- web-devel - Haskell.org

real Models in Yesod
by Greg Weber 15 Jul '11

15 Jul '11

Yesod (and AFAIK other haskell frameworks) do not have strong models. In my experience, the heart of an individual model is validation logic. One can achieve validation by writing their own save function, however this allows multiple possible entries into saving a model because they can write multiple different save functions. Real enforcement of a single entry point with triggers is possible in TCache [1] where triggers are tied into the persistence layer. The main other issue I see causing weak models is the separation of forms from models. So I want to propose a design for stronger models and see what critiques and better ideas there are. Lets start with a data structure for a model: Person { personAge :: Int, personSex :: Maybe String } The main aspect is the addition of triggers, which are callbacks ran before a save to the database. A trigger is either a validator or a modifier. A validator is run as a callback before a save to the database. myTrigger :: Person -> Either ValidateError Person A ValidationError will be associated with a particular model, and possibly with a particular field of that model. We may want a validation errors to stop any more validations from being ran, or we may want to run all validations (just as a form returns all errors, not just one). ValidationError = FieldInvalid EntityField Text | BaseInvalid Text | ShortCircuitValidation ValidationError verifySex :: Person -> Either ValidationError Person verifySex p = when ((personAge p) > 18 && isNothing (personSex p)) FieldInvalid PersonSex "is required" return p Note that this is a non-monadic trigger, but triggers do need the ability to run database queries. One approach to registering callbacks would be to place them in the schema. Person triggers=verifySex, trigger2, trigger3 age Int sex String Maybe So now we can have a save function. ModelSave val = ModelValid val | ModelInvalid val [ValidationError] save :: val -> ModelSave val sav <- savePerson person case sav of ModelValid person -> ModelInvalid (person, errors) -> Note that both Constructors have a person. This is to allow triggers to modify the person. Now we need a technique for tieing the model to the form. I will use some magical functions. getNewPerson = do f <- newPersonForm [|hamlet| ^{f} |] postCreatePerson = do res <- saveForm personForm case res of ModelValid person -> ... ModelInvalid (person, errors) -> editPersonFrom person errors [1] http://hackage.haskell.org/packages/archive/TCache/0.8.0.2/doc/html/Data-TC…

4 5

Pre-announcing: a HTTP load tester
by Bryan O'Sullivan 14 Jul '11

14 Jul '11

Hi, folks - I'm currently working on a Haskell-based HTTP load tester, as I've gotten tired of fighting with apachebench and httperf. While there's no release yet, the code as it currently stands does work, and it prints statistics about what it has measured. I'm announcing it long before it's ready for prime time because I think others within this community might already find it useful even in its current rough form, and because I'd love to solicit patches and feature requests from you. The current code base is small enough that it's really easy to hack on. https://github.com/mailrank/http-load-tester

2 1

yesod devel alternatives for sandbox environment
by Eric Rasmussen 13 Jul '11

13 Jul '11

Hi everyone, I'm looking to get started with Yesod for the first time and need some guidance. I installed Yesod with cabal-dev (which I needed to resolve some of the dependency conflicts), and then discovered/read that I won't be able to use the yesod devel server with a sandbox environment. I read some old discussions on the list saying this is being worked on, but in the meantime what other options do I have? Since I'm completely new to Haskell web development I'm not sure if I should be looking into warp-debug or something else as a reasonably easy way to test an application under development. I'm definitely open to any advice or other tips and tricks on setting up a nice development environment for Yesod. Thanks! Eric

2 3

Request for help on haskellers.com
by Michael Snoyman 13 Jul '11

13 Jul '11

Hi all, Since writing haskellers.com, I haven't had very much time to add new features to it, which I'm sure many people were hoping for. So I wanted to turn to the web-devel community for some assistance: is there anyone out there who would like to take a crack at some new feature they've been missing? You'll get to (1) give back to the Haskell community, (2) get some experience on a real-world Yesod site and (3) get your name attached to said site. If anyone's interested, let me know. The code is all available on Github[1], so feel free to fork and send a pull request as well. I guess now's also a good time to ask which features people have been missing the most, in the hopes that someone else will write it for me ;). Michael [1] https://github.com/snoyberg/haskellers

1 0

JS caching
by Mister Asafe Ribeiro 12 Jul '11

12 Jul '11

Suppose I want to avoid caching of my js files. I did something like that: script ! type_ "text/javascript" $ getScripts [my,editJS] Where my = "document.write('<script type=\"text/javascript\" src=\"/js/my.js?' + new Date().getTime() + '\" ><\\/script>');" booksJS = "document.write('<script type=\"text/javascript\" src=\"/js/books.js?' + new Date().getTime() + '\" ><\\/script>');" getScripts scripts =preEscapedString $ foldl1 (++) scripts Although I load the scripts, it seems I'm not avoid anything at all. What is the better (or right way) to do that (with Happstack and blaze-html)?

1 0

web-routes documentation and blogpost now available
by Jeremy Shaw 11 Jul '11

11 Jul '11

Hello, I have just published a blog post and tutorial on using web-routes: http://happstack.blogspot.com/2011/07/type-safe-urls-via-web-parts-part-1.h… http://happstack.com/docs/crashcourse/WebRoutes.html web-routes provides type-safe URL routing. It is not tied to any particular web-framework or templating library. So, if you are interested in type-safe urls, I encourage you to give it a look. If you are not interested in type-safe urls.. you should be ;) Additional documentation/tutorials is planned. - jeremy

1 0

[ Yesod ][ Newbie ][ Widgets ] Ways of adding app manu
by Kamil Ciemniewski 08 Jul '11

08 Jul '11

Hi all, I'm trying to add to my "admin layout" main menu in Yesod. Normally - doing it in Rails - I would create a partial or helper and then use it in my layout file. But here in Yesod - the concept of widgets seems somewhat fereign to me. I don't quite get them. In my Handler.Admin module I define: adminLayout :: GWidget MyApp MyApp () -> GHandler MyApp MyApp RepHtml adminLayout widget = do mmsg <- getMessage mroute <- getCurrentRoute pc <- widgetToPageContent $ do widget hamletToRepHtml $(hamletFile "admin/admin-layout") then I define my widget ( all in the same file ): mainMenu :: Widget () mainMenu = addWidget $(widgetFile "admin/_menu") And finally in "admin/admin-layout.hamlet" I'm trying to render my menu: ... ^{mainMenu} ... All without a luck.. Compiler yells at me strange ( to me ) things: Handler/Admin.hs:31:27: Couldn't match expected type `GGWidget MyApp (GHandler MyApp MyApp) ()' with actual type `(url0 -> [(T.Text, T.Text)] -> T.Text) -> blaze-html-0.4.1.1:Text.Blaze.Internal.Html' Expected type: Widget () Actual type: hamlet-0.8.1:Text.Hamlet.Quasi.Hamlet url0 In the return type of a call of `pageBody' In the first argument of `hamlet-0.8.1:Text.Hamlet.Quasi.fromHamletValue', namely `pageBody pc' Which doesn't occur when I'm not trying to render "mainMenu" widget. What am I doing wrong? And are there any informations about using widgets anywhere? ( because I haven't found many.. )? Best regards Kamil Ciemniewski

2 1

Haskell code highlighting
by Michael Snoyman 08 Jul '11

08 Jul '11

Hi all, I want to add (back) Haskell code highlighting to the Yesod site, and decided to take a poll for what package people recommend. A quick browsing of Hackage reveals the following possibilities: * http://hackage.haskell.org/package/colorize-haskell * http://hackage.haskell.org/package/highlighter * http://hackage.haskell.org/package/highlighting-kate * http://hackage.haskell.org/package/hscolour What do people recommend? And what are people's preferred CSS file for this? Thanks, Michael

3 3

[yesod] Messages / i18n question: how to handle "xx-xx" languages
by Markus Barenhoff 08 Jul '11

08 Jul '11

Hi! I'am using mkMessage to create the i18n stuff for a project. I've created a en.msg and a de.msg and everything is running smoothly and I can use the message consts in my hamlet template with _{}. But I'am a little bit unsure whats the best practise to handle the language parameters like 'de-de' or 'en-us'. The Message framework does not seem to handle those cases by using en.msg for en-us if en-us.msg is not found. But copying the message files also seems not a good option. Putting a "take 2" version of the language to the _LANG cookie var works, but needs a reload to become active... Any suggestions / best practice advices? Regards Markus

2 3

[yesod] how convert Content to String or Text
by Dmitriy Nikitinskiy 07 Jul '11

07 Jul '11

Hello All. I have following code: getMyRoute :: String -> Handler RepXml getMyRoute r = liftM RepXml $ hamletToContent [hamlet|<node |] getOtherRoute :: Handler () getOtherRoute = do (RepXml mycontent) <- getMyRoute "something" -- how write mycontent to file here? -- let str = ???? or str <- ???? -- liftIO $ writeFile "myfile.xml" str return () How convert Yesod.Content.Content to String or Text? Thanks. Dmitriy

2 2