- Haskell-Cafe - Haskell.org

Model beverage
by Olaf Klinke 03 Apr '22

03 Apr '22

> Hi List, > > I came to Haskell from Java. At the beginning I was trying to map > traditional notions of mainstream languages onto the FP world as “How to > replace inheritance and late binding?”, etc. > > If Java developers drink coffee, then what is the model beverage for > haskellers? > > “Psyllium Husk” fits the role, because besides phonetic similarities, the > beverage is lazy (the recipe is simple - mix powder with water) and > immutable (goes through the intestinal tract largely unaltered). Plus it is > far off mainstream. > > > -- > > Best regards, > Daniil Iaitskov Absinthe comes to mind. It is very potent, popular among philosophersbut drives you crazy if consumed regularly, in large quantities. Cheers, Olaf

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Can't use TypeApplications with polymorphic let bind
by Georgi Lyubenov 29 Mar '22

29 Mar '22

Dear Cafe, I recently came upon this little "type-inference puzzle". Can anyone shine some light on why the third example doesn't compile? ``` {-# LANGUAGE TypeApplications #-} -- doesn't work -- I expect this, not sure why it happens {- class C m where c :: () -> m instance C Int where c () = 0 instance C Bool where c () = False f :: (Int, Bool) f = let x = c in (x (), x ()) -} -- works -- I expect this, not sure why it happens {- class C m where c :: () -> m instance C Int where c () = 0 instance C Bool where c () = False f :: (Int, Bool) f = let x u = c u in (x (), x ()) -} -- doesn't work -- I don't expect this, not sure why it happens {- class C m where c :: () -> m instance C Int where c () = 0 instance C Bool where c () = False f :: (Int, Bool) f = let x u = c u in (x @Int (), x @Bool ()) -- wtf.hs:54:5: error: -- • Cannot apply expression of type ‘() -> m0’ -- to a visible type argument ‘Int’ -- • In the expression: x @Int () -- In the expression: (x @Int (), x @Bool ()) -- In the expression: let x u = c u in (x @Int (), x @Bool ()) -- | -- 54 | (x @Int (), x @Bool ()) -- | ^^^^^^^^^ -} ``` Cheers, Georgi

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New Executive Director for the Haskell Foundation
by Richard Eisenberg 29 Mar '22

29 Mar '22

Official announcement on Discourse: https://discourse.haskell.org/t/new-executive-director-for-the-haskell-foun… <https://discourse.haskell.org/t/new-executive-director-for-the-haskell-foun…> Text repeated here (but responses from David and Andrew are already on Discourse): It is my great pleasure to announce the next Executive Director of the Haskell Foundation: David Thrane Christiansen. David is a long-time Haskeller who comes with a demonstrated passion for functional programming, having done intensive work with Idris, Racket, and Haskell, among other formative experiences. In particular, David was a key part of the Idris community when it morphed from a smallish language project to one more widely used. David holds a PhD in Computer Science from the IT University of Copenhagen (the city where he currently lives), has co-authored a book on dependent types (The Little Typer), and has worked for Galois and Deon Digital. Lest anyone get worried about one PhD excited about dependent types (me) involved in hiring another PhD excited about dependent types (David): over the course of many conversations about the HF, David has impressed upon me the importance of reaching out beyond current Haskell communities, seeking new voices and approaches. Haskell is a language that anyone can master -- but we have work to do to have its perception match that reality. I know David is committed to that course of action, and of focusing on the practical aspects of Haskell use that affect the Haskell community broadly. David begins his employment with the HF on Monday, May 2. About the process: The HF formed a Transition Committee (our charter is public: https://gitlab.haskell.org/hf/meta/-/blob/main/committees/transition.md) comprising José Pedro Magalhães (chair), Ed Kmett, and myself. We put together a call for applications and processed these applications as they came in. Applicants that passed an initial screening interview were given four additional interviews. The Transition Committee then made a recommendation to the Board based on the written feedback from these interviews, and the Board voted unanimously and enthusiastically to accept the recommendation to hire David. I hope you join me in being excited about this next chapter for the Haskell Foundation! Richard

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First CfP: FMBC 2022 - 4th International Workshop on Formal Methods for Blockchains
by Zaynah Dargaye 29 Mar '22

29 Mar '22

FMBC 2022 First Call for Papers [ Please distribute, apologies for multiple postings. ] ======================================================================== 4th International Workshop on Formal Methods for Blockchains (FMBC) - First Call https://fmbc.gitlab.io/2022 August 11, 2022, Haifa, Israel Co-located with the The Federated Logic Conference 2022 (FLoC 22 -- https://www.floc2022.org/) as a satellite workshop of the 34th International Conference on Computer-Aided Verification (CAV 2022 -- http://i-cav.org/2022/) ----------------------------------------------------------------- Important dates --------------------- Abstract submission: May 3, 2022 Full paper submission: May 10, 2022 Notification: June 15, 2022 Camera-ready: July 13, 2022 Workshop: August 11, 2022 Deadlines are Anywhere on Earth -- https://en.wikipedia.org/wiki/Anywhere_on_Earth. ---------------------- ---------------------- TOPICS OF INTEREST --------------------- Blockchains are decentralized transactional ledgers that rely on cryptographic hash functions for guaranteeing the integrity of the stored data. Participants on the network reach agreement on what valid transactions are through consensus algorithms. Blockchains may also provide support for Smart Contracts. Smart Contracts are scripts of an ad-hoc programming language that are stored in the Blockchain and that run on the network. They can interact with the ledger’s data and update its state. These scripts can express the logic of possibly complex contracts between users of the Blockchain. Thus, Smart Contracts can facilitate the economic activity of Blockchain participants. With the emergence and increasing popularity of cryptocurrencies such as Bitcoin and Ethereum, it is now of utmost importance to have strong guarantees of the behavior of Blockchain software. These guarantees can be brought by using Formal Methods. Indeed, Blockchain software encompasses many topics of computer science where using Formal Methods techniques and tools are relevant: consensus algorithms to ensure the liveness and the security of the data on the chain, programming languages specifically designed to write Smart Contracts, cryptographic protocols, such as zero-knowledge proofs, used to ensure privacy, etc. This workshop is a forum to identify theoretical and practical approaches of formal methods for Blockchain technology. Topics include, but are not limited to: * Formal models of Blockchain applications or concepts * Formal methods for consensus protocols * Formal methods for Blockchain-specific cryptographic primitives or protocols * Design and implementation of Smart Contract languages * Verification of Smart Contracts ---------------------- ---------------------- SUBMISSION --------------------- Submit original manuscripts (not published or considered elsewhere) with a page limit of 12 pages for full papers and Systematization of Knowledge (SoK) papers, 6 pages for short papers, and 2 pages for tool papers (excluding bibliography and short appendix of up to 5 additional pages). Alternatively, you may also submit an extended abstract of up to 3 pages (including a bibliography) summarizing your ongoing work in the area of formal methods and blockchain. Authors of selected extended abstracts are invited to give a short lightning talk. -------------------- -------------------- PROCEEDINGS ------------------- All submissions will be peer-reviewed by at least three members of the program committee for quality and relevance. Accepted regular papers (full and short papers) will be included in the workshop proceedings. ---------------------- ---------------------- INVITED SPEAKER --------------------- Massimo Bartoletti, Professor, Università degli Studi di Cagliari, Italy ---------------------- ---------------------- PROGRAM COMMITTEE --------------------- PC CO-CHAIRS * Zaynah Dargaye (Nomadic Labs, France) (zaynah.dargaye(a)nomadic-labs.com) * Schneidewind Clara, (MPI-SP, Germany) (clara.schneidewind(a)mpi-sp.org) PC MEMBERS Wolfgang Ahrendt (Chalmers University of Technology, Sweden) Leonardo Alt (Ethereum Foundation, Germany) Lacramioara Astefanoaei (Nomadic Labs, France) Roberto Blanco (MPI-SP, Germany) Joachim Breitner (Germany) Achim Brucker (University of Exeter, UK) Ethan Cecchetti (University of Maryland, USA) Manuel Chakravarty (IOHK & Tweag, Netherlands) Jing Chen (Algorand Inc, USA) Jérémie Decouchant (TU Delft, Netherlands) Antonella Del Pozzo (Université Paris-Saclay & CEA & List, France) Dana Drachsler Cohen (Technion, Israel) Cezara Dragoi (INRIA & ENS & CNRS & PSL, France) Ansgar Fehnker (Twente, Netherlands) Dominik Harz (Interlay & Imperial College London, UK) Lars Hupel (INNOQ, Germany) Igor Konnov (Informal Systems, Austria) Paul Laforgue (Nomadic Labs, France) Julian Nagele (Bank of America, USA) Russel O’Connor (Blockstream) Maria Potop-Butucaru (LIP6, France) Albert Rubio (Complutense University of Madrid, Spain) César Sanchez (IMDEA, Spain) Sun Meng (Peking University, China) Simon Thompson (IO Global, UK) Josef Widder (Informal Systems, Austria)

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[ANN] base16-0.3.2.0, base32-0.2.2.0, base64-0.4.2.4
by Emily Pillmore 28 Mar '22

28 Mar '22

Hello All, I'm pleased to announce that `base16`, `base32`, and `base64` have been updated to support GHC 9.2.x. In the most recent versions, due to GHC issue #20338 in which `targetByteOrder` was incorrect on Big Endian architectures, the required GHC version lower bound has been upped to GHC 8.10.x. In this version, GHC 8.10.x was silently patched to fix this behavior. Cheers, Emily

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inference with implicitparams seems broken
by rowan goemans 28 Mar '22

28 Mar '22

Hello everyone, I wonder why the following taken from an stackoverflow answer doesn't work: https://stackoverflow.com/questions/71184922/is-it-possible-to-infer-a-type…. Code of the answer posted here verbatim: ``` {-# LANGUAGE ImplicitParams #-} {-# LANGUAGE RankNTypes #-} module Temp where withX :: Int -> ((?x :: Int) => r) -> r withX x r = let ?x = x in r somethingThanNeedsX :: (?x :: Int) => Int somethingThanNeedsX = ?x + 2 foo :: Int foo = bar where bar = withX 42 baz baz = somethingThanNeedsX ``` This won't compile with the error message: ``` Orig.hs:19:11: error: • Unbound implicit parameter (?x::Int) arising from a use of ‘somethingThanNeedsX’ • In the expression: somethingThanNeedsX In an equation for ‘baz’: baz = somethingThanNeedsX In an equation for ‘foo’: foo = bar where bar = withX 42 baz baz = somethingThanNeedsX | 19 | baz = somethingThanNeedsX ``` If you give `baz` a type signature which includes the implicit param it compiles. But I think this is a bug. GHC should not require a type signature here. I tried searching for a GHC ticket but I couldn't find one. But that might also be down to me not using the right query. Anyway my question is, is this expected behavior? This really makes implicit params less ergonomic. Best regards, Rowan Goemans

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Munich Haskell Meeting, 2022-03-30 @ 19:30
by Leah Neukirchen 27 Mar '22

27 Mar '22

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Wednesday, March 30 at **Augustiner-Gaststätte Rumpler** at 19h30 CEST. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-mar-2022/ Everybody is welcome! Local COVID rules apply. cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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Hatlab: My attempt to make a library inspired by Matlab and NumPy
by TeraTux 27 Mar '22

27 Mar '22

Greetings! I made a library which implements functions similar to those in Matlab or NumPy. The code is not much clean yet, you can see it at https://gitlab.com/Hume2/hatlab . The functions with comments are intended to be used. I want to know if it is a good start or I just wasted time. The matrices can have arbitrary dimensions, starting from 0D matrices, which are basically scalars. Operations like + - * / are element-wise. I also implemented broadcasting of these operations. I also implemented indexing. Some examples: a = matrix2D [[1,2,3],[4,5,6],[7,8,9]] a !# [2,2] -- element at index [2,2] a !$ [At 1, All] -- 1st row a !$ [To (-1), All] -- all rows except the last one a !$ [Where $ a ># 5] -- all elements bigger than 5 (The ># operator returns a matrix of bools, I will come to that later.) It is also possible to update a matrix. These operations do not copy all the elements from the original matrix, they just make another matrix which points to the original matrix at places where it was not changed. Some examples: a = eye 5 b = matrix2D [[1,2,3],[4,5,6],[7,8,9]] a !:[FromTo 1 4, FromTo 1 4]:= b -- replace the middle square by a different matrix a !:[FromTo 1 4, FromTo 1 4]:= 1 -- set all values in the middle square to 1 a !:[FromTo 1 4, FromTo 1 4]:+= 1 -- add one to all values in the middle square a !:[FromTo 1 4, FromTo 1 4]:$= cos -- replace all values in the middle square by their cosine Operators are broadcasted the same way as in Matlab or NumPy. If one operand has size 1 and the other one has size N or vice-versa in given dimension, the operator acts as if the thinner matrix was repeated in the given dimension N times. Example: a = matrix1D [10, 20, 30] -- row vector b = matrix2D [[1], [2], [3]] -- column vector a + b -- returns [[11, 21, 31], [12, 22, 32], [13, 23, 33]] There is a function "scalar" which creates a 0D matrix out of any value, so we can do: a + (scalar 5) -- returns [15, 25, 35] a * (scalar 2) -- returns [20, 40, 60] If a type is in the class Num, Fractional or Floating, the matrix of the given type is also in the given class. Conversions are performed using the function "scalar", so we can write: a + 5 a * 2 because the "5" and "2" are then interpreted as 0D matrices. Operator * is interpreted as element-wise multiplication. To do matrix multiplication, use the × operator. It can be also used to multiply matrices with vectors. Examples: v = matrix1D [1,2,3] m = matrix2D [[1,0,1],[2,-1,1],[0,1,-1]] v × m -- multiply row vector v with matrix m m × v -- multiply matrix m with column vector v m × m -- multiply matrix m by itself There are also functions for element-wise boolean operations. They work similarly and they have the # suffix. Examples: a = matrix2D [[True, True], [False, False]] b = matrix2D [[True, False], [True, False]] a &# b -- element-wise and a |# b -- element-wise or There are also element-wise comparison functions in a similar fashion. Examples: a = eye 3 b = ones [3,3] a ==# b -- returns a matrix of bools saying where the element of matrix a is equal to the corresponding element in matrix b. a <# b -- similar as above except that it tests for being less than instead of equality. a ==# 1 -- Broadcasting works for these operators too, so this syntax is valid also. There are also other functions not described in this mail. I will not describe them here because this mail is already too long. Don't worry asking me if you don't understand the meaning of any function from my comments. I did not implement any algorithms for linear equation solving, not even any other matrix algorithms yet. If this library has any potential, I may do that in the future. Please, let me know if this library has any potential or it was just a waste of time. Hume2

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Haskell Symposium 2022: Call for Papers
by Nadia Polikarpova 26 Mar '22

26 Mar '22

========================================================================= ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2022 Ljubljana, Slovenia Thu 15 -- Fri 16 September, 2022 http://www.haskell.org/haskell-symposium/2022/ ========================================================================= The ACM SIGPLAN Haskell Symposium 2022 will be co-located with the 2022 International Conference on Functional Programming (ICFP). Differently from previous years, Haskell'22 will use a single-track submission process (that is, we will only have the regular track and no early track). The Haskell Symposium presents original research on Haskell, discusses practical experience and future development of the language, and promotes other forms of declarative programming. Topics of interest include: * Language design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts; * Tutorials, to document how to use a particular language feature, programming technique, tool or library within the Haskell ecosystem; * System Demonstrations, based on running software rather than novel research results. Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. Experience reports and functional pearls need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementers, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. Like an experience report and a functional pearl, tutorials should make a contribution from which other Haskellers can benefit. What distinguishes a tutorial is that its focus is on explaining an aspect of the Haskell language and/or ecosystem in a way that is generally useful to a Haskell audience. Tutorials for many such topics can be found online; the distinction here is that by writing it up for formal review it will be vetted by experts and formally published. System demonstrations should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. If your contribution is not a research paper, please mark the title of your experience report, functional pearl, tutorial or system demonstration as such, by supplying a subtitle (Experience Report, Functional Pearl, Tutorial Paper, System Demonstration). Submission Details ================== Formatting ---------- Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines. Authors should use the `acmart` format, with the `sigplan` sub-format for ACM proceedings. For details, see: http://www.sigplan.org/Resources/Author/#acmart-format It is recommended to use the `review` option when submitting a paper; this option enables line numbers for easy reference in reviews. Functional pearls, experience reports, tutorials and demo proposals should be labelled clearly as such. Lightweight Double-blind Reviewing ---------------------------------- Haskell Symposium 2022 will use a lightweight double-blind reviewing process. To facilitate this, submitted papers must adhere to two rules: 1. Author names and institutions must be omitted, and 2. References to authors' own related work should be in the third person (e.g., not "We build on our previous work" but rather "We build on the work of "). The purpose of this process is to help the reviewers come to an initial judgment about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. A reviewer will learn the identity of the author(s) of a paper after a review is submitted. Page Limits ----------- The length of submissions should not exceed the following limits: Regular paper: 12 pages Functional pearl: 12 pages Tutorial: 12 pages Experience report: 6 pages Demo proposal: 2 pages There is no requirement that all pages are used. For example, a functional pearl may be much shorter than 12 pages. In all cases, the list of references is not counted against these page limits. Deadlines --------- Abstract submission: 27 May 2022 (Fri) Paper submission: 3 June 2022 (Fri) Notification: 1 July 2022 (Fri) Deadlines are anywhere on Earth. Submission ---------- Submissions must adhere to SIGPLAN's republication policy (http://sigplan.org/Resources/Policies/Republication/) and authors should be aware of ACM's policies on plagiarism (https://www.acm.org/publications/policies/plagiarism) Program Committee members are allowed to submit papers, but their papers will be held to a higher standard. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. Papers should be submitted through HotCRP at: https://haskell22.hotcrp.com/ Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Supplementary material: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. This supplementary material should not be submitted as part of the main document; instead, it should be uploaded as a separate PDF document or tarball. Supplementary material should be uploaded at submission time, not by providing a URL in the paper that points to an external repository. Authors can distinguish between anonymized and non-anonymized supplementary material. Anonymized supplementary material will be visible to reviewers immediately; non-anonymized supplementary material will be revealed to reviewers only after they have submitted their review of the paper and learned the identity of the author(s). Resubmitted Papers: authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the conference chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. Proceedings =========== Accepted papers will be included in the ACM Digital Library. Their authors will be required to choose one of the following options: - Author retains copyright of the work and grants ACM a non-exclusive permission-to-publish license (and, optionally, licenses the work with a Creative Commons license); - Author retains copyright of the work and grants ACM an exclusive permission-to-publish license; - Author transfers copyright of the work to ACM. For more information, please see ACM Copyright Policy (http://www.acm.org/publications/policies/copyright-policy) and ACM Author Rights (http://authors.acm.org/main.html) Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. Publication date: The official publication date of accepted papers 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. Artifacts ========= Authors of accepted papers are encouraged to make auxiliary material (artifacts like source code, test data, etc.) available with their paper. They can opt to have these artifacts published alongside their paper in the ACM Digital Library (copyright of artifacts remains with the authors). If an accepted paper's artifacts are made permanently available for retrieval in a publicly accessible archival repository like the ACM Digital Library, that paper qualifies for an Artifacts Available badge (https://www.acm.org/publications/policies/artifact-review-badging#available) Applications for such a badge can be made after paper acceptance and will be reviewed by the PC chair. Program Committee ================= Lennart Augustsson Epic Games Jean-Philippe Bernardy University of Gothenburg Iavor Diatchki Galois, Inc Michael Gale Tweag William Hallahan Yale University Makoto Hamana Gumma University John Hughes Chalmers University of Technology Alexis King Tweag James Koppel Massachusets Institute of Technology Rudy Matela Dominic Orchard University of Kent Nadia Polikarpova (chair) University of California, San Diego Eric Seidel Bridgewater Associates Satnam Singh Groq Wouter Swierstra Utrecht University Hiroshi Unno University of Tsukuba Marco Vassena CISPA - Helmholtz-Zentrum Dimitrios Vytiniotis DeepMind If you have questions, please contact the chair at: npolikarpova(a)ucsd.edu =========================================================================

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Accessing a MinGW/MSYS2 shell from Setup.hs
by Hécate 26 Mar '22

26 Mar '22

Hi everyone, I am writing a custom Setup.hs to do an Autotools build for a bundled library. This is easy everywhere with `process` _except_ Windows, because I can't get a shell with the Autotools in them, despite there definitely being one. `process` gives me a cmd.exe shell, which wouldn't know about the Autotools, and on Windows, _any_ GHC installation has to have certain POSIX stuff available, which is why it bundles MinGW. Is the shell I get from that accessible from Setup.hs, via `process` or otherwise? Cheers, Hécate -- Hécate ✨ 🐦: @TechnoEmpress IRC: Hecate WWW:https://glitchbra.in RUN: BSD

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