March 2011 - web-devel

when we switch to aeson, perhaps a QQ for JSON..
by Max Cantor 09 May '11

09 May '11

I know that the kickass yesod team is looking to change the json library to aeson. One nice feature would be quasi-quoting for the library like in the following library. hackage.haskell.org/packages/archive/text-json-qq/0.2.0/doc/html/Text-JSON-…

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Last call for comments: WAI 0.4
by Michael Snoyman 01 Apr '11

01 Apr '11

Hi all, Just wanted to give everyone a last chance to give input on WAI 0.4 before its release. You can see the code on Github[1]. The main things to point out in this release are: * We've switched to using http-types, so WAI needs to define much less on its own (i.e., statuses, HTTP versions, etc). Additionally, we now rely on the case-insensitive library for header keys. * The Request datatype now contains parsed pathInfo and queryString. This makes it more efficient to write middlewares. The raw path info and query string are still available as rawPathInfo and rawQueryString, respectively. * Partial file responses are now supported. The ResponseFile constructor takes a fourth argument, Maybe FilePart. FilePart contains the offset and count. If anyone has other ideas that they'd like to see implemented in WAI, please get them in sooner, rather than later. I'm hoping that this release will last for quite a while. We'll also be releasing a number of associated packages at the same time (wai-extra, warp, wai-test, etc), so if you have comments on those, feel free to submit them as well. Michael [1] https://github.com/snoyberg/wai/blob/master/Network/Wai.hs

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Minor Yesod point release: worth the upgrade
by Michael Snoyman 31 Mar '11

31 Mar '11

Hi all, I've just released Yesod 0.7.3[1]. It's mostly just a matter of updating some dependencies to avoid bugs and performance leaks. So from that perspective, I recommend people upgrade at their earliest convenience. This release *does* offer one new feature: the "mini scaffolded site." Up until now, the yesod scaffolder always created full-featured sites, complete with authentication and persistence. You now have the choice of getting a minimalistic scaffolded site as well, which will also mean significantly smaller dependencies. That should hopefully lead to smaller binaries and quicker server setups. This is likely the last release in the 0.7 series. I'm in the middle of converting all of the packages over to 0.8 now. The two main features of that release will be WAI 0.4 and switching from String to Text throughout the codebase. Michael [1] http://hackage.haskell.org/package/yesod-0.7.3

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Yesod devel server and cabal-dev
by "Timo B. Hübel" 31 Mar '11

31 Mar '11

Hi, is it possible (if yes, how?) to use the Yesod devel server with a sandboxed environment from cabal-dev? My main problem is, that the devel server is not able to load (i.e. see) custom packages that I've added via "cabal-dev add-source" to the sandbox. I think it all boils down to specify a custom package path to the Hint interpreter. Any clues? Thanks, Timo

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Yesod. script incuding
by Anton Cheshkov 31 Mar '11

31 Mar '11

Hello Michael. Please show me the best way how to include <script src="http://example.com" charset="windows-1251"> The "addScriptRemote" functions have only single argument. Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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Yesod Examples
by Zachary Kessin 30 Mar '11

30 Mar '11

Ok, I'm trying to setup a handler to take data from a HTTP post, and store it into a database, This is what I came up with, but its not right. Can someone tell me what I am doing wrong. postPostMessageR :: Handler RepJson postPostMessageR = do liftIO $ putStrLn "POST" CharecterPost clients _ <- getYesod (text, charecter) <- do text <- lookupPostParam "text" charecter <- lookupPostParam "charecter" case (text, charecter) of (Just text', Just charecter') -> return (text', charecter') _ -> invalidArgs ["text not provided."] jsonToRepJson $ jsonMap (("text", text'),( "charecter", charecter')) --Zach

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Yesod renaming
by Greg Weber 29 Mar '11

29 Mar '11

Michael has floated the possibility of re-naming Yesod. Pro: * Something that everyone can pronounce * Something easier to remember * Something that invokes a meaningful mental impression (instead of a "what does that mean?"). Con: * Yesod is *very* distinctive, we'd most likely end up with a less unique name * People know Yesod already One other con we had was the re-naming effort, but I think we could mitigate that by continuing to use the Yesod name in the code to a large extent for a while. Would a phonetic spelling on the homepage help? yee-sode: high performance, type-safe web development Feedback on the issue is welcome. We are probably more concerned about thinking back to the initial impression someone gets of the framework when evaluating it or beginning to use it. It would be great to hear opinion from the international crowd.

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problem with working from a Yesod example, ajax.hs <reposted from Haskell-Cafe and Haskell-Beginnners>
by Michael Litchard 29 Mar '11

29 Mar '11

Something went wrong with my first post, and I suspect it may end up not getting through many spam filters. I decided to make another attempt, and it occurred to me this was the more appropriate mailing list anyway. I'm working off of a example file from Yesod, ajax.lhs I've made an important change in types, and this has resulted in having to make the old code conform to the change. I will point out the specifics, then present my question. In the event I failed to include important information, I will paste in my code as well as the prototype. [Original] > getHomeR :: Handler () > getHomeR = do > Ajax pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first [Changed] > getHomeR :: Handler () > getHomeR = do > Tframe pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first Error Message test.lhs:62:4: Constructor `Tframe' should have 2 arguments, but has been given 1 In the pattern: Tframe pages In a stmt of a 'do' expression: Tframe pages <- getYesod **** This is not what I wrote ***** In the expression: do { Tframe pages <- getYesod; content <- widgetToPageContent widget; hamletToRepHtml (hamlet-0.7.1:Text.Hamlet.Quasi.toHamletValue (do { (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "<!DOCTYPE html><html><head><title>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (Main.pageTitle content); .... })) } As far as I can tell, I only made a cosmetic change. I don't know what's going on here. [Original] > data Page = Page > { pageName :: String > , pageSlug :: String > , pageContent :: String ******** I'm going to change this ********** > } [Changed] > data Page = Page > { pageTitle :: String > , pageSlug :: String -- ^ used in the URL > , pageContent :: IO String ******** This is the change ******* > } Here's where I run into trouble [Original] > json page = jsonMap > [ ("name", jsonScalar $ pageName page) > , ("content", jsonScalar $ pageContent page) ******** I'm going to change this ******** > ] [My changes] > json page = jsonMap > [ ("name", jsonScalar $ Main.pageTitle page) > , ("content", jsonScalar $ liftIO $ pageContent page) ******* This is the change *********** > ] Here's the compiler error test.lhs:107:35: Couldn't match expected type `Char' against inferred type `[Char]' Expected type: String Inferred type: [String] In the second argument of `($)', namely `liftIO $ pageContent page' In the expression: jsonScalar $ liftIO $ pageContent page Failed, modules loaded: none. I'd appreciate a discussion about why this is wrong, and perhaps clues as to what is right. Last problem, stemming from the change in type to IO String. I don't have a clue as to what change I should make. test.lhs:100:25: No instance for (Text.Blaze.ToHtml (IO String)) arising from a use of `Text.Blaze.toHtml' at test.lhs:(100,25)-(103,3) Possible fix: add an instance declaration for (Text.Blaze.ToHtml (IO String)) In the second argument of `(.)', namely `Text.Blaze.toHtml' In a stmt of a 'do' expression: (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (pageContent page) In the first argument of `hamlet-0.7.1:Text.Hamlet.Quasi.toHamletValue', nam ely `do { (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "<h1>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (Main.pageTitle page); (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . preEscapedString) "</h1><article>"; (hamlet-0.7.1:Text.Hamlet.Quasi.htmlToHamletMonad . Text.Blaze.toHtml) (pageContent page); .... }' And finally, both files can be found below, if it is necessary to look at them. [Original] <p>We're going to write a very simple AJAX application. It will be a simple site with a few pages and a navbar; when you have Javascript, clicking on the links will load the pages via AJAX. Otherwise, it will use static HTML.</p> <p>We're going to use jQuery for the Javascript, though anything would work just fine. Also, the AJAX responses will be served as JSON. Let's get started.</p> > {-# LANGUAGE ScopedTypeVariables, TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses #-} > import Yesod > import Yesod.Helpers.Static > import Data.Monoid (mempty) Like the blog example, we'll define some data first. > data Page = Page > { pageName :: String > , pageSlug :: String > , pageContent :: String > } > loadPages :: IO [Page] > loadPages = return > [ Page "Page 1" "page-1" "My first page" > , Page "Page 2" "page-2" "My second page" > , Page "Page 3" "page-3" "My third page" > ] loadPages :: IO [Page] loadPages = do > > data Ajax = Ajax > { ajaxPages :: [Page] > , ajaxStatic :: Static > } > type Handler = GHandler Ajax Ajax Next we'll generate a function for each file in our static folder. This way, we get a compiler warning when trying to using a file which does not exist. > staticFiles "static/yesod/ajax" Now the routes; we'll have a homepage, a pattern for the pages, and use a static subsite for the Javascript and CSS files. > mkYesod "Ajax" [$parseRoutes| > / HomeR GET > /page/#String PageR GET > /static StaticR Static ajaxStatic > |] <p>That third line there is the syntax for a subsite: Static is the datatype for the subsite argument; siteStatic returns the site itself (parse, render and dispatch functions); and ajaxStatic gets the subsite argument from the master argument.</p> <p>Now, we'll define the Yesod instance. We'll still use a dummy approot value, but we're also going to define a default layout.</p> > instance Yesod Ajax where > approot _ = "" > defaultLayout widget = do > Ajax pages _ <- getYesod > content <- widgetToPageContent widget > hamletToRepHtml [$hamlet| > \<!DOCTYPE html> > > <html> > <head> > <title>#{pageTitle content} > <link rel="stylesheet" href="@{StaticR style_css}"> > <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"> > <script src="@{StaticR script_js}"> > \^{pageHead content} > <body> > <ul id="navbar"> > $forall page <- pages > <li> > <a href="@{PageR (pageSlug page)}">#{pageName page} > <div id="content"> > \^{pageBody content} > |] <p>The Hamlet template refers to style_css and style_js; these were generated by the call to staticFiles above. There's nothing Yesod-specific about the <a href="/static/yesod/ajax/style.css">style.css</a> and <a href="/static/yesod/ajax/script.js">script.js</a> files, so I won't describe them here.</p> <p>Now we need our handler functions. We'll have the homepage simply redirect to the first page, so:</p> > getHomeR :: Handler () > getHomeR = do > Ajax pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first And now the cool part: a handler that returns either HTML or JSON data, depending on the request headers. > getPageR :: String -> Handler RepHtmlJson > getPageR slug = do > Ajax pages _ <- getYesod > case filter (\e -> pageSlug e == slug) pages of > [] -> notFound > page:_ -> defaultLayoutJson (do > setTitle $ string $ pageName page > addHamlet $ html page > ) (json page) > where > html page = [$hamlet| > <h1>#{pageName page} > <article>#{pageContent page} > |] > json page = jsonMap > [ ("name", jsonScalar $ pageName page) > , ("content", jsonScalar $ pageContent page) > ] <p>We first try and find the appropriate Page, returning a 404 if it's not there. We then use the applyLayoutJson function, which is really the heart of this example. It allows you an easy way to create responses that will be either HTML or JSON, and which use the default layout in the HTML responses. It takes four arguments: 1) the title of the HTML page, 2) some value, 3) a function from that value to a Hamlet value, and 4) a function from that value to a Json value.</p> <p>Under the scenes, the Json monad is really just using the Hamlet monad, so it gets all of the benefits thereof, namely interleaved IO and enumerator output. It is pretty straight-forward to generate JSON output by using the three functions jsonMap, jsonList and jsonMap. One thing to note: the input to jsonScalar must be HtmlContent; this helps avoid cross-site scripting attacks, by ensuring that any HTML entities will be escaped.</p> <p>And now our typical main function. We need two parameters to build our Ajax value: the pages, and the static loader. We'll load up from a local directory.</p> > main :: IO () > main = do > > pages <- loadPages > let s = static "static/yesod/ajax" > warpDebug 3000 $ Ajax pages s [My changes] > {-# LANGUAGE TypeFamilies, QuasiQuotes, TemplateHaskell, MultiParamTypeClasses > #-} > import Yesod > import Yesod.Helpers.Static > import System.Environment > import System.IO > import System.Directory > import System.FilePath.Posix > import Control.Applicative > import Data.List.Split > data Page = Page > { pageTitle :: String > , pageSlug :: String -- ^ used in the URL > , pageContent :: IO String > } > loadPage :: IO [Page] > loadPage = do > let directoryPath = "/home/mlitchard/playground/webTests/files" > let processedPath = map (directoryPath </>) . filter (`notElem` [".",".."]) > pageFileNames <- processedPath <$> getDirectoryContents directoryPath > let pageFiles = map readFile pageFileNames > return $ zipWith popEntries pageFileNames pageFiles -- > return $ zipWith popEntries > popEntries :: FilePath -> IO String -> Page > popEntries pageFileName pageFile = > let pageT = last $ splitOn "/" pageFileName > pageS = "Job" ++ pageT > in Page { Main.pageTitle=pageT, > pageSlug=pageS, > pageContent=pageFile } > data Tframe = Tframe > { tframePages :: [Page] > , tframeStatic :: Static > } > type Handler = GHandler Tframe Tframe > staticFiles "static/yesod/ajax" Routes > mkYesod "Tframe" [$parseRoutes| > / HomeR GET > /page/#String PageR GET > /static StaticR Static tframeStatic > |] defining the Yesod instance > instance Yesod Tframe where > approot _ = "" > defaultLayout widget = do > Tframe pages <- getYesod > content <- widgetToPageContent widget > hamletToRepHtml [$hamlet| > \<!DOCTYPE html> > > <html> > <head> > <title>#{Main.pageTitle content} > <link rel="stylesheet" href="@{StaticR style_css}"> > <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"> > <script src="@{StaticR script_js}"> > \^{pageHead content} > <body> > <ul id="navbar"> > $forall page <- pages > <li> > <a href="@{PageR (pageSlug page)}">#{Main.pageTitle page} > <div id="content"> > \^{pageBody content} > |] > getHomeR :: Handler () > getHomeR = do > Tframe pages _ <- getYesod > let first = head pages > redirect RedirectTemporary $ PageR $ pageSlug first > getPageR :: String -> Handler RepHtmlJson > getPageR slug = do > Tframe pages _ <- getYesod > case filter (\e -> pageSlug e == slug) pages of > [] -> notFound > page:_ -> defaultLayoutJson (do > setTitle $ string $ Main.pageTitle page > addHamlet $ html page > ) (json page) > where > html page = [$hamlet| > <h1>#{Main.pageTitle page} > <article>#{pageContent page} > |] > json page = jsonMap > [ ("name", jsonScalar $ Main.pageTitle page) > , ("content", jsonScalar $ liftIO $ pageContent page) > ] > main :: IO () > main = do > > pages <- loadPage > let s = static "static/yesod/ajax" > warpDebug 3000 $ Tframe pages s If you've read to the bottom, thanks for your patience. I appreciate any illumination you can send my way. Michael

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Performance of Yesod 0.7 fourteen times slower than Rails 2.3?
by Sven Koschnicke (GFXpro) 28 Mar '11

28 Mar '11

Hello, I'm coming from a Rails background and was very impressed by the features of the Yesod Web Framework. Working on an trading app in Rails I wanted to port some features of this app to a Yesod app just to learn the framework and because we have some performance issues with Rails. The first thing I noticed was that the Yesod app was significantly slower than the Rails app at trivial tasks. I am very astonished about that. I thought Rails should be slower because of its interpreted nature. I made some benchmarking and measured that a simple Rails app is fourteen times faster than a Yesod app that did the same thing (loading some records from the database and displaying them). Did I made a mistake or is my understanding, that the compiled app should be faster, just wrong? I documented the results on github: https://github.com/SKoschnicke/performance-test Greetings Sven Koschnicke

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Haskell web application hosting
by Michael Snoyman 27 Mar '11

27 Mar '11

Hi all, JP Moresmau recently sent me an email asking for recommendations on hosting a Yesod app. I think a number of you have heard me mention the idea of setting up a WAI web hosting system (code named Lambda Engine). I think it's time to start hitting this idea hard, and I'd like community involvement as much as possible. I think we have two extremes we can approach this from: at the one end, we can provide a complete hosting solution, similar to Heroku[1]. People would simply "cabal sdist" their project, type "lambda-engine upload mytarball.tar.gz" and their site would be live. Lambda Engine would automatically handle database server configuration, DNS setup, and so on. At the other extreme, we could simply provide a set of shell scripts for setting up a vanilla Ubuntu (or Debian, or Cent, or FreeBSD...) install to support compiling a WAI application, provide an nginx setup, etc. The user would be responsible- and have the freedom to- set up his/her own server however he/she wants. There are lots of in-between points on that spectrum. For example, I was thinking of perhaps providing a central compilation server that everyone could use. In my experience, Haskell applications take very few resources to run, but actually building the things take a while. Compiling on a local system and then uploading is painful because (1) you have to deal with architecture issues and (2) you might have a slow upload speed. Anyway, I'm very interested to hear what other people think about all this. I'll enumerate a bunch of random thoughts on this topic: * Should this be a for-profit venture, bankrolled by a few members, or a community, non-profit approach? (I'm favoring the latter.) * If we decide to provide some serious hosting power, we might be able to make a deal with a hosting provider, stating that we're representing the "entire Haskell web community". * I don't really think this needs to be WAI specific: assuming we just use reverse HTTP proxies, this will work for any app that uses standalone hosting. We could also support FastCGI if we wanted. * Remember that Amazon is now providing a free tier, which provides a micro EC2 instance (available as either 32 or 64 bit). I think the micro instance should be sufficient for running a few web apps, nginx and PostgreSQL. * Since starting up and shutting down instances is so easy with Amazon, we could provide both a "web host" image and a "Haskell compiler" image. The web host could automatically start up a compiler instance as needed. * Are we going to provide email sending support, with all of the complications of dealing with spam lists, or simply offload to external services (like Amazon SES[2])? * Does anyone have a good recommendation on who to use as a host? Michael [1] http://heroku.com/ [2] http://aws.amazon.com/ses/

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