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Munich Haskell Meeting, 2018-02-27 @ 19:30
by Christian Neukirchen 25 Feb '18

25 Feb '18

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Tuesday, Feburary 27, this time at Schiller Bräu (Schillerstr. 23) at 19h30. 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-feb-2018/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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How to control emitting other-modules with hpack
by 姓名 25 Feb '18

25 Feb '18

Hi there, I don't want to refer some (test) files defined at other-modules section but hpack emits that automatically. How can I control that emitting from package.yaml?

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HsOpenSSL doesn't build
by fr33domlover 25 Feb '18

25 Feb '18

Hello Haskellers, For a long time I did my Haskell coding on a laptop running Trisquel 7 GNU/Linux, 64-bit. I had stack installed from FPComplete's debian repo, and GHC 7.10.3 installed from hvr's PPA. I was working, among other things, on a program that I built last time with LTS 6.5 and everything was okay. Then I moved to a new laptop, now I run Devuan Jessie (which is basically the same as Debian 8 Jessie), 64-bit, and I have stack installed using the script provided by the stack website, and GHC installed using `stack setup`. I'm trying to build the very same program, and I get this: Configuring HsOpenSSL-0.11.1.1... Cabal-simple_mPHDZzAJ_2.0.1.1_ghc-7.10.3: Missing dependencies on foreign libraries: * Missing C libraries: crypto, ssl This problem can usually be solved by installing the system packages that provide these libraries (you may need the "-dev" versions). If the libraries are already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where they are. I thought maybe my OpenSSL version is too old. That's a bit weird because it seems to be more recent than the Trisquel one (well, basically same version, just some micro version being a bit higher), but still, I decided to try a few things: - I installed OpenSSL 1.1 using Guix and used the flags mentioned above to point to Guix's include and dir paths - I downloaded OpenSSL 1.1 release tarball, built from source, installed, pointed stack to that location - In those extra dirs I listed all the system ones like /lib and /usr/lib just in case - I updated stack to the latest release, and did stack setup --upgrade-cabal and installed alex and happy because stack complained no package was providing them - I deleted .stack-work and ~/.stack and did a totally clean build But nothing works, I'm still getting this error. On the older laptop everything works. How do I go about solving this? I don't know what else to try or how to make `stack build` look in the paths I provide and see the OpenSSL library there and use it. Thanks in advance for any clues!!! -- fr33

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No instance - but it could just put one in the context
by Tom Ellis 24 Feb '18

24 Feb '18

I'm puzzled by GHC's behaviour in the following program. 'baz = bar . foo' does not work because there is "no instance for ...". But if I manually assume those instances in the context all is fine. Why can GHC not infer that context? Is there any extension or clever trick I can use to get this to infer like I want? Thanks, Tom {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE FlexibleContexts #-} class Foo a b class Bar a b type family Quux a foo :: ( Foo a b , b ~ Quux a ) => a -> Quux a foo = undefined bar :: Bar a b => a -> b bar = undefined -- Doesn't work -- No instance for (Bar (Quux a0) c0) arising from a use of ‘bar’ -- No instance for (Foo a0 (Quux a0)) arising from a use of ‘foo’ --baz = bar . foo baz' :: ( Foo a (Quux a) , Bar (Quux a) b ) => a -> b baz' = bar . foo

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runGet exits prematurely
by Quentin Liu 23 Feb '18

23 Feb '18

Hi, I am using Data.Binary to decode binary files and found that the `runGet` function would throw an exception “not enough bytes” even though it has not consumed all the input. Specifically, in the loop I am repeatedly trying to parse the binary file until it has consumed all the input parsePPackets xs = do empty <- isEmpty if empty then return xs else do p <- parseB6034 parsePPackets (p:xs) When I try to run this function with `runGet`, the exception “Data.Binary.Get.runGet at position 3293603: not enough bytes” would be thrown, while the total length of input is 5864230, a number significantly larger. The function `parseB6034` consumes no more than 250 bytes in each round. In addition, the `parsePPackets` works well when fed with a small amount of data. Is it the problem of my code or an error with the package binary? The ByteString fed into `runGet` is lazy ByteString, as required by `runGet` function. Best Regards, Qingbo Liu

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Occurs check: cannot construct the infinite type - but it doesn't need to
by Tom Ellis 23 Feb '18

23 Feb '18

I have run into a similar problem to my last question which is not resolved with NoMonomorphismRestriction. 'foo2' has a partial type signature and I get an occurs check. 'foo3' is exactly the same except it has no signature, and it works! Why can't 'foo2' be inferred like 'foo3'? {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE PartialTypeSignatures #-} {-# LANGUAGE NoMonomorphismRestriction #-} type family Quux a type family Corge a foo :: ( b ~ Quux a , a ~ Corge b ) => a -> b foo = undefined -- Occurs check: cannot construct the infinite type: -- t0 ~ Corge (Quux t0) -- arising from a use of ‘foo’ -- The type variable ‘t0’ is ambiguous -- foo2 :: _ foo2 = foo foo3 = foo

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Re: [Haskell-cafe] [Haskell] ANN: Hackage Account Registration Changes
by Niklas Hambüchen 23 Feb '18

23 Feb '18

On 23/02/2018 00.27, Matthias Kilian wrote: > Does it > maen that one can't trust *any* package on hackage.haskell.org at > least a little bit (based on trust between acknowledging persons > and reputation) without reviewing the package's source code? Yes, in fact you cannot trust any random code you download from the Internet, Hackage is no exception. Anybody could register and upload a package that runs some `runIO` TemplateHaskell which deletes your entire home directory upon compilation, no matter if they are verified as a human or not. Other programming languages' ecosystems don't solve this problems either; if we want it solved, we should layer a trusted curated package repository on top where all code is reviewed by a set of trusted experts.

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ThEdu'18: Call for Extended Abstracts & Demonstrations
by Achim D. Brucker 23 Feb '18

23 Feb '18

(Apologies for duplicates) Call for Extended Abstracts & Demonstrations ************************************************************************** ThEdu'18 Theorem proving components for Educational software 18 July 2018 http://www.uc.pt/en/congressos/thedu/thedu18 ************************************************************************** at FLoC 2018 Federated Logic Conference 2018 6-19 July 2018 Oxford, UK http://www.floc2018.org/ ************************************************************************** THedu'18 Scope: Computer Theorem Proving is becoming a paradigm as well as a technological base for a new generation of educational software in science, technology, engineering and mathematics. The workshop brings together experts in automated deduction with experts in education in order to further clarify the shape of the new software generation and to discuss existing systems. Invited Talk Julien Narboux, University of Strasbourg, France Important Dates * Extended Abstracts: 15th April 2018 * Author Notification: 15th May 2018 * Workshop Day: 18 July 2018 Topics of interest include: * methods of automated deduction applied to checking students' input; * methods of automated deduction applied to prove post-conditions for particular problem solutions; * combinations of deduction and computation enabling systems to propose next steps; * automated provers specific for dynamic geometry systems; * proof and proving in mathematics education. Submission We welcome submission of extended abstracts and demonstration proposals presenting original unpublished work which is not been submitted for publication elsewhere. All accepted extended abstracts and demonstrations will be presented at the workshop. The extended abstracts will be made available online. Extended abstracts and demonstration proposals should be submitted via easychair, https://easychair.org/conferences/?conf=thedu18 formatted according to http://www.easychair.org/publications/easychair.zip Extended abstracts and demonstration proposals should be approximately 5 pages in length and are to be submitted in PDF format. At least one author of each accepted extended abstract/demonstration proposal is expected to attend THedu'18 and presents his/her extended abstract/demonstration. Program Committee Francisco Botana, University of Vigo at Pontevedra, Spain Roman Hašek, University of South Bohemia, Czech Republic Filip Maric, University of Belgrade, Serbia Walther Neuper, Graz University of Technology, Austria (co-chair) Pavel Pech, University of South Bohemia, Czech Republic Pedro Quaresma, University of Coimbra, Portugal (co-chair) Vanda Santos, CISUC, Portugal Wolfgang Schreiner, Johannes Kepler University, Austria Burkhart Wolff, University Paris-Sud, France Proceedings The extended abstracts and system descriptions will be available in ThEdu'18 Web-page. After presentation at the conference, selected authors will be invited to submit a substantially revised version, extended to 14--20 pages, for publication by the Electronic Proceedings in Theoretical Computer Science (EPTCS). -- Dr. Achim D. Brucker | Software Assurance & Security | University of Sheffield https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Re: [Haskell-cafe] [Haskell] ANN: Hackage Account Registration Changes
by Gershom B 23 Feb '18

23 Feb '18

(Replying just on -cafe. The other cc's shouldn't be included in the follow-on discussion to this announcement). A PR to augment links with nofollow tags would be welcome. Note that for completeness this would have to be done in the markdown engine, the package-description rendering engine, _and_ the haddock generation, which are three distinct codepaths. That said, I think that does not suffice, as I do not think the intent of the spam is _just_ to perform search engine optimization. And further, I have seen other cases as well where people are undeterred by SEO-prevention measures. For example, we require manual approval of wiki.haskell.org accounts despite the addition of nofollow tags, as those did not deter spammers in that case. The current policy is not a "direction" we are taking -- it is an interim measure until a better fix can be put in place. There is some discussion of what a "better fix" might look like on an issue on hackage-server: https://github.com/haskell/hackage-server/issues/685 -g On Thu, Feb 22, 2018 at 7:26 PM, Geoffrey Huntley <ghuntley(a)ghuntley.com> wrote: > I feel that this is the wrong direction to take and will add more burden on > people that we shouldn't be adding additional burden to. It's also the wrong > "optics". > > I just had a quick squizz at Hackage with a simple PR you'll be able to > remove the incentives for this behaviour. > > Add "nofollow" to any links supplied by the user or that are rendered as > part of parsing user input. > > https://support.google.com/webmasters/answer/96569?hl=en > > The .NET ecosystem recently went through these same notions for the same > reasons - here's the PR > > https://github.com/NuGet/NuGetGallery/pull/4841/files > > On Fri., 23 Feb. 2018, 10:38 am Matthias Kilian, <kili(a)outback.escape.de> > wrote: >> >> Hi, >> >> On Thu, Feb 22, 2018 at 05:54:33PM -0500, Gershom B wrote: >> > In the meantime, as a short term measure, we have changed new account >> > registration policies on hackage. >> > >> > Users can still register as before, but new users do _not_ have upload >> > rights until they explicitly request them and are granted them by a >> > human being. >> > >> > (This is actually how we had configured hackage to work on initial >> > deployment -- we loosened things up for some years as the extra step >> > seemed unnecessary). >> >> Does this mean that before the todays change, anyone (or anything) >> could register and upload packages without any review and without >> any acknowledgement for trustfulness by another person? Does it >> maen that one can't trust *any* package on hackage.haskell.org at >> least a little bit (based on trust between acknowledging persons >> and reputation) without reviewing the package's source code? >> >> Ciao, >> Kili >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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ANN: Hackage Account Registration Changes
by Gershom B 23 Feb '18

23 Feb '18

As some people have seen, a spammer has started to create accounts on hackage to upload fake packages, in order to use their package-descriptions for linkspam. We'll be working to clean-up the package-index from this spam, and the accounts have been disabled. Further, we'll need to decide on some long-term changes going forward to make this sort of abuse more difficult. In the meantime, as a short term measure, we have changed new account registration policies on hackage. Users can still register as before, but new users do _not_ have upload rights until they explicitly request them and are granted them by a human being. (This is actually how we had configured hackage to work on initial deployment -- we loosened things up for some years as the extra step seemed unnecessary). Apologies for the inconvenience, but this seemed the most direct way to stop the current influx of spam. Users with existing hackage accounts should encounter no differences in behavior. Best, Gershom

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