- web-devel - Haskell.org

Exception Handling on GHandler monad level
by Anton Cheshkov 17 May '11

17 May '11

Hi Michael, i need to handle exception on GHandler monad level. We have: *type GHandler sub master = GGHandler<http://hackage.haskell.org/packages/archive/yesod-core/0.8.1/doc/html/Yesod…> sub master (Iteratee<http://hackage.haskell.org/packages/archive/enumerator/0.4.10/doc/html/Data…> ByteString<http://hackage.haskell.org/packages/archive/bytestring/0.9.1.10/doc/html/Da…> IO<http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/System-IO…> **)* * *data GGHandler sub master m a ... MonadControlIO<http://hackage.haskell.org/packages/archive/monad-control/0.2.0.1/doc/html/…> m => MonadControlIO<http://hackage.haskell.org/packages/archive/monad-control/0.2.0.1/doc/html/…> (GGHandler<http://hackage.haskell.org/packages/archive/yesod-core/0.8.1/doc/html/Yesod…> sub master m) *(Iteratee<http://hackage.haskell.org/packages/archive/enumerator/0.4.10/doc/html/Data…> ByteString<http://hackage.haskell.org/packages/archive/bytestring/0.9.1.10/doc/html/Da…> IO<http://hackage.haskell.org/packages/archive/base/4.3.1.0/doc/html/System-IO…> **) have no instance of * MonadControlIO<http://hackage.haskell.org/packages/archive/monad-control/0.2.0.1/doc/html/…> thus we got error: No instance for (MonadControlIO (Data.Enumerator.Iteratee Data.ByteString.Internal.ByteString IO)) arising from a use of `E.catch' Possible fix: add an instance declaration for (MonadControlIO (Data.Enumerator.Iteratee Data.ByteString.Internal.ByteString IO)) i need something like: * * *function :: Handler (Maybe Int)* *function = do * * res <- E.catch (runDB $ do * * action1* * action2* * ... * * return 1* * )* * (\(e :: E.SomeException) -> return 0)* How i can get this ? Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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Yesod: facebook plugin
by Mathew de Detrich 17 May '11

17 May '11

I am currently transferring my website from using the client side flow version of facebook to using the server side flow (with the facebookauth helper) using Yesod and I am having issues getting the facebook plugin working. One of the interesting things I noticed is that the redirect_uri that Yesod outputs for my website is https://graph.facebook.com/oauth/authorize?client_id= <REMOVED>&redirect_uri=http%3a%2f%2flocalhost%2fauth%2fpage%2ffacebook&scope=userEmail%2cuserName%2cuserPasswordHash%2cuserCountryCode%2cuserActivated" Now the way I read this, the field in your facebook app should be localhost/auth/page/faceboook/ however putting this gives the error that redirect_uri is not the same as specified in the application, so I changed this to the same as the destination route which is defined in YesodAuth as loginDest _ = RootR (so in this case its just localhost), however when doing this I get an error (from facebook) stating "Invalid Arguments" (I retrieve a HTML page with the following in the body) <body><h1>Invalid Arguments</h1><ul><li>No input found</li></ul></body> Is there a trivial example lying around implementing simple facebook login using Yesod

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http-enumerator : Any way to get the headers first?
by Erik de Castro Lopo 16 May '11

16 May '11

Hi all, I'm continuing work on the HTTP proxy I'm writing. The absolute bare basics are working with Warp, Wai and http-enumerator as long as the upstream web server doesn't send gzipped or chunked data. For these later two cases, httpe-enumerator helpfully gunzips/unchunks the data. That however causes a problem. If my proxy simply passes the HTTP headers and data it gets from http-enumerator and passes then on to the client, the client barfs because the headers claim the data is gzipped or chunked and the data actually isn't chunked/gzipped. There are a number of possible solutions to this: a) Strip the content/transfer-encoding header and add a content-length header instead. I think this is probably possible with the API as it is, but I haven't figured out how yet. b) Rechunk or re-gzip the data. This seems rather wasteful of CPU resources. c) Modify the Network.Http.Enumerator.http function so that de-chunking/gunzipping is optional. d) Expose the iterHeaders function that is internal to the http-enumerator package so that client code can grab the headers before deciding how to handle the body. Are there any other options I haven't thought of yet? >From the options I have, I actually think d) makes the most sense, Would a patch exposing iterHeaders be accepted? Cheers, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Yesod: Lambda Abstraction inside interpolation
by Mathew de Detrich 16 May '11

16 May '11

I came across a situation where I tried using lambda abstraction inside variable/template interpolation (when adding html with hamlet) and found out that the quasi quoter inside hamlet had issues parsing lambda abstractions (I am assuming due to the use of the '\' character). Is there some way to do lamdba abstraction inside hamlet quasiquoter, and if not will there be support added for this? Thanks

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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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