May 2011 - web-devel - Haskell.org

Hamlet , pattern matching
by Anton Cheshkov 16 May '11

16 May '11

Hi Michael, I can suggest Hamlet does not support pattern matching like: *$forall ((orderKey, order), (offerKey, offer), mbFeedback) <- results* * * It would be extremely convenient to have this functionality . Maybe there is another simple way to walk through list like [(a,b,c)] in Hamlet ? Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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Yesod i18n: Likely some breaking changes coming
by Michael Snoyman 15 May '11

15 May '11

Hi all, In the most recent releases of Hamlet and yesod-core, I added some of the i18n code. I'd like to clarify that this stuff should be considered experimental until the 0.9 release, and I will likely be releasing some breaking changes in the 0.8.* series. If you're building your production site off of this code, either (1) speak up now or (2) put in very strict version bounds. Michael

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Generic string interpolation library
by vagif.verdi＠gmail.com 15 May '11

15 May '11

Currently i use interpolatedstring-perl6 library for string interpolations (sql statements etc) But i remember there were discussions on including such generic string templates into yesod. It would be good to get rid of another dependency. What is the status of it ? Regards, Vagif Verdi

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Hamlet syntax suggestion
by Neil Mitchell 15 May '11

15 May '11

Hi, I am thinking of doing a project using Hamlet (and perhaps a little of Yesod, I'm not quite sure). As I was reading through the book (excellent resource!) I was surprised by the syntax for $maybe, in particular that you get case matching on only the Maybe type. Being used to Haskell I'm a fan of general solutions, so I commented on the book (http://www.yesodweb.com/book/templates#c5) Since book comments aren't really the right place to discuss something technical I thought I'd move it here. Currently Hamlet has: $if a; $elseif b; $else $maybe x <- ma; $nothing I think if $if was expanded to be pattern guards, rather than boolean expressions, it would be more powerful, yet remain just as easy to use. So, I'd like: $if Just x <- ma To be equivalent to: $maybe x <- ma Then $else and $nothing also become equivalent. If you also allow commas you can write things like: $if Just x <- age, x > 18 adults $else kids These have a very simple explanation - they're just pattern guards. Michael wants Hamlet to remain simple, in order to allow designers to use it without knowing programming. I think that's a reasonable goal, but I don't think a richer syntax for $if would make it any harder in the common case. I also think that if inexperienced people have to do more advanced tricks - i.e. converting their ADT into nested Maybe values in order to do some case analysis, it's going to end up harder in the long run. I had two other, smaller thoughts, while reading the book: 1) $for x <- xs, x > 12 could be used to generalise $for to list comps. However, I notice you've got $for working over anything Foldable, rather than just lists, so it's not necessarily such a clear conversion. It's probably also less useful - since filter isn't too bad - and you can always do $for x <- [x | x <- xs, x > 12] 2) CoffeeScript makes Javascript much more useful. It would be very cool if as well as Julius there was something more like CoffeeScript, or perhaps exactly CoffeeScript. I also idly wondered if you could translate Haskell syntax to Javascript (without the types), but perhaps that isn't such a great idea. Thanks, Neil

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Yesod. Persistent. The little problem
by Anton Cheshkov 12 May '11

12 May '11

Hi All, i have the difficulty to build query kind of *select * from Table T where T.f1 = v1 and (T.f2 = v2 or T.f3 = v2) * how to make this one with Yesod Persistent. Are there any ideas ? Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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Deploying a yesod app to production, without compiling in production servers.
by Nubis 12 May '11

12 May '11

Hi guys, After lots of effort, the yesod app I'm working on is finally ready to be deployed in a production environment, but I'm having a hard time deciding what's the best strategy to do so. I have proper development, staging and production environments. We'll be doing our coding on development, then tag a revision and push it to staging, and then if everything works fine we'll push that same tag to production. We're going to be using ubuntu 11.04 and all machines will be the same architecture too. My main concern is that compiling in production may be inefficient and badly stress the server, so these are my deployment options so far, I would like to hear your opinions on them, and maybe you can also answer some of the questions that arise from them: * Compile and statically link the app, then push it to staging, and if it works, to production: Would be great, but I'm getting some warnings relating glibc and errors linking libgss which I could fix, but hint's that It's going to be painful to keep a statically linked version and suggest it's going to be brittle. * Compile and move the binary and all the libraries it uses to the server: In theory it should work, but I'm not sure which libraries or library directories I should move/rsync. I'm also worried this way of doing it could be brittle since I could add dependencies that install stuff in different places and forget to add them which would mess up my deployment process a bit and require further manual intervention. * Compile on the server: It's really convenient since I could copy the source to the server and do a cabal-install there, but I'm afraid it will stress the server too much while compiling (granted, won't be often on production), but also keeping ghc and cabal on the server requires the extra work of keeping them up to date in an unobtrusive fashion. I tend to break my ghc install rather frequently, I wouldn't like to find myself logging in to production to fix a broken ghc/cabal/haskell platform install. Thanks for your advice, also let me know if you think I'm too much of a slacker, unlucky, or worrying too much about nothing. cheers ----nubis :)

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yesod build failure on Mac
by Mark Wotton 12 May '11

12 May '11

cabal install yesod fails because certificate-0.9.0 won't build on Mac. -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda

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How to expire session when browser is closed ?
by vagif.verdi＠gmail.com 12 May '11

12 May '11

Currently yesod provides clientSessionDuration settings. But i want to change it to expire session when browser is closed. How do i do that ? Regards, Vagif Verdi

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Message is not generated.
by vagif.verdi＠gmail.com 10 May '11

10 May '11

Yesod application runs fine on my dev pc, and shows message on html page (getMessage) after post-redirect. Same application moved to test env, works fine but does not show the message. The html page has everything except the message. I installed and reinstalled yesod and all libraries from scratch, removed all tmp files from static folder. Regards, Vagif Verdi

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Installing yesod with cabal
by Anakreon 10 May '11

10 May '11

Installation of yesod fails because the package language-javascript-0.4.4 fails to install. It requires happy although happy-1.18.6 is successfully installed with cabal. The operating system is linux with debian sid and ghc version 6.12.1, cabal-install version 0.8.2 using version 1.8.0.2 of the Cabal library. I searched for a google group on yesod and didn't find any. Except for this mailing list, is there any other way to seek help from the yesod community?

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