====================================================================== # List of Events ====================================================================== ** OOPSLA Research Papers ** Papers that address any aspect of software development are welcome, including requirements, modelling, prototyping, design, implementation, generation, analysis, verification, testing, evaluation, maintenance, reuse, replacement, and retirement of software systems. Papers may address these topics in a variety of ways, including new tools (such as languages, program analyses, and runtime systems), new techniques (such as methodologies, design processes, code organization approaches, and management techniques), and new evaluations (such as formalisms and proofs, corpora analyses, user studies, and surveys). ** Onward! Research Papers ** Onward! is a premier multidisciplinary conference focused on everything to do with programming and software: including processes, methods, languages, communities, and applications. Onward! is more radical, more visionary, and more open than other conferences to ideas that are well-argued but not yet proven. We welcome different ways of thinking about, approaching, and reporting on programming language and software engineering research. ** Onward! Essays ** Onward! Essays conference is looking for clear and compelling pieces of writing about topics important to the software community construed broadly. An essay can be an exploration of a topic, its impact, or the circumstances of its creation; it can present a personal view of what is, explore a terrain, or lead the reader in an act of discovery; it can be a philosophical digression or a deep analysis. It can describe a personal journey, perhaps that by which the author reached an understanding of such a topic. The subject area should be interpreted broadly and can include the relationship of software to human endeavours, or its philosophical, sociological, psychological, historical, or anthropological underpinnings. ** PLMW@SPLASH ** The SPLASH 2023 Programming Languages Mentoring Workshop encourages graduate students (PhD and MSc) and senior undergraduate students to pursue research in programming languages. This workshop will provide mentoring sessions on how to prepare for and thrive in graduate school and in a research career, focusing both on cutting-edge research topics and practical advice. The workshop brings together leading researchers and junior students in an inclusive environment in order to help welcome newcomers to our field of programming languages research. The workshop will show students the many paths that they might take to enter and contribute to our research community. ====================================================================== ** Workshops ** ====================================================================== **** CONFLANG **** CONFLANG is a workshop on the design, the theory, the practice and the future evolution of configuration languages. It aims to gather the emerging community in this area in order to engage in fruitful interactions, to share ideas, results, opinions, and experiences on languages for configuration. Correct configuration is an actual industrial problem, and would greatly benefit from existing and ongoing academic research. Dually, this is a space with new challenges to overcome and new directions to explore, which is a great opportunity to confront new ideas with large-scale production. **** FTSCS **** The aim of this workshop is to bring together researchers and engineers who are interested in the application of formal and semi-formal methods to improve the quality of safety-critical computer systems. FTSCS strives to promote research and development of formal methods and tools for industrial applications, and is particularly interested in industrial applications of formal methods. **** HATRA **** Programming language designers seek to provide strong tools to help developers reason about their programs. For example, the formal methods community seeks to enable developers to prove correctness properties of their code, and type system designers seek to exclude classes of undesirable behavior from programs. The security community creates tools to help developers achieve their security goals. In order to make these approaches as effective as possible for developers, recent work has integrated approaches from human-computer interaction research into programming language design. This workshop brings together programming languages, software engineering, security, and human-computer interaction researchers to investigate methods for making languages that provide stronger safety properties more effective for programmers and software engineers. **** IWACO **** Many techniques have been introduced to describe and reason about stateful programs, and to restrict, analyze, and prevent aliases. These include various forms of ownership types, capabilities, separation logic, linear logic, uniqueness, sharing control, escape analysis, argument independence, read-only references, linear references, effect systems, and access control mechanisms. These tools have found their way into type systems, compilers and interpreters, runtime systems and bug-finding tools. Their immediate practical relevance is self-evident from the popularity of Rust, a programming language built around reasoning about aliasing and ownership to enable static memory management and data race freedom, voted the "most beloved" language in the annual Stack Overflow Developer Survey seven times in a row. **** LIVE **** Programming is cognitively demanding, and too difficult. LIVE is a workshop exploring new user interfaces that improve the immediacy, usability, and learnability of programming. Whereas PL research traditionally focuses on programs, LIVE focuses more on the activity of programming. Our goal is to provide a supportive venue where early-stage work receives constructive criticism. Whether graduate students or tenured faculty, researchers need a forum to discuss new ideas and get helpful feedback from their peers. Towards that end, we will allot about ten minutes for discussion after every presentation. **** PAINT **** Programming environments that integrate tools, notations, and abstractions into a holistic user experience can provide programmers with better support for what they want to achieve. These programming environments can create an engaging place to do new forms of informational work - resulting in enjoyable, creative, and productive experiences with programming. In the workshop on Programming Abstractions and Interactive Notations, Tools, and Environments (PAINT), we want to discuss programming environments that support users in working with and creating notations and abstractions that matter to them. We are interested in the relationship between people centric notations and general-purpose programming languages and environments. How do we reflect the various experiences, needs, and priorities of the many people involved in programming — whether they call it that or not? **** PLF **** Applications supporting multi-device are ubiquitous. While most of the distributed applications that we see nowadays are cloud-based, avoiding the cloud can lead to privacy and performance benefits for users and operational and cost benefits for companies and developers. Following this idea, Local-First Software runs and stores its data locally while still allowing collaboration, thus retaining the benefits of existing collaborative applications without depending on the cloud. Many specific solutions already exist: operational transformation, client-side databases with eventually consistent replication based on CRDTs, and even synchronization as a service provided by commercial offerings, and a vast selection of UI design libraries. However, these solutions are not integrated with the programming languages that applications are developed in. Language based solutions related to distribution such as type systems describing protocols, reliable actor runtimes, data processing, machine learning, etc., are designed and optimized for the cloud not for a loosely connected set of cooperating devices. This workshop aims at bringing the issue to the attention of the PL community, and accelerating the development of suitable solutions for this area. **** REBELS **** Reactive programming and event-based programming are two closely related programming styles that are becoming ever more important with the advent of advanced HPC technology and the ever increasing requirement for our applications to run on the web or on collaborating mobile devices. A number of publications on middleware and language design — so-called reactive and event-based languages and systems (REBLS) — have already seen the light, but the field still raises several questions. For example, the interaction with mainstream language concepts is poorly understood, implementation technology is in its infancy and modularity mechanisms are almost totally lacking. Moreover, large applications are still to be developed and patterns and tools for developing reactive applications is an area that is vastly unexplored. This workshop will gather researchers in reactive and event-based languages and systems. The goal of the workshop is to exchange new technical research results and to define better the field by coming up with taxonomies and overviews of the existing work. **** ST30 **** Session types are a type-theoretic approach to specifying communication protocols so that they can be verified by type-checking. This year marks 30 years since the first paper on session types, by Kohei Honda at CONCUR 1993. Since then the topic has attracted increasing interest, and a substantial community and literature have developed. Google Scholar lists almost 400 articles with "session types" in the title, and most programming language conferences now include several papers on session types each year. In terms of the technical focus, there have been continuing theoretical developments (notably the generalisation from two-party to multi-party session types by Honda, Yoshida and Carbone in 2008, and the development of a Curry-Howard correspondence with linear logic by Caires and Pfenning in 2010) and a variety of implementations of session types as programming language extensions or libraries, covering (among others) Haskell, OCaml, Java, Scala, Rust, Python, C#, Go. ST30 is a workshop to celebrate the 30th anniversary of session types by bringing together the community for a day of talks and technical discussion. **** VMIL **** The concept of Virtual Machines is pervasive in the design and implementation of programming systems. Virtual Machines and the languages they implement are crucial in the specification, implementation and/or user-facing deployment of most programming technologies. The VMIL workshop is a forum for researchers and cutting-edge practitioners in language virtual machines, the intermediate languages they use, and related issues. The workshop is intended to be welcoming to a wide range of topics and perspectives, covering all areas relevant to the workshop’s theme. ====================================================================== ** SPLASH Posters ** ====================================================================== The SPLASH Posters track provides an excellent forum for authors to present their recent or ongoing projects in an interactive setting, and receive feedback from the community. SPLASH posters cover any aspect of programming, systems, languages and applications. The goal of the poster session is to encourage and facilitate small groups of individuals interested in a technical area to gather and interact. It is held early in the conference, to promote continued discussion among interested parties. ====================================================================== ** Doctoral Symposium ** ====================================================================== The SPLASH Doctoral Symposium provides students with useful guidance for completing their dissertation research and beginning their research careers. The symposium will provide an interactive forum fordoctoral students who have progressed far enough in their research to have a structured proposal, but will not be defending their dissertation in the next 12 months. ====================================================================== ** Student Research Competition ** ====================================================================== The ACM Student Research Competition (SRC), sponsored by Microsoft Research, offers a unique opportunity for undergraduate and graduate students to present their research to a panel of judges and conference attendees at SPLASH. The SRC provides visibility and exposes up-and-coming researchers to computer science research and the research community. This competition also gives students an opportunity to discuss their research with experts in their field, get feedback, and sharpen their communication and networking skills. ====================================================================== ** SPLASH-E ** ====================================================================== SPLASH-E is a forum for educators to make connections between programming languages research and the ways we educate computer science students. We invite work that could improve or inform computer science educators, especially work that connects with introductory computer science courses, programming languages, compilers, software engineering, and other SPLASH-related topics. Educational tools, experience reports, and new curricula are all welcome. ====================================================================== *** Co-Located Events *** ====================================================================== **** Dynamic Languages Symposium (DLS) **** The Dynamic Languages Symposium (DLS) is the premier forum for researchers and practitioners to share research and experience on all aspects of dynamic languages. After two decades of dynamic language research and DLS, it is time to reflect and look forward to what the next two decades will bring. This year's DLS will therefore be a special DLS focusing on the Future of Dynamic Languages. To do the notion of "symposium" justice, we will actively invite speakers to present their opinions on where Dynamic Languages might be, will be, or should be going in the next twenty years. **** Generative Programming: Concepts & Experiences (GPCE)**** ACM SIGPLAN International Conference on Generative Programming: Concepts & Experiences (GPCE) is a venue for researchers and practitioners interested in techniques that use program generation, domain-specific languages, and component deployment to increase programmer productivity, improve software quality, and shorten the time-to-market of software products. In addition to exploring cutting-edge techniques of generative software, our goal is to foster further cross-fertilization between the software engineering and the programming languages research communities. **** Logic-based Program Synthesis and Transformation (LOPSTR)**** The aim of the LOPSTR series is to stimulate and promote international research and collaboration on logic-based program development. LOPSTR is open to contributions in logic-based program development in any language paradigm. LOPSTR has a reputation for being a lively, friendly forum for presenting and discussing work in progress. **** Managed Programming Languages & Runtimes (MPLR)**** The 20th International Conference on Managed Programming Languages & Runtimes (MPLR'23, formerly ManLang, originally PPPJ) is a premier forum for presenting and discussing novel results in all aspects of managed programming languages and runtime systems, which serve as building blocks for some of the most important computing systems around, ranging from small-scale (embedded and real-time systems) to large-scale (cloud-computing and big-data platforms) and anything in between (mobile, IoT, and wearable applications). **** Principles and Practice of Declarative Programming (PPDP) **** PPDP aims to provide a forum that brings together researchers from the declarative programming communities, including those working in the logic, constraint and functional programming paradigms, but also embracing a variety of other paradigms such as visual programming, executable specification languages, database languages, AI languages and knowledge representation languages used, for example, in the semantic web. The goal is to stimulate research in the use of logical formalisms and methods for specifying, performing, and analysing computations, including mechanisms for mobility, modularity, concurrency, object-orientation, security, and static analysis. Papers related to the use of declarative paradigms and tools in industry and education are especially solicited. **** Static Analysis Symposium (SAS) **** Static Analysis is widely recognized as a fundamental tool for program verification, bug detection, compiler optimization, program understanding, and software maintenance. The series of Static Analysis Symposia has served as the primary venue for the presentation of theoretical, practical, and application advances in the area. ====================================================================== # Organizing Committee SPLASH 2023: ====================================================================== General Chair: Vasco T. Vasconcelos (University of Lisbon) OOPSLA Review Committee Chair: Mira Mezini (TU Darmstadt) OOPSLA Publications Co-Chair: Ragnar Mogk (TU Darmstadt) OOPSLA Artifact Evaluation Co-Chair: Benjamin Greenman (Brown University) OOPSLA Artifact Evaluation Co-Chair: Guillaume Baudart (INRIA) DLS General Chair: Stefan Marr (University of Kent) GPCE General Chair: Bernhard Rumpe (RWTH Aachen University) GPCE PC Chair: Amir Shaikhha (University of Edinburgh) LOPSTR PC Chair: Robert Glück (University of Copenhagen, Denmark) LOPSTR PC Chair: Bishoksan Kafle (IMDEA) MPLR General Chair: Rodrigo Bruno (University of Lisbon) MPLR PC Chair: Elliot Moss (University of Massachusetts Amherst) PPDP PC Chair: Santiago Escobar (Universitat Politècnica de València ) SAS Co-Chair: Manuel Hermenegildo (Technical University of Madrid & IMDEA) SAS Co-Chair: José Morales (IMDEA) SAS Artifact Evaluation Chair: Marc Chevalier (Snyk) SLE Chair: João Saraiva (University of Minho) SLE PC Co-Chair: Thomas Degueule (CNRS, LaBRI) SLE PC Co-Chair: Elizabeth Scott (Royal Holloway University of London) Onward! Papers Chair: Tijs van der Storm (CWI & University of Groningen) Onward! Essays Chair: Robert Hirschfeld (University of Potsdam; Hasso Plattner Institute) SPLASH-E Co-Chair: Molly Feldman (Oberlin College) Posters Co-Chair: Xujie Si (University of Toronto) Workshops Co-Chair: Mehdi Bagherzadeh (Oakland University) Workshops Co-Chair: Amin Alipour (University of Houston) Hybridisation Co-Chair: Youyou Cong (Tokyo Institute of Technology) Hybridisation Co-Chair: Jonathan Immanuel Brachthäuser (University of Tübingen) Video Co-Chair: Guilherme Espada (University of Lisbon) Video Co-Chair: Apoorv Ingle (University of Iowa) Video Co-Chair: John Hui (Columbia University) Publicity Chair, Web Co-Chair: Andreea Costea (National University Of Singapore) Publicity Chair, Web Co-Chair: Alcides Fonseca (University of Lisbon) PLMW Co-Chair: Molly Feldman (Oberlin College) PLMW Co-Chair: Youyou Cong (Tokyo Institute of Technology) PLMW Co-Chair: João Ferreira (University of Lisbon) Sponsoring Co-Chair: Bor-Yuh Evan Chang (University of Colorado Boulder & Amazon) Sponsoring Co-Chair: Nicolas Wu (Imperial College London) Student Research Competition Co-Chair: Xujie Si (McGill University, Canada) Local Organizer Chair: Diana Costa (University of Lisbon) SIGPLAN Conference Manager: Neringa Young ======================================================================

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OOPSLA 2024: Round 1 Call for Papers
by Umar Farooq 11 Sep '23

11 Sep '23

======================================================================== PACMPL Issue OOPSLA 2024 Call for Papers OOPSLA 2024 will be held as part of The ACM Conference on Systems, Programming, Languages, and Applications: Software for Humanity (SPLASH'24) October 20-25, 2024, Pasadena, California, United States https://2024.splashcon.org/track/splash-2024-oopsla ======================================================================== ### Important dates #### ROUND 1: Submission Deadline: Fri Oct 20, 2023 Author Response: Mon Dec 11 - Wed Dec 13, 2023 Author Notification: Fri Dec 22, 2023 Artifact Submission: Fri Jan 5, 2024 Artifact kick-tires: Sat Jan 6 - Fri Jan 19, 2024 Submission of Revisions: Sun Feb 11, 2024 Author Notification of Revisions: Sat Feb 24, 2024 Artifact Notification: Fri Mar 1, 2024 Camera Ready: Fri Mar 8, 2024 #### ROUND 2: Submission Deadline: Fri Apr 5, 2024 Author Response: Mon Jun 3 - Wed Jun 5, 2024 Author Notification: Fri Jun 21, 2024 Artifact Submission: Fri Jul 5, 2024 Artifact kick-tires: Sat Jul 6 - Fri Jul 19, 2024 Submission of Revisions: Sun Aug 4, 2024 Author Notification of Revisions: Sun Aug 18, 2024 Artifact Notification: Fri Aug 23, 2024 Camera Ready: Sun Sep 1, 2024 Papers accepted at either of the rounds will be published in the 2024 volume of PACMPL(OOPSLA) and invited to be presented at the SPLASH conference in October 2024. ### Scope The OOPSLA issue of the Proceedings of the ACM on Programming Languages (PACMPL) welcomes papers focusing on all practical and theoretical investigations of programming languages, systems and environments. Papers may target any stage of software development, including requirements, modelling, prototyping, design, implementation, generation, analysis, verification, testing, evaluation, maintenance, and reuse of software systems. Contributions may include the development of new tools, techniques, principles, and evaluations. #### Review Process PACMPL(OOPSLA) has two rounds of reviewing with submission deadlines around October and April each year. As you submit your paper you will receive around three reviews and an opportunity to provide an author response that will be read and addressed by the reviewers in the final decision outcome summary. There are 5 possible outcomes at the end of the round: *Accept*: Your paper will appear in the upcoming volume of PACMPL (OOPSLA). *Conditional Accept*: You will receive a list of required revisions that you will need to address. You must submit a revised paper, a clear explanation of how your revision addresses these comments, and "if possible" a diff of the PDF as supplementary material. Assuming you meet the listed requirements, after further review by the same reviewers, your paper will very likely be accepted. This process *has to be completed within two months of the initial decision* for the paper to be accepted, so we encourage timely turnaround in case revisions take more than one cycle to be accepted. *Minor Revision*: The reviewers have concerns that go beyond what can be enumerated in a list. Therefore, while you may receive a list of revisions suggested by the reviewers, this will not necessarily be comprehensive. You will have the opportunity to resubmit your revised paper and have it re-reviewed by the same reviewers, which may or may not result in your paper's acceptance. When you resubmit, you should clearly explain how the revisions address the comments of the reviewers, by including a document describing the changes and "if possible" a diff of the PDF as supplementary material. This process *has to be completed within two months of the initial decision* for the paper to be accepted in the current round, so we encourage timely turnaround in case revisions take more than one cycle to be accepted. *Major Revision*: You will receive a list of revisions suggested by the reviewers. Papers in this category are *invited to submit a revision to the next round of submissions* with a specific set of expectations to be met. When you resubmit, you should clearly explain how the revisions address the comments of the reviewers, by including a document describing the changes and "if possible" a diff of the PDF as supplementary material. The revised paper will be re-evaluated in the next round. Resubmitted papers will retain the same reviewers throughout the process to the extent possible. *Reject*: Rejected papers will not be included in the upcoming volume of PACMPL(OOPSLA). Papers in this category are not guaranteed a review if resubmitted less than one year from the date of the original submission. A paper will be judged to be a resubmission if it is substantially similar to the original submission. The Chairs will decide whether or not a paper is a resubmission of the same work. ### Submissions Submitted papers must be at most **23 pages** in 10 point font. There is no page limit on references. No appendices are allowed on the main paper, instead authors can upload supplementary material with no page or content restrictions, but reviewers may choose to ignore it. Submissions must adhere to the "ACM Small" template available from [the ACM](http://www.acm.org/publications/authors/submissions). Papers are expected to use author-year citations. 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Submissions are expected to comply with the [ACM Policies for Authorship](https://www.acm.org/publications/authors/information-for-author…. #### Artifacts Authors should indicate with their initial submission if an artifact exists, describe its nature and limitations, and indicate if it will be submitted for evaluation. Accepted papers that fail to provide an artifact will be requested to explain the reason they cannot support replication. It is understood that some papers have no artifacts. Please note that the artifact submission deadline will be following closely the paper submission deadline so make sure you check the Artifact Call as soon as you submit your paper to PACMPL(OOPSLA). ##### Data-Availability Statement To help readers find data and software, OOPSLA recommends adding a section just before the references titled Data-Availability Statement. If the paper has an artifact, cite it here. If there is no artifact, this section can explain how to obtain relevant code. 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S. Oliveira, U. Hong Kong, Hong Kong Burcu Kulahcioglu Ozkan, Delft University of Technology, The Netherlands Casper Bach Poulsen, Delft University of Technology, Netherlands Colin Gordon, Drexel University, USA Corina Pasarenau, NASA, USA Cyrus Omar, University of Michigan, USA Damien Zufferey, Sonar Source, Switzerland Dana Drachsler Cohen, Technion, Israel David Darais, Galois, USA David Pearce, ConsenSys, New Zealand Di Wang, Peking University, China Emma Söderberg, Lund University, Sweden Emma Tosch, Northeastern University, USA Fabian Muehlboeck, Australian National University, Australia Fei He, Tsinghua University, China Filip Niksic, Google, USA Fredrik Kjolstad, Stanford University, USA Guido Salvaneschi, University of St. Gallen, Switzerland Hila Peleg, Technion, Israel Jiasi Shen, The Hong Kong University of Science and Technology, China (Hong Kong) Jonathan Bell, Northeastern University, USA Jonathan Brachthäuser, University of Tübingen, Germany Joseph Tassarotti, New York University, USA Justin Hsu, Cornell University, USA Karine Even-Mendoza, King's College London, UK Kenji Maillard, Inria Rennes, France Matthew Flatt, U. Utah, USA Matthew Parkinson, Microsoft, UK Max Schaefer, GitHub, UK Michael Coblenz, UCSD, USA Milos Gligoric, UT Austin, USA Minseok Jeon, Korea University, Korea Mohamed Faouzi Atig, Uppsala University, Sweden Owolabi Legunsen, Cornell University, USA Pamela Zave, AT&T Laboratories, USA Pavel Panchekha, University of Utah, USA Rahul Gopinath, University of Sydney, Australia Rajiv Gupta, UC Riverside, USA Saman Amarasinghe, MIT, USA Santosh Pande, Georgia Institute of Technology, USA Sean Treichler, NVIDIA, USA Shachar Itzhaky, Technion, Israel Shaz Qadeer, Facebook, USA Sheng Chen, University of Louisiana at Lafayette, USA Shigeru Chiba, University of Tokyo, Japan Shriram Krishnamurthi, Brown University, USA Sreepathi Pai, University of Rochester, USA Stefan Brunthaler, University of the Federal Armed Forces in Munchen, Germany Steve Blackburn, Google, Australia Subhajit Roy, IIT Kanpur, India Sukyoung Ryu, KAIST, Korea Swarnendu Biswas, IIT Kanpur, India Thanh Vu Nguyen, George Mason University, USA Tiark Rompf, Purdue, USA Tien Nguyen, University of Texas at Dallas, USA Tomas Petricek, Charles University, Czech Republic Umut Acar, CMU, USA Wei Le, Iowa State, USA Wei Zhang , Meta, USA Xiaokang Qiu, Purdue University, USA Yingfei Xiong, Peking University, China Yizhou Zhang, University of Waterloo, Canada Youyou Cong, Tokyo Institute of Technology, Japan Yu David Liu, Binghamton, USA Yu Feng, UCSB, USA Yuepeng Wang, Simon Fraser University, Canada ##### Artifact Evaluation Committee Artifact Evaluation Committee Chairs: Guillaume Baudart, Inria - École normale supérieure, France Sankha Narayan Guria, University of Kansas, USA

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heterogeneous container smart constructor question
by Zoran Bošnjak 05 Sep '23

05 Sep '23

Dear haskellers, I am trying to add some type safety to the program in the following situation: There are some distinct 'Item t' types which come in groups. That is: 'EList' container can contain either: - items 0,1 - items 0,1,2,3 - items 0,1,2,3,4,5,6 All other combinations (like items 0,1,2) are invalid and shall be rejected by compiler. The 'EList' implementation (see below) seems to have this property. In addition, I would like to define a smart constructor (mkEList), to simplify EList construction from some linear (no groups) IList type. In other words, mkEList shall slice IList to proper groups. I am aware that I need to use a type class / type families for this. I have tried several approaches, but ghc was not happy with any. What is the correct implementation of mkEList? Here is a sample code and the intended usage: -- (sample build-test.hs) import GHC.TypeLits data Item (t :: Nat) = Item -- List/group of items data IList (ts :: [Nat]) where INil :: IList '[] ICons :: Item t -> IList ts -> IList (t ': ts) nil :: IList '[] nil = INil infixr 5 &: (&:) :: Item t -> IList ts -> IList (t : ts) (&:) = ICons -- Extended list of groups data EList (ts :: [Nat]) (tss :: [[Nat]]) where EList :: IList ts1 -> Maybe (EList ts2 tss) -> EList ts1 (ts2 ': tss) instance Eq (EList ts tss) -- Manual test type T1 = '[0, 1] type T2 = '[ '[2, 3], '[4, 5, 6], '[] ] test1 :: EList T1 T2 test1 = EList (Item @0 &: Item @1 &: nil) Nothing test2 :: EList T1 T2 test2 = EList (Item @0 &: Item @1 &: nil) (Just (EList (Item @2 &: Item @3 &: nil) Nothing)) test3 :: EList T1 T2 test3 = EList (Item @0 &: Item @1 &: nil) (Just (EList (Item @2 &: Item @3 &: nil) (Just (EList (Item @4 &: Item @5 &: Item @6 &: nil) Nothing)))) -- Intended usage -- | Helper function or class method :: IList ? -> EList ? ? mkEList :: a mkEList = undefined el1 :: EList T1 T2 el1 = mkEList ( Item @0 &: Item @1 &: nil) el2 :: EList T1 T2 el2 = mkEList ( Item @0 &: Item @1 &: Item @2 &: Item @3 &: nil) el3 :: EList T1 T2 el3 = mkEList ( Item @0 &: Item @1 &: Item @2 &: Item @3 &: Item @4 &: Item @5 &: Item @6 &: nil) check :: Bool -- expecting True check = and [el1 == test1, el2 == test2, el3 == test3] -- (end of sample) regards, Zoran

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The Haskell Foundation is seeking a new Executive Director
by David Christiansen 05 Sep '23

05 Sep '23

Dear Cafe, I just realized that we didn't yet post this here - apologies! I'll be stopping as ED of the Haskell Foundation at the end of the month, because I got an offer to go back to software development and work on a combination of technologies that I personally find extremely interesting (dependent types, procedural hygienic macros, language embedding, software verification, documentation and tools). It wasn't an easy decision to make, but I won't be disappearing from the world of pure functional programming. This means we need a new ED! You can see details here: https://haskell.foundation/careers/executive-director.html Every application received by the 29th will receive full consideration, but the board will continue taking applications until the new ED has been found. Until 22 September, I have time reserved to meet with people who are interested, but unsure about whether the role is a good fit. I myself have had these concerns - it was my first job not doing research or software development since I was 23 years old, after all. I'm happy to have an honest discussion about the job, how I did it, how someone else with different strengths might do it, what my daily life is like and the constraints that give rise to that, and so forth. Just let me know if you're interested. My canonical farewell post is here: https://discourse.haskell.org/t/an-opportunity-that-i-couldnt-pass-up/7485 Thanks for your support! I'll see you around. David

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