April 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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Ambiguous type variable `mo0' in the constraint + Understanding how Widgets work
by Mathew de Detrich 01 May '11

01 May '11

I am having issues figuring out how exactly widgets work within Yesod, having a look at the example here http://www.yesodweb.com/book/example-widgets <http://www.yesodweb.com/book/example-widgets>There is an example getHomeR = defaultLayout $ do setTitle "Polymorphic Hamlet" addHtml [$hamlet|I was added with addHtml|] addHamlet [$hamlet|I was added with addHamlet|] addWidget [$hamlet|I was added with addWidget|] Now assuming you have a Homer router set up, if you compile the example you get Ambiguous type variable `mo0' in the constraint: (or errors of that form). Asking on haskell irc, I found out this error is due to Haskell not knowing what type Hamlet returns, which is probably the reason for this comment "However, there is a more subtle point as well. While in theory a Hamlet template is polymorphic, this actually depends upon what values are embedded inside it (using ^{...} interpolation). For example, [$hamlet|^{someValue}|] will have the same type as someValue; if someValue is of type Hamlet, then so will the template." I assume that you are meant to have one ^{...} interpolation for every GET route request you are attempting to do, so checking the example code here here http://www.yesodweb.com/book/example-widgets, as I suspected the variable interpolation is used in the root handler and in the form handler (in the case for root handler it goes through a wrapper function). The issue is, when I attempt to use the ^{...} interpolation in my code (in this case I am literally just copying the wrapper function and passing it through with defaultLayout $ wrapper $ do as with the example) I am still getting the ambiguous type variable using this simple example getIndexR = defaultLayout $ wrapper $ do setTitle "Polymorphic Hamlet" addHtml [$hamlet|I was added with addHtml|] addHamlet [$hamlet|I was added with addHamlet|] addWidget [$hamlet|I was added with addWidget|] Am I missing something fundamental here, because I am at odds of what to do at this point (I am using yesod 7.0.3 if that matters). Also is there a non trivial example of how combinating widgets is done to form a combined web page (containing CSS, HTML and JS), i.e. whats mentioned here "The job of a widget is to hold onto these disparate components and apply proper logic for combining different widgets together. This consists of things like taking the first title set and ignoring others, applying nub to the list of external scripts and stylesheets, and simply concatenating head and body content." Thanks

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juliusFile in yesod 0.8 eating all memory
by JP Moresmau 30 Apr '11

30 Apr '11

Hi all, I've just upgraded to Yesod 0.8. I've changed all my Strings into Texts, and all my Data.JSON.Types into Data.Aeson.Types. I use these JSON objects in julius templates, by adding the orphan instance: instance (ToJSON a)=> ToJavascript a where toJavascript =toJavascript . toJSON (Removing that instance causes compilation error, and I had it when I was using json-types). addJulius works fine when it contains Javascript code. However on one page I use juliusFile to load an external template. This eats all my memory and never returns under Warp when I launch the compiled exe (I see "thread killed" messages in the console, though), and in GHCi crashes with "out of memory". The code hasn't changed and was working fine in yesod 0.7 before the upgrade. If I remove juliusFile the page displays instantly. Any idea? I'm a bit stumped. I suppose I'm going to remove each of my variables in the julius file to narrow it down, but if anybody has any insight... Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Yesod. Pesistent
by Anton Cheshkov 30 Apr '11

30 Apr '11

Hello. I have some confusing with PersistValue I have two variables UserProfileId {unUserProfileId = PersistText "1"} which obtained from* fromSinglePiece* come from HTML Form UserProfileId {unUserProfileId = PersistInt64 1}" is *Key UserProfile *came from Database Logically i expect that this values must be equal. But haskell says me not ) How to get equality ? Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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Fixing yesod devel
by Michael Snoyman 29 Apr '11

29 Apr '11

Hi all, I've been trying to figure out a better solution to the yesod devel issue (the new development server). I've just pushed a commit to Github which *does* work, albeit clumsily. The basic process now is to install the package into the global database (like before), and use an external process call to runghc to run the server. There's a *lot* of hacks in the code, but it seems to mostly work now. I'd appreciate it if people can give it a test and give me some feedback. I'm short on time now, but if anyone is interested in helping me out with this, please let me know and I'll give you the full gory history on the failed attempts (direct-plugins, plugins, hint, GHC API...). Michael

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problems using yesod scaffolding
by Michael Litchard 28 Apr '11

28 Apr '11

running yesod with the mini option caused some problems. I got complaints of not being able to find Settings.hs, so I made some changes to the import statements. Also, I changed the directory config to Config to accommodate my changes. Here's what the import sections look like now Aframe.hs module Aframe ( Aframe (..) , AframeRoute (..) , resourcesAframe , Handler , Widget , module Yesod.Core , module Config.Settings <---- made a change here , StaticRoute (..) , lift , liftIO ) where import Yesod.Core import Yesod.Helpers.Static import qualified Config.Settings as Settings <---- made a change here import System.Directory import qualified Data.ByteString.Lazy as L import Config.Settings (hamletFile, cassiusFile, juliusFile, widgetFile) <----- made a change here import Config.StaticFiles <----- made a change here import Control.Monad (unless) Controller.hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE OverloadedStrings #-} {-# OPTIONS_GHC -fno-warn-orphans #-} module Controller ( withAframe , withDevelApp ) where import Aframe import qualified Config.Settings as Settings <---- made a change here import Yesod.Helpers.Static import Data.ByteString (ByteString) import Network.Wai (Application) import Data.Dynamic (Dynamic, toDyn) that said, I get out of scope errors when I try to run the scaffolding generated code mlitchard@apotheosis:~/repository/Aframe$ wai-handler-devel 3000 Aframe withDevelApp Attempting to interpret your app... Compile failed: Not in scope: `withDevelApp' also get the same problem when trying withAframe I can't see the reason for the out of scope problem. I think it has to do with the changes I made. Anything suspicious pop out for anyone?

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wai-handler-devel and yesod 0.8
by Matias Eyzaguirre 28 Apr '11

28 Apr '11

I'm trying to use wai-handler-devel with an application created using the yesod-0.8.0 scaffolding tool, but I'm running into some trouble. After some missing modules I symlinked some of the modiles in the 'config' folder into the root directory, but then I get a somewhat enigmatic type error that seems somewhat nonsensical: <log> Holly:Voluntrack dented42$ wai-handler-devel 3000 Controller withVTrack Attempting to interpret your app... Compile failed: Couldn't match expected type `Network.Wai.Request' with actual type `Network.Wai.Request' </log> what exactly does that mean? or rather, what should I do to prevent it? Perhaps it's trying to match the same type in two different versions of a package? Or might it be something else? Thanks, Matias Eyzaguirre

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Problem installing yesod-form 0.1.0
by Sven Koschnicke 28 Apr '11

28 Apr '11

Hello, today I tried to update to yesod 0.8, but cabal install fails at building yesod-form 0.1.0: [3 of 8] Compiling Yesod.Form.Jquery ( Yesod/Form/Jquery.hs, dist/build/Yesod/Form/Jquery.o ) [4 of 8] Compiling Yesod.Form.Nic ( Yesod/Form/Nic.hs, dist/build/Yesod/Form/Nic.o ) [5 of 8] Compiling Yesod.Form.Fields ( Yesod/Form/Fields.hs, dist/build/Yesod/Form/Fields.o ) [6 of 8] Compiling Yesod.Form.Class ( Yesod/Form/Class.hs, dist/build/Yesod/Form/Class.o ) [7 of 8] Compiling Yesod.Form ( Yesod/Form.hs, dist/build/Yesod/Form.o ) [8 of 8] Compiling Yesod.Helpers.Crud ( Yesod/Helpers/Crud.hs, dist/build/Yesod/Helpers/Crud.o ) Yesod/Helpers/Crud.hs:63:25: Not in scope: `toSinglePiece' Yesod/Helpers/Crud.hs:97:39: Not in scope: `fromSinglePiece' Yesod/Helpers/Crud.hs:109:39: Not in scope: `fromSinglePiece' Yesod/Helpers/Crud.hs:120:39: Not in scope: `fromSinglePiece' Yesod/Helpers/Crud.hs:144:39: Not in scope: `fromSinglePiece' Yesod/Helpers/Crud.hs:166:42: Not in scope: `toSinglePiece' Yesod/Helpers/Crud.hs:172:25: Not in scope: `toSinglePiece' ... cabal: Error: some packages failed to install: yesod-0.8.0 depends on yesod-form-0.1.0 which failed to install. yesod-auth-0.4.0 depends on yesod-form-0.1.0 which failed to install. yesod-form-0.1.0 failed during the building phase. The exception was: ExitFailure 1 I already tried to remove .cabal and .ghc, but a fresh install fails with the same error. I have ghc 7.0.2 running on macos 10.7 > cabal --version cabal-install version 0.10.2 using version 1.10.1.0 of the Cabal library Thanks Sven Koschnicke

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Yesod. Cookie. Lookup
by Anton Cheshkov 27 Apr '11

27 Apr '11

Michael. Show me please how do to lookup cookies in yesod. Thanks. -- Best regards, Cheshkov Anton Phone: +7 909 005 18 82 Skype: cheshkov_anton

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persistent and mysql
by Max Cantor 27 Apr '11

27 Apr '11

I've heard that there is a mysql backend in development for persistent. what is its current status? before you start telling me how postgres is better, let me say that I know it is. but, the AWS RDS implementation of MySQL is very compelling and kind of makes up for the differences.. Max

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