- Beginners - Haskell.org

"Developing Web Applications with Haskell and Yesod"
by KMandPJLynch 04 Mar '14

04 Mar '14

I'm reading the O'Reilly book "Developing Web Applications with Haskell and Yesod" but can't get the helloworld.hs app, from the book, to work. This is what I did: 1. I downloaded Haskell and it works just fine. 2. cabal update 3. cabal install yesod 4. I downloaded the helloworld.hs program - see following: {-# LANGUAGE TypeFamilies, QuasiQuotes, MultiParamTypeClasses, TemplateHaskell, OverloadedStrings #-} import Yesod data HelloWorld = HelloWorld mkYesod "HelloWorld" [parseRoutes] / HomeR Get|] instance Yesod HelloWorld getHomeR :: Handler RepHtml getHomeR = defaultLayout [whamlet[|Hell World!|] main :: IO () main = warpDebug 3000 HelloWorld 5. I went to the terminal on a Mac and entered command: runhaskell helloworld.hs 6. on the terminal the following is displayed: Hell World! 7. I opened a Safari browser and entered: http://localhost:3000 8. the following error message is displayed: "Safari can't connect to Server. Safari can't open the page http://localhost:3000/ because Safari can't connect to localhost" I'd appreciate any help.

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Re: [Haskell-beginners] list problem
by Tyler Huffman 04 Mar '14

04 Mar '14

I would definitely recommend the #haskell IRC channel for simple questions as well. Usually they're better at less complicated questions than the Haskell Beginner mailing list. Here's a link for some more information: ( http://www.haskell.org/haskellwiki/IRC_channel) Best of luck! On Mon, Mar 3, 2014 at 10:40 AM, Emanuel Koczwara <poczta(a)emanuelkoczwara.pl > wrote: > Hi, > > W dniu 03.03.2014 18:04, Roelof Wobben pisze: > > I am studing this by following the wiki tutorial and then the Haskell > basic tutorial. > But if you have a better tutorial I'm happy to study this one too. > > Roelof > > > > Benjamin Edwards schreef op 3-3-2014 17:59: > > The problem is that you don't seem to understand how singly linked lists > work. I would recommend studying this first, then understanding how to > append a value to the end of the list in haskell will probably make a lot > more sense. > > >> > > This is of course mailing list for beginners and we are happy to help > you, but your questions are _very_ basic. Please take a look at > http://learnyouahaskell.com. > > Regards, > Emanuel > > > _______________________________________________ > Beginners mailing list > Beginners(a)haskell.org > http://www.haskell.org/mailman/listinfo/beginners > > Regards, Tyler Huffman

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list problem
by Roelof Wobben 04 Mar '14

04 Mar '14

Hello, I have this : cons8 n l = n : l x = cons8 8 [1,2,3] main = print x This will be the output: [8.1.2.3] Now the problem is how I can take care that the output will be [1,2,3,4,8] I have to change the function for it. I tried switching n and L in the function but that will not work. Or does I have to do x = cons [1,2,3] 8 and make the function like this cons8 l n = l : n Roelof --- Dit e-mailbericht bevat geen virussen en malware omdat avast! Antivirus-bescherming actief is. http://www.avast.com

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foldr problem
by Roelof Wobben 03 Mar '14

03 Mar '14

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Question about Ord for lists and multi-dimensional lists
by Tyler Huffman 03 Mar '14

03 Mar '14

Hi all, I'm having trouble finding resources explaining how Ord for two lists works. I've created a public gist to explain what I mean. https://gist.github.com/iduhetonas/9318958 Could anybody shed some light on what I'm seeing? Regards, Tyler Huffman

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where do i get wrong
by Roelof Wobben 03 Mar '14

03 Mar '14

Hello, I try to selfstudy haskell by following the yet another haskell tutorial. Now I have the exercise where I have a string and have to convert it into a list of Booleans based on lower cats letter using map. So i tried this x = "aBCde".islower:[] But I see this error : Not in Scope: 'isLower'. Where do I make my error. Do not give the answer otherwise I do not learn anything from it. Roelof --- Dit e-mailbericht bevat geen virussen en malware omdat avast! Antivirus-bescherming actief is. http://www.avast.com

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web client/server app - what to choose
by Miroslav Karpis 01 Mar '14

01 Mar '14

Hi, please can you help me with following: I would like to make a server/client web app, but I'm not sure what packages/modules would do the best. I did several client/server applications not in Haskell, where I have used REST (JSON) API as a communication between client and server. In Haskell I'm not sure what would be best, but for future use most probably also REST/JSON would be best. Server will do some realtime mathematical calculations . After its done it will send to client results. Client will visualize the results via WebGL/Threejs. I was thinking about Snap for server but for client I'm not really not sure. Any ideas/comments more than appreciated ;-) Cheers, M.

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Cabal update possible?
by Obscaenvs 28 Feb '14

28 Feb '14

Have: * The Glorious Glasgow Haskell Compilation System, version 7.6.3 * cabal-install version 1.16.0.2 using version 1.16.0 of the Cabal library Can I update to Cabal 1.18 so I can use sandboxes without breaking my dependencies? I think that that is what broke my Haskell toolchain 2h ago. Now I redid it so everything's fine, but I'd like to use sandboxes. If impossible, hsenv has worked for me in the past, but... I did not want to use Haskell Platform, since it pulls in several OpenGL libs completely unnecessary *for* and potentially detrimental *to* my server. "Haskell Platform, Server Edition", anyone? fredrik

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Failure to install cabal-install.
by Derek Mahar 27 Feb '14

27 Feb '14

How can I tell the Haskell compiler where to find module Control.Monad.Error? After building GHC 7.6.3 and Haskell Platform 2013.2 on Red Hat Linux 6, I found that 'cabal install cabal-install' fails when it attempts to build library HTTP-4000.2.11 because the Haskell compiler cannot find module Control.Monad.Error. ******************************************************* * Installation completed successfully. * * Programs installed into: * /usr/local/bin * * Now do "cabal update" to initialize the package list * * Additional packages may be found at http://hackage.haskell.org * or via "cabal list <pattern>" * * Use "cabal install <foo>" to install additional packages * ******************************************************* [dmahar@dmahar haskell-platform-2013.2.0.0]$ cabal update Downloading the latest package list from hackage.haskell.org Note: there is a new version of cabal-install available. To upgrade, run: cabal install cabal-install [dmahar@dmahar haskell-platform-2013.2.0.0]$ cabal install cabal-install Resolving dependencies... Configuring HTTP-4000.2.11... Building HTTP-4000.2.11... Preprocessing library HTTP-4000.2.11... Network/Stream.hs:35:8: Could not find module `Control.Monad.Error' There are files missing in the `mtl-2.1.2' package, try running 'ghc-pkg check'. Use -v to see a list of the files searched for. Failed to install HTTP-4000.2.11 cabal: Error: some packages failed to install: HTTP-4000.2.11 failed during the building phase. The exception was: ExitFailure 1 cabal-install-1.18.0.2 depends on HTTP-4000.2.11 which failed to install. Thank you, Derek

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copy file and create directory
by Renah Scarowsky 26 Feb '14

26 Feb '14

Is there a version of copyFile that will create the directory structure if it does not exist yet? Thanks, Renah Scarowsky Suite Solutions Create>Manage>Deploy http://www.suite-sol.com<http://www.suite-sol.com/>

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