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Brent Yorgey: BlogLiterately 0.8.1, now with HTTPS!

Planet Haskell - Mon, 06/01/2015 - 8:52pm

I’ve just released version 0.8.1 of BlogLiterately, a tool for formatting and posting stuff (especially Haskelly stuff) to blogs. This is in conjunction with the release of haxr-3000.11. After much blood, sweat, and tears, I was able to rip the HTTP package out of the guts of haxr, replace it with http-streams, and carefully sew everything back together around the edges. The result is that haxr now finally supports making XML-RPC calls via HTTPS, which in turn means that BlogLiterately once again works with WordPress, which no longer supports XML-RPC over HTTP. Happy blogging!

Categories: Offsite Blogs

Magnus Therning: Facebook and PGP

Planet Haskell - Mon, 06/01/2015 - 6:00pm

I wonder if this will have any impact at all on PGP usage… I doubt it, but it’s still nice to see it done. The Register also writes about it.

Categories: Offsite Blogs

Vincent Hanquez: Announcing: cryptonite

Planet Haskell - Mon, 06/01/2015 - 6:00pm

For the last 5 years, I’ve worked intermittently on cryptographic related packages for Haskell. Lately, I’ve consolidated it all in one single package. Announcing cryptonite

This new package merges the following packages:

Also this package adds support for the following features:

Why this new packaging model ?

This is mostly rooted in three reasons:

  • Discoverability
  • Cryptographic taxonomy
  • Maintenance

Discovering new packages in our current world of hackage is not easy. Unless you communicate heavily on new packages, there’s a good chance that most people would not know about a new package, leading to re-implementation, duplicated features, and inconsistencies.

Cryptography taxonomy is hard, and getting harder; cryptographic primitives are re-used creatively for making hash from cipher primitive, or random generator from cipher, or authentification code from galois field operations. This does create problems into where the code lives, how the code is tested, etc.

Then, finally, if I have to choose a unique reason for doing this, it will be maintenance. Maintenance of many cabal packages is costly in time: lower bounds, upper bounds, re-installation, compatibility modules, testing framework, benchmarking framework.

My limited free time has been siphoned into doing unproductive cross packages tasks, for example:

  • Upgrading bounds
  • Sorting out ghc database of installed-packages when reinstalling packages for testing features
  • Duplicating compatibility modules for supporting many compilers and library versions
  • Maintaining meta data for many packages (e.g. LICENSE, CHANGELOG, README, .travis, .cabal)
  • Tagging and releasing new versions

Doing everything in one package, simplifies the building issues, gives a better ability to test features easily, makes a more consistent cryptographic solution, and minimizes meta data changes.

What happens to other crypto packages ?

Cryptonite should be better in almost every aspect: better features, better testing. So there are no real reasons to maintain any of the old packages anymore, so in the long run, I expect most of those packages to become deprecated. I encourage everyone to move to the new package.

I’ll try to answer any migration questions as they arise, but most of the migration should be straightforward in general.

I’m committed to maintain cryptohash for now, as it is very widely used. I’ll try to maintain the rest of the packages for now, but don’t expect this to last for long.

Otherwise, If some people are interested in keeping certain other pieces independent and maintained, come talk to me directly with motivated arguments.


I hope this does bring contributions, and this becomes a more community-maintained package, and specially that cryptonite becomes the canonical place for anything cryptography related in Haskell.

Main things to look out, for successful contributions:

  • respect the coding style
  • do not introduce dependencies

Also you don’t need to know every little thing in cryptography to help maintain and add feature in cryptonite.

PS: I’m also looking forward to more cryptography related discussions about timing attacks, what source of random is truly random, etc. :-þ

Categories: Offsite Blogs

Arithmetic overflow in rem and mod

glasgow-user - Mon, 06/01/2015 - 5:40pm
According to the documentation, rem and mod must satisfy the following laws: -- > (x `quot` y)*y + (x `rem` y) == x rem -- > (x `div` y)*y + (x `mod` y) == x mod Note, however, that there is a case when quot and div result in an arithmetic overflow: Prelude> (minBound :: Int) `quot` (-1) *** Exception: arithmetic overflow Prelude> (minBound :: Int) `div` (-1) *** Exception: arithmetic overflow while rem and mod don't: Prelude> (minBound :: Int) `rem` (-1) 0 Prelude> (minBound :: Int) `mod` (-1) 0 Is this a mistake? For the record, I'm aware of the safeint package, which raises the error for rem and mod, and this ticket:
Categories: Offsite Discussion

Free and Cofree

Haskell on Reddit - Mon, 06/01/2015 - 5:27pm

I recently gave a talk - "Cofun with cofree comonads" - at YOW! Lambda Jam in Brisbane, and promised I'd start writing some blog posts expanding on the content of the talk and the lengthy queue of associated ideas I've been playing with.

The first post is here.

I'm planning to post the next few posts in the series once a week, to buy more time to work on the posts after that. Looking at comonad / comonad transformer / cofree comonad performance and looking at how cofree comonads interact with QuickCheck are both on the queue, along with a lot of fun (to me) little side avenues.

Hopefully some of the ideas in the series will be useful to people. Feedback, comments and criticism are all welcome.

submitted by dalaing
[link] [15 comments]
Categories: Incoming News

cabal-install: bug and quest for a workaround

libraries list - Mon, 06/01/2015 - 4:58pm
Hi, I have just installed GHC 7.10.1 and cabal-install The problem is that cabal-install often hangs when trying to download a package. With --verbose=3, I see that it gets a “301 Moved Permanently” from the server, tries to redirect, shows “Recovering connection to”, and then hangs. Is there anything I can do to work around this issue? At the moment, I cannot work with my new GHC installation, since it is virtually impossible to install packages with cabal-install. All the best, Wolfgang _______________________________________________ Libraries mailing list Libraries< at >
Categories: Offsite Discussion

ANN: toysolver 0.3.0 released

haskell-cafe - Mon, 06/01/2015 - 12:05pm
Dear all, I'm announcing the release of the toysolver package. It provides solver implementations of various problems including SAT, Max-SAT, PBS (Pseudo Boolean Satisfaction), PBO (Pseudo Boolean Optimization), MILP (Mixed Integer Linear Programming) and non-linear real arithmetic. In particular it contains moderately-fast pure-Haskell SAT solver 'toysat'. It can also be used as a backend for ersatz and satchmo. Regards,
Categories: Offsite Discussion

Month in haskell mode May 2015

Haskell on Reddit - Mon, 06/01/2015 - 11:03am
Categories: Incoming News

HughesPJ pretty print question

Haskell on Reddit - Mon, 06/01/2015 - 10:59am

Does anybody used pPrint with HughesPJ library? I got a little question

submitted by patolin_01
[link] [5 comments]
Categories: Incoming News

Stackage LTS Haskell prebuilt Docker images and Wercker boxes

Haskell on Reddit - Mon, 06/01/2015 - 10:00am

I've created prebuilt Wercker box and Docker images and for the two branches of Stackage's LTS Haskell: 1.15 and 2.11 as of today.

These images/boxes are preconfigured to use the respective Stackage branch:

There are also images available with preinstalled packages. (However, since Stackage has grown considerably, it is not possible to install all the packages in LTS Haskell in one go, and so these only contain the 250 most popular ones.)

I hope you will find them useful. If you have any comments, suggestion or advice, please let me know. And thanks to all the people who work (not only) on Stackage and made this possible.


as I implied, I tried to build all of the stackage and timeouted

Categories: Incoming News

Well-Typed.Com: Cabal & Hackage hacking at ZuriHac

Planet Haskell - Mon, 06/01/2015 - 9:35am

At ZuriHac this weekend we had eight people hacking on Cabal or Hackage, many of whom are new contributors. There were a number of projects started as well as a number of smaller fixes completed.

In addition, there are three Google Summer of Code students working on Cabal and Hackage projects this summer:

They’re all just getting started, so more news about them later. All in all there seems to be a decent amount of progress at the moment across a range of issues. In particular we’re getting closer to solving some of the thornier “Cabal Hell” problems.

Heroic bug squashing

Oleg Grenrus was a bit of a hero in that as a new Cabal contributor, over two days of the hackathon, he managed to send in pull requests to fix five open tickets.

Another couple chaps (whose names to my shame have slipped my mind) dived in to fix old tickets on sanity checking absolute/relative paths for library directories in .cabal files and config files, and on passing GHC env vars to sub-commands like in cabal run/exec/test.

These in addition to the flurry of pull requests in recent weeks, and others from the hackathon, has given the regular Cabal hackers quite a pile of patches to get through. We hope to review and merge them in the next week or so.

Integrating package security for Cabal/Hackage

The work on securing the package download process that we announced a while ago is nearing the integration phase. While it’s been useful to have a couple people concentrate on implementing the core hackage-security library, at this stage it makes sense to open the process up and get more people involved.

Matthias Fischmann had proposed it as a ZuriHac project and organised a group of people who were interested. We discussed some of the issues involved with using the new hackage-security code in the cabal-install tool, and got started on some of the tasks.

Bootstrapping repository security

With public key crypto systems there’s always a need to somehow bootstrap the trust chains. For example with the public web certificate system (used by TLS / HTTPS) the root of the trust chains is the certificate authorities. We must know and trust their public keys to be able to verify the chain of trust for any particular website. But how should we establish trust in the certificate authorities’ keys in the first place? With web browsers this bootstrapping problem is resolved by the browser (or OS) shipping pre-installed with all the CA public keys.

For hackage servers we face a similar bootstrapping problem. Hackage security does not use public certificate authorities but there is a similar root of trust in the form of a set of root keys. For the central community we can of course do the same thing as the web browsers and ship the server’s public root keys with cabal-install. But we need to support people making their own repositories and obviously we can’t ship all the public keys. So we need a convenient way for people to configure cabal-install to establish trust in a particular repository. The obvious thing is to specify the trusted public keys in the cabal configuration, where you specify the repository to use.

Currently in a cabal configuration file that part looks like:


This syntax is too limited to support adding extra attributes like keys. So what people were working on at ZuriHac was supporting something like this:

remote-repo url: keys: ed25519:9fc1007af2baff7088d082295e755102c1593cdd24b5282adbfa0613f30423f6 ed25519:7cd11f018d5211f49b2fb965f18577d7f45c0c9be2a79f5467e18d0105ac1feb ed25519:26443e74981d5b528ef481909a208178371173ff7ccee8009d4ebe82ddb09e1e

So someone hosting their own hackage repo can provide instructions with a sample cabal.config or a block of text like the above to copy and paste into their config file, for people to use to get started.

This more flexible syntax will also allow miscellaneous other repository settings such as specific mirrors to use, or the ability to turn off security entirely.


Another couple people got started on writing a mirror client using the hackage-security library. While mirroring does not need a dedicated tool it is a rather convenient and efficient approach. It means we can use the ordinary HTTP interface rather than providing rsync or another interface and we can still do very bandwidth-efficient synchronisation. The advantage over a generic HTTP mirroring tool is that we have an index of the available packages and we know that existing packages are immutable, so we can simply diff the source and target indexes and copy over the extra packages.

In fact there are already two hackage mirror clients that do this. One of them pulls from one repo and pushes to a “smart” hackage-server. The other pulls from a repo and pushes to a repo hosted via S3. What is missing is the ability to mirror to a simple local set of files. Mirrors don’t have to be full hackage-server instances or S3, they can be ordinary HTTP servers like Apache or nginx that point at a set of files in the right layout. The hackage-security library is a convenient tool to use to write this kind of mirror since it handles all the details of the repository layout, and it supports doing incremental updates of the repository index. In this use case the security checks are merely sanity checks, as in the end, clients downloading from this mirror do their own checks.

So the work started by taking the existing hackage-server mirror and hackage-security demo client with the goal of replacing (or extending) the guts of the mirror client to use the hackage-security lib to download and to be able to manage a target repo as a set of local files.

Once the security work is integrated it will become much more useful to have public mirrors because clients then don’t need to trust the mirrors (we’re safe from MITM attacks). And hackage will distribute a list of public mirrors that the clients will use automatically. So having a decent mirroring client will become rather important. It’s also useful for the synchronisation to be very efficient so that the public mirrors can be nearly live copies.

Solving the cabal sandbox / global packages problem

A problem that people have been complaining about recently is that the Haskell Platform ships with lots of packages in the global package database, making it hard to compile packages that require non-standard versions of the platform packages.

This isn’t really a problem with the Haskell Platform at all, it’s really a problem with how cabal-install constructs its sandboxes, and fortunately it’s one that seems relatively easy to fix. Good progress was made on this ticket over the hackathon and hopefully it will be completed within the next couple weeks.

The problem is that cabal sandbox init makes an environment where with a package database stack consisting of the global one, plus a new empty local one. This means all the global packages are implicitly inside the sandbox already. That’s not so useful when you want to start with a minimal sandbox.

Originally this was a GHC limitation, that we always had to use the global package DB, however that has been fixed now for a couple GHC releases. So the solution we went for is to use only a local empty package DB, and to copy the registration information for a certain set of core packages into the local package DB. Ultimately we would like GHC to come supplied with the list of core packages, but for now we can just hard code the list.

Improving the tagging feature on Hackage

One new contributor started work on reimplementing the Hackage website’s tagging feature to make it more flexible and useful. The key idea is to make package categories into tags and make it easier to curate tags by solving the problem that lots of tags are essentially aliases for each other. This happens because each package author picks their tags themselves. So we will have sets of tag aliases, each with a canonical representative. Then any package using any alias will be assigned the canonical tag. The data model and user interface will make it possible for trustees to decide which existing tags ought to be aliased together and then do it. Ultimately, the tags and aliases should be useful in the existing hackage search.

Supporting curated package collections in Cabal and Hackage

Curated package collections are one of the two major parts to solving Cabal Hell.

People started work on supporting these natively in Cabal and Hackage. The idea is that proper integration will make them easier to use, more flexible and easier for people to make and distribute curated collections. Examples of curated collections include stackage (LTS and nightly snapshots) and the sets of versions distributed by Linux distros. Integration will allow simpler and shorter configurations, easier switching between collections and the ability to easily define collections either to distribute on Hackage or to use locally. By teaching cabal about collections it can give better error messages (e.g. when something cannot be installed because it’s not consistent with the collection(s) in use). Making collections easier to distribute via Hackage, and easier to combine, might open up new possibilities. For example we might see collections specifically to help people work with the popular web stacks (e.g. if those cannot always fit into a large general purpose collection). Or we might see collections of things you might like to avoid such as deprecated or known-broken packages. Combining collections would then allow you to configure cabal to use a large collection intersected with the negation of the collection of deprecated packages.

Categories: Offsite Blogs

Beginner haskell project: parsing subtitles

Haskell on Reddit - Mon, 06/01/2015 - 7:18am

After hearing about how suited haskell is to write parsers, I decided to try this out and write a small subtitle (.srt file) parser. The goal is to add a given delay to a file. I didn't use one of the available parsers as I wanted to write my own.

How would you improve the code?

I specifically had trouble with:

  • Conversion time -> milliseconds : I could not wrap my head around this and finally wrote my own
  • The code in the Left/Right result of the parsing (basically everything after the -> arrow) : How does this work?


submitted by stmu
[link] [9 comments]
Categories: Incoming News

A Dockerfile to provision a build environment for an Android game written in Haskell

General haskell list - Mon, 06/01/2015 - 4:55am
Fellow Haskell users! For the last few months I've been working on a small game targeting Android devices. It's still in development and will probably change radically from what I've already done. However, in the process of developing this game I've managed to develop a Dockerfile that will provision a build environment to build the game, which I think is worth releasing to the Haskell community right away. I'd appreciate some assistance in validating that it, in fact, works. The repo containing the Dockerfile is hosted at: The repo containing the game is: Please use the latest version of Docker when you attempt to build this, at least version 1.6. Be aware that this will take a long time to build. You will need to download an image from THe Docker Hub Registry that is about 1.1G and then pull down even more files when building all the C and Haskell libraries. Be patient and if you have any issues plea
Categories: Incoming News

A Dockerfile to provision a build environment for an Android game written in Haskell

haskell-cafe - Mon, 06/01/2015 - 4:49am
Fellow Haskell users! For the last few months I've been working on a small game targeting Android devices. It's still in development and will probably change radically from what I've already done. However, in the process of developing this game I've managed to develop a Dockerfile that will provision a build environment to build the game, which I think is worth releasing to the Haskell community right away. I'd appreciate some assistance in validating that it, in fact, works. The repo containing the Dockerfile is hosted at: The repo containing the game is: Please use the latest version of Docker when you attempt to build this, at least version 1.6. Be aware that this will take a long time to build. You will need to download an image from THe Docker Hub Registry that is about 1.1G and then pull down even more files when building all the C and Haskell libraries. Be patient and if you have any issues plea
Categories: Offsite Discussion

Joachim Breitner: ZuriHac 2015

Planet Haskell - Mon, 06/01/2015 - 3:37am

Last weekend, I attended ZuriHac 2015, which was, as always, a pleasant event. I did not actually do a lot, besides some maintenance of Debian Haskell packages, but had some nice chats. It is always very motivating to hear that people read my blog, or that they found my talk (such as the Haskell Bytes talk at Galois) helpful.

My plan was to work on gipeda and I did not do much until an hour before I had to leave, when Lennard Kolmodin came around and I showed him the software. He liked it so far, so we quickly set up an instance of gipeda for the “binary” library. It is not finished yet, as more benchmarks need to be extracted from the build log. That was motivating, and I got further ideas to implement during the train ride back. If only that had happened earlier during the weekend...

Categories: Offsite Blogs

Examining Hackage: pipes

Haskell on Reddit - Mon, 06/01/2015 - 2:44am
Categories: Incoming News