- Beginners - Haskell.org

Re: [Haskell-beginners] list problem
by Tyler Huffman 03 Mar '14

03 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 03 Mar '14

03 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 02 Mar '14

02 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 28 Feb '14

28 Feb '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 27 Feb '14

27 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 26 Feb '14

26 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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Re: [Haskell-beginners] Beginners Digest, Vol 68, Issue 23
by Patrick Lynch 25 Feb '14

25 Feb '14

Good morning, Re: Today's Topic 1 - see below. My apology for not including the error message. The following is what I did: I downloaded the source code and did the following [from the O'Reilly book]: 1. download was done on a Mac. 2. I saved the file to helloWorld.hs 3. I went to my terminal screen and executed: runhaskell helloworld.hs 4. on the terminal the following appeared: hell yeah 5. so far, so good 6. I went to my browser and entered the url: http://localhost:3000 7. I was expecting to see the following on my browser: <!DOCTYPE html> <html><head><title></head><body>hell yeah</body></html> 8. Unfortunately, I get the following message: "Safari can't connect to Server Safari can't open page "http://localhost:3000" because Safari can't connect to server "localhost" Good day, Patrick ----- Original Message ----- From: <beginners-request(a)haskell.org> To: <beginners(a)haskell.org> Sent: Tuesday, February 25, 2014 7:00 AM Subject: Beginners Digest, Vol 68, Issue 23 > Send Beginners mailing list submissions to > beginners(a)haskell.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://www.haskell.org/mailman/listinfo/beginners > or, via email, send a message with subject or body 'help' to > beginners-request(a)haskell.org > > You can reach the person managing the list at > beginners-owner(a)haskell.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Beginners digest..." > > > Today's Topics: > > 1. Re: Beginners Digest, Vol 68, Issue 22 (KMandPJLynch) > 2. Re: Beginners Digest, Vol 68, Issue 22 (Mateusz Kowalczyk) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Mon, 24 Feb 2014 20:32:40 -0500 > From: KMandPJLynch <kmandpjlynch(a)verizon.net> > To: beginners(a)haskell.org > Subject: Re: [Haskell-beginners] Beginners Digest, Vol 68, Issue 22 > Message-ID: <609E40BD-3267-4F21-88A6-1BDC4DEDC609(a)verizon.net> > Content-Type: text/plain; charset=us-ascii > > Good evening, > > I'm trying to learn how to implement Haskell on a web site. > I've got the O'Reilly book: "Developing Web Applications with Haskell and > Yesod". > I'd appreciate some guidance in regard to this. > I'm having a bit of a problem getting the helloWorld.hs app up and running > on Yesod. > > Thank you > > On Feb 24, 2014, at 2:30 PM, beginners-request(a)haskell.org wrote: > >> Send Beginners mailing list submissions to >> beginners(a)haskell.org >> >> To subscribe or unsubscribe via the World Wide Web, visit >> http://www.haskell.org/mailman/listinfo/beginners >> or, via email, send a message with subject or body 'help' to >> beginners-request(a)haskell.org >> >> You can reach the person managing the list at >> beginners-owner(a)haskell.org >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of Beginners digest..." >> >> >> Today's Topics: >> >> 1. Failure to install cabal-install. (Derek Mahar) >> 2. Re: Failure to install cabal-install. (Derek Mahar) >> >> >> ---------------------------------------------------------------------- >> >> Message: 1 >> Date: Mon, 24 Feb 2014 13:20:45 -0500 >> From: Derek Mahar <derek.mahar(a)gmail.com> >> To: beginners(a)haskell.org >> Subject: [Haskell-beginners] Failure to install cabal-install. >> Message-ID: >> <CABtfiZb7+p=DtGoz57GVXwgHCdK1vPL175UxmirRY1EXM4aEBA(a)mail.gmail.com> >> Content-Type: text/plain; charset="utf-8" >> >> 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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