June 2013 - Haskell-Cafe

HTML framework for web-ui
by Vlatko Basic 01 Oct '13

01 Oct '13

Hi, I'd like to start using web pages as the UI for apps. I found out for yesod, snapp and happstack as the candidates. Would you recommend any of them as better for app ui (not "classical" web pages)? Or maybe another one? thanks, vlatko

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An APL library for Haskell
by Simon Peyton-Jones 16 Sep '13

16 Sep '13

Friends Many of you will know the array language APL<http://en.wikipedia.org/wiki/APL_%28programming_language%29>. It focuses on arrays and in particular has a rich, carefully-thought-out array algebra. An obvious idea is: what would a Haskell library that embodies APL's array algebra look like? In conversation with John Scholes and some of his colleagues in the APL community a group of us developed some ideas for a possible API, which you can find on the Haskell wiki here: http://www.haskell.org/haskellwiki/APL However, we have all gone our separate ways, and I think it's entirely possible that that the idea will go no further. So this message is to ask: * Is anyone interested in an APL-style array library in Haskell? * If so, would you like to lead the process of developing the API? I think there are quite a few people who would be willing to contribute, including some core gurus from the APL community: John Scholes, Arthur Whitney, and Roger Hui. Simon

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Haskell / Functional Programmers Group in Madrid (Spain)?
by Alejandro Serrano Mena 04 Sep '13

04 Sep '13

Hi, Is there any Haskell or functional programmers user group in the region of Madrid? If not, I think it could be a great idea to get to know each other, and share experiences. Furthermore, we could try to organize some meetings with presentations, hackatons and so on (my personal ambition is to be able to organize another "ekmett Workshop" as the Japanese one - http://comonad.com/reader/2013/japanese-workshop-1/) I know there is some locations along Madrid dedicated to open source promotion, like http://madridonrails.com/, and which we could use for these meetings. I'm really looking forward to hearing from you! PS: Maybe a bare "Haskell" group is not big enough (at least according to Haskellers.com) but a "functional programmers" one may well be.

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Installling Leksah on ghc7.6.3 with haskell-platform 2013?
by Carlo Hamalainen 10 Aug '13

10 Aug '13

Hi, I'm trying to install Leksah from hackage on my Debian testing laptop, which has ghc 7.6.3 and the Haskell Platform 2013. I fixed a bunch of errors about "catch" not being exported from the Prelude, but now I'm stuck on these two errors in leksah-server-0.8.0.5: [10 of 13] Compiling IDE.Utils.GHCUtils ( src/IDE/Utils/GHCUtils.hs, dist/build/IDE/Utils/GHCUtils.o ) src/IDE/Utils/GHCUtils.hs:94:40-62: Not in scope: data constructor `Opt_ReadUserPackageConf' src/IDE/Utils/GHCUtils.hs:161:44-50: Not in scope: data constructor `Opt_Cpp' Perhaps you meant one of these: `Opt_CSE' (imported from GHC), `Opt_Pp' (imported from GHC) Where have Opt_ReadUserPackageConf and Opt_Cpp gone in ghc 7.6.3? Cheers, -- Carlo

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Re: [Haskell-cafe] [Haskell] Spam on the Haskell wiki
by Henk-Jan van Tuyl 03 Aug '13

03 Aug '13

On Mon, 16 Jul 2012 00:03:49 +0200, Henk-Jan van Tuyl <hjgtuyl(a)chello.nl> wrote: > > I am willing to do administrator tasks. > >> 4. ReCAPTCHA enabled for 'edits adding new, unrecognized external >> links' - which is all of the spam. > > This is already enabled. The HaskellWiki is still flooded with spam; we should take some measure to reduce the stream severely. Most spam seems to be created (semi-)automated; the pages do not contain links, the usernames end with two digits, most of the time. Some cures I have thought up: - Verify new wiki accounts, before granting them rights, based on e-mails in the Haskell mailing lists (or subscription of a Haskell mailing list) - Let new users only change pages, not create new pages - Block creation of usernames o ending with two or more digits o with more than one x or q o starting with "buy" o longer than 20 characters o with more than 4 consonants in a row - Block creation of pages with words in a certain list (Coach, Vuitton, Chanel, handbags, purses, outlet, luggage, "Nike Air Jordan") Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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[ANNOUNCE] fficxx : haskell-C++ FFI binding generator
by Ian-Woo Kim 02 Aug '13

02 Aug '13

Dear Haskellers, Hello. I am very happy to announce the first version of fficxx (http://ianwookim.org/fficxx, also, please look at http://github.com/wavewave/fficxx ) fficxx is a haskell Foreign Function Interface (FFI) generator to C++. This tool automatically generates haskell FFI package for a given C++ class structure. It has been used for generating my haskell binding to the ROOT library [1] called HROOT [2]. Now I made it as a separate tool to benefit everyone trying to make a haskell-C++ binding. I am going to explain how to use the library/tool one by one in my blog ( http://ianwookim.org/blog ). Currently, in the fficxx cabal package, I provide a very simple sample in the sample directory. If interested, please try this and give me some comments on it in the discussion mailing list: http://ianwookim.org/fficxx/discuss.html I hope that this is useful to many haskellers. Have fun with it! Thanks, Ian-Woo Kim (wavewave) [1] : http://root.cern.ch [2] : http://ianwookim.org/HROOT

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Monad Transformer Space Leak
by Clark Gaebel 18 Jul '13

18 Jul '13

Hi everyone! For some reason, this leaks thunks: module Main where import Control.Monad import Control.Monad.MC -- from monte-carlo import Control.Monad.ST.Strict go :: Int -> MCT (ST s) () go k = replicateM_ k (return ()) main = print $ runST $ evalMCT (go 100000000) rng where rng = mt19937 0 while this does not: module Main where import Control.Monad import Control.Monad.MC go :: Int -> MC () go k = replicateM_ k (return ()) main = print $ evalMC (go 100000000) rng where rng = mt19937 0 Can anyone help me figure out what's going on here? Thanks, - Clark

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Re: [Haskell-cafe] Optimization flag changing result of code execution
by Azeem -ul-Hasan 18 Jul '13

18 Jul '13

I am using GHC 7.6.1 mwc-random 0.12.0.1 vector 0.9.1 primitive 0.4.1 Azeem On 16.03.2013 13:31, Azeem -ul-Hasan wrote: > Nope that isn't the case either. Even if I make use of defaultSeed > through create the problem still remains. The problem seems to be in the > generation of a vector of (a,a) i.e in the part > > V.generateM ((round $ p*(fromIntegral $ l*z)) `div` 2) (\i-> R.uniformR > ((0,0) , (l-1,l-1)) gen) > > in line 16. Thanks again. > I've tried to run you program and I've got approximately same results regardless of optimization level. Which versions of GHC, mwc-random, vector and primitive do you use?

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ANNOUNCE: module-management-0.9.3 - clean import lists, split and merge modules
by David Fox 16 Jul '13

16 Jul '13

I am pleased to announce the first release of module-management, a package for cleaning import lists, and splitting and merging modules. You can see a description at the top of the documentation for Language.Haskell.Modules (once it appears) here: http://hackage.haskell.org/package/module-management It is worth noting that the split and merge operations cause global changes to the module tree, all the modules that import the split or merged modules get their import lists adjusted. For this reason, before these operations can run the caller needs to specify the "moduVerse", the set of modules to scan for import changes. A number of bugs in GHC's -ddump-minimal-imports feature cropped up while I was writing this, and when the fixes for these issues make it into the compiler things will work a bit more smoothly, particularly if you are using NoImplicitPrelude or type families. http://hackage.haskell.org/trac/ghc/ticket/7963 http://hackage.haskell.org/trac/ghc/ticket/7969 http://hackage.haskell.org/trac/ghc/ticket/8000 http://hackage.haskell.org/trac/ghc/ticket/8011 There are workarounds for 7963 and 7969. Not surprisingly, template haskell can cause problems, but frequently it does not. CPP directives do not work. I hope you find this useful - all feedback is welcome! -david

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Array, Vector, Bytestring
by silvio 10 Jul '13

10 Jul '13

Hi everyone, Every time I want to use an array in Haskell, I find myself having to look up in the doc how they are used, which exactly are the modules I have to import ... and I am a bit tired of staring at type signatures for 10 minutes to figure out how these arrays work every time I use them (It's even worse when you have to write the signatures). I wonder how other people perceive this issue and what possible solutions could be. Eg. look at the type signature for changing a single entry in an array: * vector package: write :: PrimMonad m => MVector (PrimState m) a -> Int -> a -> m () * array package: writeArray :: (MArray a e m, Ix i) => a i e -> i -> e -> m () * bytestring package: not available * a reasonable type signature would be: write :: MVector a -> Int -> a -> ST s a # To many different implementations Why do we need so many different implementations of the same thing? In the ghc libraries alone we have a vector, array and bytestring package all of which do the same thing, as demonstrated for instance by the vector-bytestring package. To make matters worse, the haskell 2010 standard has includes a watered down version of array. I personally prefer the vector package but if you want to use libraries for strings, I am forced back to use bytesting. And now that Array was added to haskell 2010, that will start to pop up more and more. The multitude of already existing libraries is also why I am writing this to haskell-cafe and not spinning yet another implementation. # Index I don't really see a reason for having an index of a type other than Int and that starts somewhere else than at 0. While there might be corner cases where such a thing might be useful, it is only confusing and irritating for the (presumably) rest of us. # Storable vs Unboxed Is there really a difference between Storable and Unboxed arrays and if so can't this be fixed in the complier rather than having to expose this problem to the programmer? # ST s vs IO This is probably the hardest to resolve issue. The easiest solution is probably to just have a module for each of them as in the array package. I find the PrimState a bit complicated and circuitous. The ideal solution would be to have type IO a = ST RealWorld# a in the next haskell standard. If I understand it correctly this would let you declare the types as follows but and still use it in an IO context. write :: MVector a -> Int -> a -> ST s a Would this work? I know it would probably screw up all instances instance ... IO where On the other hand, this is not only an issue with arrays but all procedurally accelerated data structures like hash-tables. Silvio

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