- Haskell-Cafe - Haskell.org

Improvements to package hosting and security
by Michael Snoyman 03 May '15

03 May '15

Many of you saw the blog post Mathieu wrote[1] about having more composable community infrastructure, which in particular focused on improvements to Hackage. I've been discussing some of these ideas with both Mathieu and others in the community working on some similar thoughts. I've also separately spent some time speaking with Chris about package signing[2]. Through those discussions, it's become apparent to me that there are in fact two core pieces of functionality we're relying on Hackage for today: * A centralized location for accessing package metadata (i.e., the cabal files) and the package contents themselves (i.e., the sdist tarballs) * A central authority for deciding who is allowed to make releases of packages, and make revisions to cabal files In my opinion, fixing the first problem is in fact very straightforward to do today using existing tools. FP Complete already hosts a full Hackage mirror[3] backed by S3, for instance, and having the metadata mirrored to a Git repository as well is not a difficult technical challenge. This is the core of what Mathieu was proposing as far as composable infrastructure, corresponding to next actions 1 and 3 at the end of his blog post (step 2, modifying Hackage, is not a prerequesite). In my opinion, such a system would far surpass in usability, reliability, and extensibility our current infrastructure, and could be rolled out in a few days at most. However, that second point- the central authority- is the more interesting one. As it stands, our entire package ecosystem is placing a huge level of trust in Hackage, without any serious way to vet what's going on there. Attack vectors abound, e.g.: * Man in the middle attacks: as we are all painfully aware, cabal-install does not support HTTPS, so a MITM attack on downloads from Hackage is trivial * A breach of the Hackage Server codebase would allow anyone to upload nefarious code[4] * Any kind of system level vulnerability could allow an attacker to compromise the server in the same way Chris's package signing work addresses most of these vulnerabilities, by adding a layer of cryptographic signatures on top of Hackage as the central authority. I'd like to propose taking this a step further: removing Hackage as the central authority, and instead relying entirely on cryptographic signatures to release new packages. I wrote up a strawman proposal last week[5] which clearly needs work to be a realistic option. My question is: are people interested in moving forward on this? If there's no interest, and everyone is satisfied with continuing with the current Hackage-central-authority, then we can proceed with having reliable and secure services built around Hackage. But if others- like me- would like to see a more secure system built from the ground up, please say so and let's continue that conversation. [1] https://www.fpcomplete.com/blog/2015/03/composable-community-infrastructure [2] https://github.com/commercialhaskell/commercialhaskell/wiki/Package-signing… [3] https://www.fpcomplete.com/blog/2015/03/hackage-mirror [4] I don't think this is just a theoretical possibility for some point in the future. I have reported an easily trigerrable DoS attack on the current Hackage Server codebase, which has been unresolved for 1.5 months now [5] https://gist.github.com/snoyberg/732aa47a5dd3864051b9

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Re: [Haskell-cafe] Improvements to package hosting and security
by Mathieu Boespflug 03 May '15

03 May '15

Define "superior"? As argued in the proposal, the salient features are that by devolving practically everything to Git+GPG, we end up with less code to maintain in our tooling, less code to maintain in our infrastructure (namely hackage-server), a more reliable service, and a smaller chance of buggering up security related activities (such as signing and managing trust). We're not introducing dependencies on dynamically linked system libraries that makes tooling hard to distribute. We're not asking users to install anything new that isn't already a staple of most developer desktops, and not asking users, Hackage trustees and Hackage admins to manage new identities with new key formats that aren't the existing ones they already have (namely GnuPG). Further, users can still opt-out of signature verification if they want to. Compared to alternative approaches - there has been a proposal to get incremental updates à la Git differently by growing (potentially infinitely) the end of a tar file served by the server via HTTP. This means grabbing the history for new package revisions cannot be opted out from easily. With Git, you get this for free, since users can `git clone --depth=1` and still be able to do a `git pull` later and verify signatures. You further get the advantage of being able to directly mine the history of changes, using standard tools, something that can't be done directly on the tar file without more custom tooling (or post conversion to Git). On 28 April 2015 at 23:33, Bardur Arantsson <spam(a)scientician.net> wrote: > On 28-04-2015 23:09, Mathieu Boespflug wrote: > > [removing erroneous haskell-cafe(a)googlegroups.com from To list.] > > (I'm not the person you're responing to. From the mail-headers, I can't > see the person(s) you're responding to, but so be it.) > > Do you have evidence that your approach is superior, and could you > please cite it? [Or, alternatively provide negative evidence for > $OTHER_APPROACH.]) > > Regards, > > -- > You received this message because you are subscribed to the Google Groups > "Commercial Haskell" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to commercialhaskell%2Bunsubscribe(a)googlegroups.com. > To post to this group, send email to commercialhaskell(a)googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/commercialhaskell/mhouaf%24it2%241%40ger.… > . > For more options, visit https://groups.google.com/d/optout. >

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Meet some problem when installing Agda
by Zongzhe Yuan 03 May '15

03 May '15

Hi I want to use Agda on my computer and I follow the instruction http://wiki.portal.chalmers.se/agda/pmwiki.php?n=Main.MacOSX However when I was using cabal install Agda to install agda, the terminal said The program cpphs version >=1.18.6 && <1.19 is required but the version found at /Users/XXXXXX/Library/Haskell/bin/cpphs is version 1.19 Do you have some idea how could i fix that problem? Zongzhe Yuan This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system, you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Is it acceptable if Applicative behave not like a Monad
by Alexey Uimanov 02 May '15

02 May '15

Hello, I have such a question: assume you have some type `T` which has Applicative and Monad instances. Is it ok if code like this: foo :: Int -> T String bar :: Int -> T Int (,) <$> foo 10 <*> bar "20" behaves not like this code: foobar = do x <- foo 10 y <- bar "20" return (x, y) The word "behaves" I mean not just returning value but the effect performed also.

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PSA: How to use the cabal-version field in cabal files
by Adam Bergmark 02 May '15

02 May '15

The cabal-version field seems pretty mysterious. Recommendation: Set it no higher than >= 1.10, Cabal will warn you if it's too low. This field contains the format of the cabal file, the number corresponds to the Cabal release. Hence this version is incremented more often than the format actually changes. There have been no significant changes between 1.10 and 1.20. The Cabal source is surprisingly helpful as a changelog: https://github.com/haskell/cabal/blob/641e854ae663e2b34f34ecc11ba663ac3a9bd… By setting it too high you risk users getting errors like "The package 'foo' requires Cabal library version -any && >=1.14 but no suitable version is installed." This can be problematic for anyone using an older GHC or if there are Cabal releases outside of the GHC release cycle. You may get this error even if you have a newer Cabal if it doesn't ship with GHC. Happy hacking, Adam

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Import hiding module
by amindfv＠gmail.com 02 May '15

02 May '15

It's possible to write e.g. module A (module A.B, x) where To reexport everything from A.B And we can import A hiding (x) Is there a way to also import A hiding (module A.B) ? Thanks

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Swapping type arguments
by Alexey Uimanov 02 May '15

02 May '15

This question probably asked already. I have a type data T m b a = T (m (b, a)) and it should be instance of `Bifunctor` and `MonadTrans` same time. But there is a problem: instance Bifunctor (T m) is ok, but instance MonadTrans (T ... is not, because first argument is `m` but we need `b`. Type can be rewritten like data T b m a = T (m (b, a)) and instance of MonadTrans is ok: instance MonadTrans (T b) but how to define Bifunctor? instance Bifunctor (T ... I did not found how to workaround this. Is there any type magic for such cases?

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Haskell Weekly News
by Kim-Ee Yeoh 01 May '15

01 May '15

*Top Picks:* - Haskell wins a bumper crop of 18 accepted Google Summer of Code proposals <http://www.reddit.com/r/haskell/comments/342rvp/google_summer_of_code_18_pr…>. Mentor offers total 44, another thumpin' sign of life. Kudos to Edward Kmett, Johan Tibell, Shachaf Ben-Kiki, and Gershom Bazerman. Gloria Haskella sine labore nulla. - Reddit Haskell celebrates <http://www.reddit.com/r/haskell/comments/33wnf1/20k_rhaskell_subscribers_ni…> 20k subscribers. It's the 7th largest PL community on reddit <https://www.reddit.com/r/programming/wiki/faq#wiki_what_language_reddits_ar…> after python, javascript, java, php, ruby, c++, in that order. - Matthew Griffith <http://mechanical-elephant.com/thoughts/2015-04-20-becoming-productive-in-h…> migrates away from Python: "I do most of my web prototyping in Haskell now." A journey vividly logged and much loved on Hacker News <https://news.ycombinator.com/item?id=9431944>. And also on Proggit <http://www.reddit.com/r/programming/comments/33oyx9/becoming_productive_in_…> and Reddit Haskell <http://www.reddit.com/r/haskell/comments/33mnlc/becoming_productive_in_hask…> . - A web developer migrates away from Rails to Haskell and explains on HN the 10x advantage <https://news.ycombinator.com/item?id=9419601#up_9420448> he reaps. - Fancy Python in Haskell dress? Check out Dogelang <http://pyos.github.io/dg/>, charmingly defiant: "With Haskell's syntax but none of its type system, dg is the best way to make fans of static typing shut up already." Proggit kibbitzing here <http://www.reddit.com/r/programming/comments/33kleg/dg_its_a_python_no_its_…>, HN there <https://news.ycombinator.com/item?id=9432383>. - Caio Rordrigues copiously illustrates <https://github.com/caiorss/Functional-Programming> Haskell programming. Pretty: a tax bracket tool <https://github.com/caiorss/Functional-Programming#tax-brackets> and a coffee shop Point-of-Sale DSL <https://github.com/caiorss/Functional-Programming#small-dsl-domain-specific…>. It's almost a whole book! - Christian Marie starts the ball rolling on library cheatsheets <https://github.com/anchor/haskell-cheat-sheets/> to guide your way through the jungle of hackage. Moar, moar! <http://www.reddit.com/r/haskell/comments/33sc98/haskell_cheat_sheets_for_co…> - Got a C library you'd love Haskell bindings for? Remember Ian Ross and his new C2HS release <http://haskell.1045720.n5.nabble.com/Haskell-Weekly-News-td5768107.html>? Well, Ian's happy <http://haskell.1045720.n5.nabble.com/Tutorial-Ideas-td5808049.html> to do it for you. Provisos <http://www.skybluetrades.net/blog/posts/2015/04/27/c2hs-tutorial-request.ht…> apply. - Olle Fredriksson announces a combinator-based Earley parsing library <https://github.com/ollef/Earley> which accepts context-free but not context-sensitive (monadic parsing) grammars. Discussion <https://www.reddit.com/r/haskell/comments/33l9cr/ann_earley_parsing_library/> reveals that "one enormously important difference for this library is that it reports all possible parses." - Another Lennart, last name Spitzner, creates another genie that turns type signatures into programs. Unlike Djinn, Exference <http://haskell.1045720.n5.nabble.com/ANN-exference-a-different-djinn-td5807…> makes no promises over termination. "Your wish is my command even at the expense of closure." - Like Agda? You can now enjoy the hole-driven development style in Haskell, brought to you courtesy of Mote by Izaak Meckler <https://github.com/imeckler/mote>. Discussion here <https://www.reddit.com/r/haskell/comments/33v4nm/ann_mote_a_tool_bringing_h…> . <http://tomassetti.me/an-erd-web-server-generation-entity-diagrams-from-a-te…> - Federico Tomassetti <http://tomassetti.me/an-erd-web-server-generation-entity-diagrams-from-a-te…> creates a web-based interface to Andrew Gallant's erd tool <https://github.com/BurntSushi/erd>. Entity-Relationship Diagrams (ERD) come from the database world and help visualize {one,many} to {one,many} relationships. Federico's web app enables him to use erd everywhere without having to install the tool chain multiple times. - Mark Dominus gives a beginner spin <http://blog.plover.com/prog/haskell/monad-search.html> to the chestnut of SEND + MORE = MONEY <https://en.wikipedia.org/wiki/Verbal_arithmetic>. This puzzle site <http://programmingpraxis.com/2012/07/31/send-more-money-part-1/> has comparisons with other languages. - Got a number system? Flip it into a data structure <https://www.fpcomplete.com/user/edwardk/fibonacci/leonardo>. Re-flip it into an efficient search algorithm <https://www.fpcomplete.com/user/edwardk/fibonacci/search>. Edward Kmett shows you how. Respective discussion here <http://www.reddit.com/r/haskell/comments/342s31/edward_kmett_leonardo_rando…> and here <http://www.reddit.com/r/haskell/comments/346b6t/edward_kmett_openended_fibo…> . *In Memoriam* - A key founder of Haskell, Professor Paul Hudak, completed <http://yaledailynews.com/blog/2015/04/30/hudak-spirited-saybrugian-and-cs-p…> his end-of-life plan <http://www.caringbridge.org/visit/hudak/journal/view/id/5538f5cea589b4216c0…> after a five-year encounter with leukemia. He stays <https://news.ycombinator.com/item?id=9431017> in the thoughts <https://news.ycombinator.com/item?id=9465999> of all <http://www.reddit.com/r/haskell/comments/33oe4b/holding_on_and_letting_go/> who cherish <http://www.reddit.com/r/haskell/comments/34exz3/prof_hudak_passed_away_last…> his gifts <http://www.reddit.com/r/programming/comments/34f19q/paul_hudak_creator_of_h…> from the heart. *Quotes of the Week* - A type system flattens the cost of change curve <http://www.agilemodeling.com/essays/costOfChange.htm>. -- Chad Austin <http://chadaustin.me/2015/04/the-long-term-problem-with-dynamically-typed-l…> - The MLs and Haskell remind me of Brian Eno's line about how the first Velvet Underground album only sold 30,000 copies, but "everyone who bought one of those 30,000 copies started a band". -- Source <https://news.ycombinator.com/item?id=9431944#up_9437017> - On the value of Haskell <https://news.ycombinator.com/item?id=9445968#up_9448988>: I find I'm able to accomplish tasks which would otherwise be beyond my skill and intelligence. For example, even though C was the first language I learned, I can't imagine writing a parser in C after discovering the simplicity & readability of monadic parsing in Haskell. - Haskell's level of abstraction is so crazy that they can actually swap out their entire I/O system for another one without changing any application interfaces, this one blew my mind, it's the change that makes GHC 7.8 run the Warp webserver twice as fast. ... All of this without changing a line in Warp, they just transparently made every traditional Haskell use modern I/O principles. Academics man, they're smart ;) -- Source <https://news.ycombinator.com/item?id=9419601#up_9432564> - An old man loved is winter with flowers. -- Edgar Z. Friedenberg *Cool Beans of the Week* - Ravi Chugh and his fine team at U. Chicago just concluded stateside's first ever FRP-based FP course for undergrads using Elm. Check out the student projects <https://www.classes.cs.uchicago.edu/archive/2015/winter/22300-1/Showcase.ht…> for inspiration on FRP architecture. Over in Bonn, Janis Voigtländer also gave such a course <https://groups.google.com/d/msg/elm-discuss/Qjs6sp3lZq0/8aa5bvYcdDYJ> that completed this year. Paul's legacy lives on. p.s. Coming soon: Cabal Hell -- Kim-Ee

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[TFP'15] call for participation
by Peter Achten 01 May '15

01 May '15

----------------------------- L A S T C A L L F O R P A R T I C I P A T I O N ----------------------------- ======== TFP 2015 =========== 16th Symposium on Trends in Functional Programming June 3-5, 2015 Inria Sophia Antipolis, France http://tfp2015.inria.fr/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. The selected revised papers will be published as a Springer Lecture Notes in Computer Science (www.springer.com/lncs) volume. TFP 2015 will be the main event of a pair of functional programming events. TFP 2015 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 2nd. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * and in Soesterberg (The Netherlands) in 2014. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == INVITED SPEAKERS == TFP is pleased to announce talks by the following two invited speakers: * Laurence Rideau is a researcher at INRIA and is interested in the semantics of programming languages , the formal methods, and the verification tools for programs and mathematical proofs. She participated in the beginnings of the Compcert project (certified compiler), and is part of the Component Mathematical team in the MSR-INRIA joint laboratory, who performed the formalization of the Feit-Thompson theorem successfully. Thirty years ago, computers barged in mathematics with the famous proof of the Four Color Theorem. Initially limited to simple calculation, their role is now expanding to the reasoning whose complexity is beyond the capabilities of most humans, as the proof of the classification of finite simple groups. We present our large collaborative adventure around the formalization of the Feit-Thompson theorem (http://en.wikipedia.org/wiki/Feit%E2%80%93Thompson_theorem) that is a first step to the classification of finite groups and that uses a palette of methods and techniques that range from formal logic to software (and mathematics) engineering. * Anil Madhavapeddy == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2015 program chair, Manuel Serrano. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == SPONSORS == TFP is financially supported by Erlang Solutions. == PROGRAM == Please find the program at: http://tfp2015.inria.fr/program/ The program features two invited talks by Laurence Rideau and Anil Madhavapeddy and one comprehensive Dart tutorial by Florian Loitsch. == IMPORTANT DATES == Registration: May 4, 2015 TFP Symposium: June 3-5, 2015 == PROGRAM COMMITTEE == Janis Voigtländer University of Bonn, DE Scott Owens University of Kent, UK Neil Sculthorpe Swansea University, UK Colin Runciman University of York, UK Manuel Serrano Inria (PC chair), FR Rinus Plasmeijer University of Nijmegen, NL Tomas Petricek University of Cambridge, UK Marco T. Morazan Seton Hall University, USA Wolfgang De Meuter Vrije Universiteit Brussel, BE Michel Mauny Ensta ParisTech, FR Sam Lindley The University of Edinburgh, UK Daan Leijen Microsoft, USA Jurriaan Hage Utrecht University, NL Andy Gill University of Kansas, USA Thomas Gazagnaire University of Cambrige, UK Lars-Ake Fredlund Universidad Politécnica de Madrid, ES Jean-Christophe Filliatre Université Paris Sud Orsay, FR Marc Feeley Université de Montréal, CA Olaf Chitil University of Kent, UK Edwin Brady University of St Andrews, UK

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Roles, GND, Data.Coerce
by David Terei 01 May '15

01 May '15

All, An issue that came up with GHC 7.8 was the design of Roles and Data.Coerce, with it's ability to break module abstractions by default, requiring programmers adopt explicit role annotations to enforce some types of invariants for abstract data types. Because of this issue, as of now, GND & Data.Coerce are still disabled in Safe Haskell. We'd like to change this but need feedback from everyone. I've written up a wiki page with lots of information on the issue: https://ghc.haskell.org/trac/ghc/wiki/SafeRoles Please read, it has information on how Roles work, the problem it raises and subtleties in the current system. Possible paths forward are also there, but I'll include below. Please be aware that this discussion is about Roles in general, not specifically how when using -XSafe. Ideally we'd come up with a solution that works regardless of if using Safe Haskell or not. I personally like option (3), although it isn't clear to me how hairy the implementation would be. == Possible Paths Forward for Roles == 1) Do Nothing -- Keep Roles & GND unchanged, keep them unsafe in Safe Haskell. 2) Accept as Safe -- Keep Roles & GND unchanged, accept them as safe in Safe Haskell and warn users that they neednominal role annotations on ADTs. 3) In-scope constructor restriction for lifting instances -- The newtype constructor restriction for unwrapping instances could be extended to both data types, and the lifting instances of Data.Coerce. This is, GND & Coercing under a type constructor is allowed if (a) all involved constructors are in scope, or (b) the constructors involved have been explicitly declared to allow coercion without them being in scope. I.e., (b) allows library authors to opt-into the current GHC behavior. This would require new syntax, probably just an explicit deriving Coercible statement. 4) Change default role to nominal -- This will prioritize safety over GND, and the belief is that it may break a lot of code. Worse, that it will be an ongoing tax as role annotations will be needed to enable GND. 5) Nominal default when constructors aren't exported -- When a module doesn't export all the constructors of a data type, then the type parameters of the data type should default to nominal. This heuristic seems to capture somewhat the intention of the user, but given the practice of defining an Internal module that exports everything, it seems of limited use. 6) Nominal default in future -- Add a new extension, SafeNewtypeDeriving that switches the default role to nominal, but continue to provide a deprecated GND extension to help with the transition. The claims in support of representational roles as default though believe that nominal by default has an ongoing, continuous tax, not just a transition cost. So it isn't clear that any scheme like this satisfies that argument. 7) Safe Haskell Specific -- Many of the above approaches could be adopted in a Safe Haskell specific manner. This isn't ideal as it makes safe-inference harder and Safe Haskell less likely to remain viable going forward. Richard suggests one such idea. == The belief by many people seems to be that (4) and (6) would be too much of burden. I'd like to avoid (7) if possible. It isn't clear to me if (7) ends up better than (2). I'm going to try to setup some infastructure for compiling Hackage so that we can measure how impactful these changes would be. Cheers, David

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