September 2010 - Haskell-Cafe

variable definition according to input
by Maria Merit 05 Sep '10

05 Sep '10

Hello, Is it possible to define variable names according to input data? For instance: input = "I k" => Int k input = "I m" => Int m input = "S s" => String s Of course, the real application is much more complicated, but the basic question is the same. Many thanks, Maria

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ANNOUNCE: darcs 2.5 beta 5
by Reinier Lamers 05 Sep '10

05 Sep '10

The darcs team would like to announce the immediate availability of darcs 2.5 beta 5 (also known as darcs 2.4.98.5 due to Cabal restrictions). Important changes since darcs 2.4.4 are: * trackdown can now do binary search with the --bisect option * darcs always stores patch metadata encoded with UTF-8 * diff now supports the --index option * amend-record now supports the --ask-deps option * apply now supports the --match option * amend-record has a new --keep-date option * inventory-changing commands (like record and pull) now operate in constant time with respect to the number of patches in the repository * the push, pull, send and fetch commands no longer set the default repository by default * the --edit-description option is now on by default for the send command Changes since the last beta release are: * document that GHC 6.10 is required to build darcs 2.5 * the --index flag is now disabled for amend-record because it was broken * clean up documentation for trackdown * no longer require a specific version of the hashed-storage package If you have installed the Haskell Platform or cabal-install, you can install this beta release by doing: $ cabal update $ cabal install darcs-beta Alternatively, you can download the tarball from http://darcs.net/releases/darcs-2.4.98.5.tar.gz and build it by hand as explained in the README file. Kind Regards, the darcs release manager, Reinier Lamers

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Re: [Haskell-cafe] Announce: lhae
by abau＠imn.htwk-leipzig.de 05 Sep '10

05 Sep '10

> Seems cool, but I do not really get it : why write it in haskell ? I > thought at first that your "formula language" was haskell, but it > looks more like a php derivative. This "formula language" is just a very simple language to insert formulas into cells. It has nothing to do with haskell. > Does it do more than the spreadsheet thing in openoffice ? I don't know the spreadsheet in openoffice, but I don't think that lhae does anything more or better than openoffice. > Also, maybe you could do the same with gnuplot, it would be really > cool to be able to use a friendlier language for defining functions > other than polynomials or the few standard floating point functions. Sorry, but I don't understand this point. I thought gnuplot is just for plotting graphs. But lhae is a (low level) spreadsheet application. But I may got something wrong on your question? _____________________________________________ HTWK Leipzig FIMN Webmail https://webmail.imn.htwk-leipzig.de/nocc/

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Re: [Haskell-cafe] Announce: lhae
by abau＠imn.htwk-leipzig.de 05 Sep '10

05 Sep '10

Serguey Zefirov <sergueyz(a)gmail.com> wrote: > You had selected wxWidgets because of what? Because of the neat grid class in wxWidgets. I did not find anything comparable in gtk. > Also, how long did it took (especially GUI part)? Hard to say, because I work on that project on irregular times in my spare time. But the GUI part was not the big deal, because wxhaskell is such a handy library. [1] http://docs.wxwidgets.org/stable/wx_wxgrid.html _____________________________________________ HTWK Leipzig FIMN Webmail https://webmail.imn.htwk-leipzig.de/nocc/

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autocomplete using hoogle
by Yuras Shumovich 05 Sep '10

05 Sep '10

Hello, Just want to share some results of my weekend hacking. It is clear that haskell type checker can help to build a list of suggestions for autocomplete (very old idea). I tried to create a very basic prototype to play with the idea. The approach I used: The task can be divided into the next two parts: - find the most general type of the word we are trying to complete that will satisfy the type checker - find all the symbols that "match" the found type The first task can be solved using ghc. Just replace the word with "()" and ghc will tell you something like Couldn't match expected type `m String' against inferred type `()' The second task can be solved using hoogle. Just ask it to find everything that matches "base :: type", where base -- already known part of the word; type -- the type that ghc expects. Source code is attached (linux only at a moment) haskell.vim -- very basic ftplugin for vim Place it into your ~/.vim/ftplugin directory (don't forget to backup an existent file if any) complete.hs -- simple script that does actual work. How to use it. cd to the cabal package you are working on at a moment mkdir dist/hscomplete copy complete.hs file to the dist/hscomplete edit complete.hs (at least change the package name, it is hard coded) create hoogle database for your package: cabal haddock --hoogle hoogle --convert=dist/doc/html/<packageName>/<packageName>.hoo +base +directory +... (all packages you depend on) start vim (you should be in the directory where <package>.cabal file is placed!) Use C-X C-O to auto complete Example: cabalized package "tmp" contains two modules Data.Tmp and Data.Tmp1 Data.Tmp1 imports Data.Tmp Data/Tmp.hs contains veryLongLongName1 :: Int veryLongLongName1 = 1 veryLongLongName2 :: Char veryLongLongName2 = 'c' veryLongLongName3 :: String veryLongLongName3 = "Hello" vim src/Data/Tmp1.hs import Data.Tmp tmp1 :: Monad m => [a] -> m Int tmp1 a = very<C-x C-O> suggests veryLongLongName1 tmp2 :: Monad m => [a] -> m Char tmp2 a = very<C-x C-O> suggests veryLongLongName2 and veryLongLongName3 tmp3 :: Monad m => [a] -> m String tmp3 a = very<C-x C-O> suggests veryLongLongName3 Warning: not ready for real use (no error handling, a lot of hard codes, slow, etc). Just for playing Yuras

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Crypto-API is stabilizing
by Thomas DuBuisson 05 Sep '10

05 Sep '10

All, Crypto-API - a unified interface to which I hope hash and cipher algorithms will adhere - has recently gotten a reasonable amount of polish work. I continue to welcome all comments! A blog on its current interface is online [1] as are darcs repositories of the crypto-api package [2]. Recent changes includes added block cipher modes, platform-independent RNG, tests, a simplistic benchmark framework, and minor tweaks of the classes. I've made experimental hash, block cipher and stream cipher instances. Almost no optimizations have been made as of yet! Thanks to everyone for their past comments! I have made numerous changes based on input received. If you feel I didn't respond properly to your suggestion then please ping me again - this is purely a spare time effort and things do fall through the cracks. Cheers, Thomas [1] http://tommd.wordpress.com/2010/08/23/a-haskell-api-for-cryptographic-algor… [2] http://community.haskell.org/~tommd/crypto/ (If you're wondering why you're BCCed its probably because you worked on a crypto-related Haskell package)

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help me evangelize haskell
by Leonel Fonseca 04 Sep '10

04 Sep '10

Michael: Hi. I take the risk to mention some facts you might already be working on. I speculate on three perceptions in the mind of decision makers related to the adoption of a new language in a shop. This perceptions can be modified in stages. First Stage: Awareness. Why programming in that language matters? Once you can justified this, advance to the following stage. Haskell is nice, quick to develop, brings tools to make abstractions at any level and has tools and libraries. And community support is really awesome! If you invest more in learning, you can strive to use it as formal programming method and earn safety guarantees. Please, see elsewere for success stories that help you to motivate and encourage management to test the new alternative. Second Stage: Small term engagment. Why your shop should do little investment in trying a new language in a small but representative project? Here you can make two arguments to gain support in this stage: 2.A) The shortcommings of the current tools/languages. 2.B) Small concept programs of how your current language/tool would fail where the new one would success. You can gain credibility by showing how your new tool could be short on some aspect that it's well mastered in the old one. (i.e. be impartial). Someone has already pointed how fragile interpreted programs are. In this stage you must gain both decision makers and peers recognition of the problem the shop is facing with the current language versus the improvements of using the new language. A project must be acomplished and reviewed, so a decision can be made over the facts of costs and benefits. Third Stage: Adoption. Is it really better to adopt a new language? At this point you have evidence of possible benefits and costs. And a decision is made. Among other costs, please take in account that embracing any new language in a shop will require formalised (funded, time alloted to, machines, any other resource) learning and coaching activities. Haskell has long learning curve. And you must consider this cost of being less productive than in your current language. There's too the risk of hitting walls in a tight-schedule situation. You can lower this risk of failure if you arrange to have a mentor (master) who can lead, provide hints to co-workers, discuss approaches and solve hard issues whenever they appear. Counter-arguments that you must deal with: c1) Why not... Erlang? F#? See Jon Harrop's claims. Scala or Clojure? c2) Performance predictability. c3) On the fly script generation and execution. c4) Will your co-workers be happy of embracing a new paradigm of solving problems? Will type signatures appear as pain or a valuable thing to them? -- Leonel Fonseca.

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Why does ghci recompile the module compiled in different OS ?
by zaxis 04 Sep '10

04 Sep '10

Both linux and freebsd has the same .ghci file. >cat ~/.ghci :def hoogle \str -> return $ ":! hoogle --count=15 \"" ++ str ++ "\"" :cd /media/G/www/qachina/db/doc/money the money.hs has many functions i need to use. On freebsd, i use the following command to compile it: >ghc -c -O2 money.hs >ls Money.hi Money.hs Money.o When entering ghci, it indeed doesnot recompile the module. >ghci ... Ok, modules loaded: Money However, when i use the same module in archlinux, the ghci does recompile the module: >ghci ... [1 of 1] Compiling Money ( Money.hs, interpreted ) Ok, modules loaded: Money. Any suggestion is appreciated! ----- e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-does-ghci-recompile-the-module-compiled-in-differ… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Platform on Windows - cabal update problems.
by Serguey Zefirov 04 Sep '10

04 Sep '10

I've installed recent Haskell Platform and tried to wrap my head around cabal to finally figure out how to use it. First thing I bumped into is that cabal.exe does not know about any remote repositories, even about hackage. So after googling I found that I should add a line "remote-repo: hackage.haskell.org:http://hackage.haskell.org/packages/archive" into my cabal config file. So I did. And now I have "cabal update" command trying to download packages list from hackage. To no avail. Now it gives me even more interesting error: "cabal.EXE: fromFlag NoFlag. Use fromFlagOrDefault" Googling doesn't help here. What does it mean and how to get rid of it?

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New .hs File Icons
by Christian Eltges 04 Sep '10

04 Sep '10

Hello, I was wondering why the File-Icon installed by GHC with the lambda for .hs files hasn't changed to the new bind+lambda icon used on haskel.org. Is this because it should be the same as the icon used by hugs? I've created a new icon myself, which I use on my pc (using the svg file from the haskell wiki). So if the only reason for using the old icon was, that there is no new one, then you can use this. Best regards Christian

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