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Announcing libravatar < at > hackage

haskell-cafe - Sun, 07/12/2015 - 8:09pm
Hello! Libravatar - - is a free-as-in-freedom and decentralized avatar (profile image delivery service, a replacement of the centralized and proprietary grava7ar. There has been a Haskell library for grava7ar for some time, but not for Libravatar. I just finished writing one, and did a bit of testing which had good results. More testing and feedback etc. very very welcome! I also enourage you all to *integrate libravatar into your desktop/web applications and websites*! Support openness, decentralization and freedom by using Libravatar. --- fr33domlover <> GPG key ID: 63E5E57D (size: 4096) GPG key fingerprint: 6FEE C222 7323 EF85 A49D 5487 5252 C5C8 63E5 E57D _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe< at >
Categories: Offsite Discussion

On Windows after I install the new cabal-install then when I do a cabal update it says there is a new ...

haskell-cafe - Sun, 07/12/2015 - 6:28pm
On Windows after I install the new cabal-install then when I do a cabal update it says there is a new cabal-install available. Yet cabal-install installed without any errors. Why do I get this message? -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe< at >
Categories: Offsite Discussion

AI4FM 2015: Final call for short contributions

General haskell list - Sun, 07/12/2015 - 2:48pm
AI4FM 2015 The 6th International Workshop on the use of AI in Formal Methods *1st September 2015 in Edinburgh, Scotland.* In association with AVoCS 2015 ( Important dates ---------- *Submission deadline: 1st August 2015* Notification of acceptance: 10th August 2015 Final version due: 21st August 2015 Workshop: 1st September 2015 Overview ---------- The 6th International Workshop on the use of AI in Formal Methods (AI4FM 2015) will be held on the 1st of September, 2015 in Edinburgh, Scotland. The AI4FM workshops bring together researchers from formal methods, automated reasoning and AI; aiming to address the issue of how AI can be used to support the formal software development process, including requirement analysis, modelling and proof. The workshops include a mix of industrial and academic participants and we anticipate attracting a similarly diverse audience in AI4FM 2015. We invite 3-page short contributions (extended abs
Categories: Incoming News

mp4v2 bindings for Haskell?

Haskell on Reddit - Sun, 07/12/2015 - 2:42pm

Another relative newcomer to haskell, I'm rewriting a media management system for my home video library that I originally wrote in Python as a way to work through concepts in LYAH and RWH. It's taken me a few weeks to get the basic concepts solid, and work through some differences between the code in RWH and what works in the current platform.

At this point, I need some functions that will read tags from .mp4/.m4v videos. I tried TagLib that I found on hackage,but that doesn't seem to work with videos (and only mentions audio in the docs). Does anyone know of any haskell bindings for the mp4v2 library, or of any library that will read mp4 video tags in haskell?

My other choice is to start to rewrite something like Python's mutagen in haskell, but I'm not quite sure I'm ready for that.

submitted by rogue203
[link] [5 comments]
Categories: Incoming News

Daniil Frumin: Darcs 2.10.1 (Mac OSX build)

Planet Haskell - Sun, 07/12/2015 - 12:13pm

Darcs 2.10.1 has been released!

Citing the official release notes

> The darcs team is pleased to announce the release of darcs 2.10.1 ! > .. > > # What's new in 2.10.1 (since 2.10.0) # > > - generalized doFastZip for darcsden support > - support terminfo 0.4, network 2.6, zlib 0.6, quickcheck 2.8 and > attoparsec 0.13 > - errorDoc now prints a stack trace (if profiling was enabled) (Ben Franksen) > - beautified error messages for command line and default files (Ben Franksen) > - fixed the following bugs: > - issue2449: test harness/shelly: need to handle > mis-encoded/binary data (Ganesh Sittampalam) > - issue2423: diff only respecting --diff-command when a diff.exe > is present (Alain91) > - issue2447: get contents of deleted file (Ben Franksen) > - issue2307: add information about 'darcs help manpage' and > 'darcs help markdown' (Dan Frumin) > - issue2461: darcs log --repo=remoterepo creates and populates > _darcs (Ben Franksen) > - issue2459: cloning remote repo fails to use packs if cache is > on a different partition (Ben Franksen) > > # Feedback # > > If you have an issue with darcs 2.10.0, you can report it on > . You can also report bugs by email to > bugs at, or come to #darcs on

I’ve updated Mac OS to version 2.10.1. You can install it with

brew install
Tagged: darcs, haskell, homebrew
Categories: Offsite Blogs

Problems with Numeric.Matrix module

Haskell on Reddit - Sun, 07/12/2015 - 12:12pm

I just installed Haskell Platform 2014.2.0.0 (x64) for Windows. I tried to load Numeric.Matrix into GHCi to play around. It wouldn't compile, giving this error on 161:5:

'typeOf' is not a (visible) method of class 'Typeable'

So I commented out the instance that was causing the problem:

instance Typeable a => Typeable (Matrix a) where typeOf x = mkTyConApp (mkTyCon3 "bed-and-breakfast" "Numeric.Matrix" "Matrix") [typeOf (unT x)] where unT :: Matrix a -> a unT = undefined

This allowed it to load into GHCi with a warning:

The import of 'Data.Typeable' is redundant except perhaps to import instances from 'Data.Typeable'

I instantiated a matrix:

> let m = fromList [[1.0,5.0,9.0],[3.0,5.0,7.0],[6.0,4.0,8.0]]

which worked, then tried to compute its determinant

> det m

which crashed GHC. Has anyone gotten this module to run smoothly?

submitted by lithiumdeuteride
[link] [2 comments]
Categories: Incoming News

Using newtypes or any data with unboxed Vectors

libraries list - Sun, 07/12/2015 - 7:54am
I think I've managed to come up with an easy, useful, and sound way for mere mortals to use unboxed vectors with arbitrary datatypes, without using template Haskell. I had a need for this capability, googled about it, and I didn't find a satisfying way to do it. This technique seemed useful and simple enough to go into the vector library, but there's so much stuff going on in there I'm not ready to submit a patch. A user just needs to create an UnboxEquivalent instance for their type, and then they can work with what looks and acts like a vector of their type, but is in fact backed by a newtype-wrapped unboxed vector of the equivalent type. newtype SmallPos = Pos Int deriving (Eq, Ord, Show) smallPos :: Int -> SmallPos smallPos x | x > 0 && x < 100 = Pos x | otherwise = error "bad SmallPos" instance UnboxEquivalent SmallPos where type UnboxEquiv SmallPos = Word8 toUnbox (Pos x) = fromIntegral x fromUnbox x = (Pos (fromIntegral x)) test1 :: EVector SmallPos test1 = Data.Vecto
Categories: Offsite Discussion

Free, cofree, and IO

Haskell on Reddit - Sun, 07/12/2015 - 7:23am

I've been writing a series of posts on using the free monad for DSLs and cofree comonads for the corresponding interpreters.

I've written a bit about bringing IO into that mix here.

Hopefully some folks find it interesting and/or useful. Let me know if you have any comments / feedback / criticism.

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

When can we expect the next version of the Haskell Platform?

Haskell on Reddit - Sun, 07/12/2015 - 2:13am

Right now we're still on 2014.2.0.0. When is 2015.4.0.0 shipping? Will it have GHC 7.10.2?

submitted by bitmadness
[link] [3 comments]
Categories: Incoming News

Mockup of a redesigned /r/haskell (based on the new

Haskell on Reddit - Sun, 07/12/2015 - 1:09am

Hi guys! I'm an ultra-noob to Haskell (still working my way through LYAH) but I'm falling in love with the language and I'm really enjoying learning!

Since I can't really do anything in Haskell to help out the community, I thought I could contribute with a potential redesign of the subreddit, based on the updated website design over at

I've spent a few hours making a mockup of what the subreddit could look, using a modified version of the /r/Naut subreddit theme. I think it would be really nice to have a more consistent design across the website and this subreddit, and Naut brings a lot of the modern, clean design we see on the updated website here.

I'd appreciate hearing your opinions, and I will try to make whatever modifications needed to fit the needs or /r/haskell.

TL;DR: Check it out here:

UPDATE 7/12/15: This is how it would look on the actual /r/haskell and not my test subreddit (with it's sparse posts):

You can try it out yourself if you have the Stylish browser extension by making a new style and pasting this gist in:

submitted by evanrelf
[link] [31 comments]
Categories: Incoming News

SQL database schema diff tool

haskell-cafe - Sat, 07/11/2015 - 6:54pm
Hi, list! I wish I have a tool which would compare two database sachemas, where each schema is represented as a list of 'CREATE smth' instructions. The result of such a comparison would be a list of 'ALTER smth' instructions. This instruction set would change the database from first state to second, if the transition is possible without data losses. The 'hard' mode - to prepare the transition for any inputs, with minimal data losses. The database of interest is PostgreSQL. Does such a tool exist? If not, which package do I better use to build the AST of initial schemas? The example schema is in attach. Thanks in advance, Sergey _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe< at >
Categories: Offsite Discussion

Calculus in Haskell?

Haskell on Reddit - Sat, 07/11/2015 - 5:56pm

When I learned Group Theory I found a really good exercise was expressing the Rubik's Group in Haskell. It was particularly interesting to think about efficient ways of representing permutation groups and coming up with a notation in Haskell that matched the mathematical notation.

I've recently started learning some calculus and I was thinking about trying to do something similar. But I'm not really sure where to start. And I'm having trouble finding calculus in packages (everything I've found is lambda calculus).

My line of thinking was something like this... calculating the derivative takes a function (x -> t) to the derivative dx/dt. This seems like an Endofunctor DxDt t x (also a Bifunctor and Contravariant Functor?). Further, you can take additional derivatives of a derivative, which suggests to me a Monadic bind/join possibility on DxDt t (DxDt t x). I don't know enough Category theory to take that thought any further though. E.g. is the Comonad indefinite integration?

Additionally the largely mechanical integration / differentiation rules seem like combinators. Particularly when it comes to things like the chain rule or for more complex things like linear DEs. I imagine you could apply a parser combinator over a function to find its derivative provided it was formulated properly.

Rather than a paper on the subject (which would almost certainly be too dense for me) are there any blog posts / Hackage packages that could shed some light on where to continue this mini-project? Also any comments on whether any of the above is remotely correct?

submitted by TheCriticalSkeptic
[link] [21 comments]
Categories: Incoming News

ANN: transformers-lift

Haskell on Reddit - Sat, 07/11/2015 - 4:27pm

The transformers package defines lifting operations for each monad transformer. Those lifting operations have common type signatures and laws they obey -- just what a type class method needs. However, for some reason they're not type class methods but completely separate functions, and their signatures and laws are defined in a separate module (Control.Monad.Signatures).

The transformers-lift defines the type classes for lifting monad transformers operations and also adds missing instances (so now you can lift catch through ExceptT, pass and listen through WriterT and RWST, and more).

The package is extremely lightweight, so if your library defines custom monad transformers, consider adding instances for transformers-lift.

submitted by int_index
[link] [4 comments]
Categories: Incoming News

Anything like find-by-example from Pharo Smalltalk in Haskell?

Haskell on Reddit - Sat, 07/11/2015 - 3:10pm

Just watched 7 minutes of Pharo Smalltalk for Rubyists and thought that Haskell obviously should have something like it (If it already does it should be advertised a bit better). Also, Hoogle is great and would greatly benefit from something like this integrated into it (alongside Djinn).

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

Looking to start or join hobby projects with other people in order to learn Haskell

Haskell on Reddit - Sat, 07/11/2015 - 2:59pm

Just wondering, is there anyone interested in working together (or need some help?) in any hobby project based in Haskell? I don't have anything specific in mind, just something we could agree on. I'm a Haskell beginner who already read LYAH and most of RWH, as well as many other tutorials and blog posts around the web. I believe the best way to learn a language is to actually write some real world code with it (being a mobile developer myself, working on the backend/web side of an app in Haskell is something appealing, but I'm open to suggestions).

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

Final CF STUDENT POSTERS for Innovations'15 (No registration fees), Dubai, November 01-03, 2015

General haskell list - Sat, 07/11/2015 - 9:25am
IIT’15: The 11th International Conference on Innovations in Information Technology 2015 URL: The IIT’15 Student Poster and Demos Committee invites all undergraduate and graduate students to submit an extended (2 pages max.) abstract and to display it as a poster during the IIT’15. The poster topic should fall within the conference’s theme and tracks. SUBMISSION Extended abstracts should be sent to Dr. Nabeel Al-Qirim at nalqirim< at > All students are encouraged to review their abstracts with their faculty advisers prior to submission. All accepted abstracts will be published by the IIT’15 proceedings. NEW IMPORTANT DATES -Student Poster (Extended Paper) Submission July 15, 2015 -Notification of Student Poster acceptance from September 9, 2015 -Camera ready Extended Paper and Poster material September 29, 2015 -Conference November 01-03, 2015 BEST STUDENT POSTER AWARDS There will be a competition for best stud
Categories: Incoming News