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Re: [Haskell-cafe] Better names for
by Olaf Klinke 24 Apr '20

24 Apr '20

> > fmap f. If I could re-define Haskell from scratch, I'd probably > >name > > the Functor type class function 'map' > > As it was in Haskell 1.4 That's interesting, I did not know this. Thanks for sharing. Are there any public records as to why the decision was made to re-name 'map' to 'fmap'? I can not find any mention in the Haskell98 report(s). There is a stackoverflow thread (#6824255) which mentions paedagogical reasons, simplifying error messages. I sometimes use the current naming 'map' to specialize a polymorphic function to work exclusively on lists where any functor could have been used. Other than that, I can not quite see the use in keeping 'map' around when it is equivalent to fmap. What reasons are there apart from backwards compatibility? Are there re-write rules that make 'map's (operational) semantics different to 'fmap'? Olaf

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Does GHC recognise that CmpSymbol s1 s2 ~ EQ implies s1 ~ s2 ?
by Evgeny Permyakov 24 Apr '20

24 Apr '20

By semantic CmpSymbol s1 s2 ~ EQ should be equivalent to s1 ~ s2 for s1 , s2 :: Symbol Does GHC recognize it? If not, is there some trick to obtain evidence of the second constraint from the first ? I'm talking about context of type class instance declarations.

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Re: [Haskell-cafe] Better names for
by Olaf Klinke 23 Apr '20

23 Apr '20

> I've heard several times that some Haskell type classes and methods > are > ill-named. > > For instance, a functor can be both covariant and contravariant, > while > Haskell `Functor` typeclass i just covariant. Would `Cofunctor` be a > better name for it? And what about the `fmap` method? Would it be > better > to call it `comap`? How about `Bifunctor`, `Profunctor` and others? Hi Marc, part of the answer is: For historical reasons and to preserve backwards compatibility. The term "Functor", however, comes from category theory. MacLane [1] defines the term "Functor" to refer to covariant functors. The notion of "contravariant" is introduced via the concept of "opposite category" [2] which has the same objects but direction of arrows reversed. Thus a contravariant functor F: C -> D is just an ordinary functor C -> D^op. Category theory has no name for the action of a functor on arrows, Haskell had to make up a name, which ended up to be "fmap". Sometimes the notation F(f) is used in category theory where in Haskell we write fmap f. If I could re-define Haskell from scratch, I'd probably name the Functor type class function 'map' and omit the map function on lists, since it is the same as the Functor instance. As for your suggestion of 'comap': The prefix co- in category theory is mostly used in conjunction with the opposite construction [3], whence a category theorist would believe 'comap' to mean the opposite of 'map'. Regards, Olaf [1] Saunders MacLane: Categories for the Working Mathematician. ISBN 7- 5062-6008-5 [2] See Op in Data.Functor.Contravariant [3] See categorical concepts like limit vs. colimit, cone vs. cocone.

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Better names for
by Marc Busqué 22 Apr '20

22 Apr '20

Hi there! I've heard several times that some Haskell type classes and methods are ill-named. For instance, a functor can be both covariant and contravariant, while Haskell `Functor` typeclass i just covariant. Would `Cofunctor` be a better name for it? And what about the `fmap` method? Would it be better to call it `comap`? How about `Bifunctor`, `Profunctor` and others? Thanks, Marc Busqué http://waiting-for-dev.github.io/about/

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Where is Show for GHC AST?
by Daneel Yaitskov 22 Apr '20

22 Apr '20

Hi, I am trying to modify LiquidHaskell and want to see how source code is represented in AST format. I think I have AST i.e. HsExpr value, but there is no Show instance for that. I noticed that GHC classes implement similar class Outputable, but it doesn't do what I expected. It just reconstruct AST back to source code. I could probably write a TH function generating Show instances for all types which HsExpr depends on, but I hope there is more straight forward way to do that. And after all I curious what is the reason for not having Show for GHC AST types? It would be so convenient having Show. -- Daneel S. Yaitskov Java Developer

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Re: [Haskell-cafe] Where is Show for GHC AST?
by Michal J Gajda 22 Apr '20

22 Apr '20

Hi Daneel, Did you check the `Outputable` class? http://hackage.haskell.org/package/ghc-8.6.5/docs/Outputable.html#t:Outputa… -- Cheers Michał

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FMBC 2020: 2nd Workshop on Formal Methods for Blockchains (CfP, Deadline Extension)
by Bruno Bernardo 21 Apr '20

21 Apr '20

[ Please distribute, apologies for multiple postings. ] ======================================================================== 2nd Workshop on Formal Methods for Blockchains (FMBC) 2020 - Second Call https://fmbc.gitlab.io/2020 July 19, 2020, Los Angeles, USA Co-located with the 32nd International Conference on Computer-Aided Verification (CAV 2020) http://i-cav.org/2020/ ------------------------------------------------------------- IMPORTANT DATES -------------------------------- Abstract submission: May 5, 2020 (extended) Full paper submission: May 12, 2020 (extended) Notification: June 16, 2020 (extended) Camera-ready: July 7, 2020 Conference: July 19, 2020 -------------------------------- -------------------------------- 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 maximum of twelve pages (full papers), six pages (short papers), and two pages (extended abstract) describing new and emerging ideas or summarizing existing work). Each paper should include a title and the name and affiliation of each author. Authors of selected extended-abstracts are invited to give a short lightning talk. At least one author of an accepted paper is expected to present the paper at the workshop as a registered participant. Submission link: https://easychair.org/conferences/?conf=fmbc2020 The authors are encouraged to use LaTeX and the EasyChair style files: https://easychair.org/publications/for_authors -------------------------------- -------------------------------- 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 -------------------------------- Grigore Rosu, Professor at University of Illinois at Urbana-Champaign, USA and Founder of Runtime Verification http://fsl.cs.illinois.edu/index.php/Grigore_Rosu https://runtimeverification.com/ -------------------------------- -------------------------------- PROGRAM COMMITTEE -------------------------------- PC CO-CHAIRS * Bruno Bernardo (Nomadic Labs, France) (bruno(a)nomadic-labs.com) * Diego Marmsoler (University of Exeter, UK) (D.Marmsoler(a)exeter.ac.uk) PC MEMBERS * Wolfgang Ahrendt (Chalmers University of Technology, Sweden) * Lacramioara Astefanoei (Nomadic Labs, France) * Massimo Bartoletti (University of Cagliari, Italy) * Bernhard Beckert (Karlsruhe Institute of Technology, Germany) * Achim Brucker (University of Exeter, UK) * Silvia Crafa (Universita di Padova, Italy) * Zaynah Dargaye (Nomadic Labs, France) * Jérémie Decouchant (University of Luxembourg, Luxembourg) * Ansgar Fehnker (University of Twente, Netherlands) * Georges Gonthier (Inria, France) * Florian Kammueller (Middlesex University London, UK) * Maurice Herlihy (Brown University, USA) * Igor Konnov (Informal, Austria) * Andreas Lochbihler (Digital Asset, Switzerland) * Anastasia Mavridou (NASA Ames, USA) * Simão Melo de Sousa (Universidade da Beira Interior, Portugal) * Andrew Miller (University of Illinois at Urbana-Champaign, USA) * Karl Palmskog (KTH, Sweden) * Vincent Rahli (University of Birmingham, UK) * Andreas Rossberg (Dfinity Foundation, Germany) * Claudio Russo (Dfinity Foundation, USA) * César Sanchez (Imdea, Spain) * Clara Schneidewind (TU Wien, Austria) * Ilya Sergey (Yale-NUS College/NUS, Singapore) * Bas Spitters (Aarhus University/Concordium, Denmark) * Mark Staples (CSIRO Data61, Australia) * Meng Sun (Peking University, China) * Simon Thompson (University of Kent, UK) * Philip Wadler (University of Edinburgh / IOHK, UK)

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[ANN] Haskell Beginners WT.Social Community: "Haskell: The Haskell-Beginners Community"
by Benjamin L. Russell 18 Apr '20

18 Apr '20

Twenty-eight days ago (on March 23, 2020 JST), I created a new Haskell beginners WT.Social community, "Haskell: The Haskell-Beginners Community" (see https://pashpost.com/group/haskell-the-haskell-beginners-community) and migrated a substantial portion of the posts originally from my former corresponding pashPOST (since renamed to "theTUNDRA") community of the same name thereto (sansposts with missing links or irrelevant content). Feel free to join and contribute! -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Computer Science Document Translator/Editor "Furuike ya, kawazu tobikomu mizu no oto." -- Matsuo Basho^

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GHC Dockerimage
by Alexander Ben Nasrallah 18 Apr '20

18 Apr '20

Hi fellow Haskellers, since I was missing a Dockerimage for GHC built with musl and integer-simple for static linking, which is kept up to date, I created my own. I use it to test compatibility with different GHC versions and provide a full statically linked binary for download with GitLab CI/CD. Maybe someone will find it useful, too. Or maybe there already is another more sophisticated project someone can point me to. https://registry.hub.docker.com/r/neosimsim/ghc

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Attoparsec: match many, skipping rest
by amindfv＠gmail.com 17 Apr '20

17 Apr '20

Say I've got an Attoparsec parser like: p = string "prio:" *> digit And some text, e.g. s = "this is just a prio:5 example, I'd prio:6 very much like to prio:4 parse" What's the most idiomatic way to apply p to s so that I get out a list ['5', '6', '4']? Thanks, Tom

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