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[Yesod] blog tutorials
by いとうかつとし 11 Nov '10

11 Nov '10

Hi I'd like to learn how to use Jqeury, Nic and Crud on scaffolded by 0.6.*. Are there simple sample like as blog2 screencast(but this tutorial is too old to work on 0.6.*)? ---- Katsutoshi Itoh<cutsea110(a)gmail.com>

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Yesod's Route as a data family
by Matt Brown 10 Nov '10

10 Nov '10

Hi all, I'm trying to create a yesod subsite with "private" urls. The subsite exports widgets which reference the urls, but the urls are not intended to be referenced from the master site handlers directly. In order for this to work, the sub site needs to know how to translate it's urls into master urls. I didn't like passing the subsite route as a parameter to every widget function, so I tried a class: class YesodSubRoute sub master where subRoute :: Route sub -> Route master After confronting the dreaded "type families are not injective" error (i.e. "sub" cannot be inferred from "Route sub", etc), I rewrote it as: class YesodSubRoute sub master where subRoute :: sub -> master -> Route sub -> Route master This works, but seems a bit cludgy to me. Looking closer, I realized that mkYesodGeneral never reuses types for Route instances, which means Route actually is injective (as long as instances are only being defined by mkYesodGeneral), the typechecker just doesn't know it. As an experiment, I changed Route to a data family. It went rather smoothly, and I was able to use my original definition of YesodSubRoute (instances of which could in theory be generated by mkYesodGeneral). The only trouble I've had is exporting Route instance constructors imported from another package (specifically yesod-auth in my case), which means every module referencing auth routes has to import Yesod.Helpers.Auth). Relevant commits are below. Does this seem like a sensible approach? Are there better alternatives? thanks, -matt https://github.com/softmechanics/yesod/commit/335722b6b234841492a6fba2eb46b… https://github.com/softmechanics/yesod-auth/commit/baf9b44978aad4dba9b86cfa…

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Re: anybody have toy examples of using digestive functors formlets lib?
by Jeremy Shaw 06 Nov '10

06 Nov '10

Hello, I have a attached a little demo that shows how I like to use digestive functors. The primary issue right now is that it does not work correctly if you try to put more than one formlet on a page. (due to an issue in my code). It is fixable -- I just have not had the time and need quite yet. Though, if you can skip the use of digestiveFunctorPart and use digestive-functors-hsp the 'normal' way. To run the demo you will need: - lastest happstack from darcs - lastest digestive-functors from git, https://github.com/jaspervdj/digestive-functors - lastest digestive-functors-hsp from darcs, http://src.seereason.com/digestive-functors-hsp Furthermore, you will need to edit the digestive-functors.cabal file and change, monads-fd to mtl < 2. That will change later this week when I switch happstack from mtl to monads-fd. (Or *you* could patch happstack to use monads-fd and send me a patch). If you do not make that change, then you will get an overlapping instance error regarding MonadPlus IO. If you do not want to update to the lastest happstack, you will just have to look at the attached code and reverse engineer what you want to do. Though, I recommend upgrading to happstack from darcs. It will break your code, but I think I made all the code breaking changes for the next release, so you can get it over with now :p Or, if you are using it for a new project, you can start with the good stuff and not have to upgrade it later. The happstack crash course documents the darcs version of happstack. I will eventually add a section to the happstack crash course on this technology. But until then, I hope this gets you started. Note that the rendering is ugly because there is no CSS applied. You can use 'setAttr' in the digestive-functors-hsp library to set some class attributes and then apply some CSS to pretty things up. Also, jaspervdj mentioned something in the README about better ways to theme a form than what formlets offered. I have no idea what that refers too. But maybe it is better than using setAttrs. Note that both digestive-functors and digestive-functors-hsp are very new. If you think something about them is wacky, please let us know. Don't assume that when meant for things to be stupid. - jeremy On Fri, Nov 5, 2010 at 6:32 PM, Thomas Hartman <thomashartman1(a)googlemail.com> wrote: > anybody have toy examples of using digestive functor library? > Especially with hsp, which is my usual templating system these days? > A couple of people have recommended this library to me but I don't see any > easy way to get started using it. > Toy example would be great. > Thanks a bunch! > thomas.

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Yesod gotcha (kind of, not sure, it got me good though)
by Nubis 03 Nov '10

03 Nov '10

Hi guys, I'm fully getting into haskell thanks to the yesod framework. I've been pulling my hair with a bug as silly as they come, and for so long that I cannot tell it without feeling embarrassed. (I'm working on the haskellers.com website code, just to give you some extra context) I was getting a 500 in one of my controllers, and I first though there was some non existing id being referenced from a model, I set up the haskell interactive debugger and launched my yesod project from ghci, single stepped and everything looked just fine. The actual error displayed was:"Internal Server Error" "A LineSingle must have nested content" The issue was finally that a cassius file had some trailing garbage (that went unnoticed by me, probably added accidentally when passing out over my keyboard). My main issue with this is that I think of cassius files as just css, I wouldn't expect to get an error in my page just for a broken css file. I would expect seeing broken styles, or even better, the program not compiling at all. I searched for the LineSingle error message and seems to be related to hamlet, I interpreted that as a pointer but was in the wrong direction. I know this won't happen to me again, but just wanted to throw it out here to see if you consider it a gotcha. cheers :) ----nubis :)

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Single step debugging a yesod application
by Nubis 03 Nov '10

03 Nov '10

Hi guys, As I said in another thread, I've been debugging a yesod application single stepping through one of the handlers. I'm using ghci built in debugger and it's pretty good, but I always fail to set the breakpoint in the right scope where I can evaluate the stuff I'm interested in learning more about. For instance, in the following code I would like to set the debugger on the line before "mv <- maybeAuth", in order to :force the values of (uid, u). But even when I set it at the beginnig of the 'mv' line, the scope ends up being the entire do block. Which makes sense, but doesn't helpe me solve my problem :) getUserR :: String -> Handler RepHtmlJson getUserR input = do (uid, u) <- case readIntegral input of Just uid -> debugRunDB $ do u <- get404 uid mun <- getBy $ UniqueUsernameUser uid case mun of Nothing -> return (uid, u) Just (_, Username _ un) -> lift $ redirect RedirectPermanent $ UserR un Nothing -> debugRunDB $ do mun <- getBy $ UniqueUsername input case mun of Nothing -> lift notFound Just (_, Username uid _) -> do u <- get404 uid return (uid, u) mv <- maybeAuth Maybe the problem is that I'm thinking in a too procedural fashion about do blocks, or that evaluating those results is kind of paranoid. I'm too spoiled by REPL's, I would even like to be able to use a REPL that runs inside runDB for querying models and doing stuff with them interactively. How do you debug your yesod apps? am I drifting too far away from the haskell way? thanks in advance for your comments :) cheers ----nubis

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[Yesod] How can I layout 2 random banana forms into 1 page?
by いとうかつとし 02 Nov '10

02 Nov '10

Hi, I'm beginning to learn yesod programming. I just write random banana tutrial.(ref. http://docs.yesodweb.com/book/forms/) And the program work good, after installed safe package. Now, I'd like to layout 2 paramsFormlet into 1 page(getHomeR) and expect to work independently. But my program(with this mail) don't work independently. I know these id and name attributes of input tags are same between 2 paramsFormlet's. But I don't know why and how to modify. Could you tell me a solution? ---- Katsutoshi Itoh <cutsea110(a)gmail.com>

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New Persistent Meta-Backend for Horizontal Partitioning - Difficulty?
by Max Cantor 02 Nov '10

02 Nov '10

I like Persistent for its simplicity and ease of use compared to the other, more full-featured DB libraries on Hackage. There is one feature which I am interested in but am curious what the community thinks of it. My idea is to support horizontal partitioning via a new Persistent backend which is more of a meta backend that redirects queries to any number of child backends. I think it shouldn't be too difficult. Persistent's simplicity and not supporting joins makes this much easier. The meta-backend simply needs have references to the child back ends and some sort of "chooser" function that says which data goes where. Queries which need to be executed across the children could run in parallel (with some restrictions on things like sorting). Anyway, just a thought. I'm curious if this community thinks this would be useful given that tools like pgpool exist. I've heard some bad things about pgpool which is why I was thinking about this. Furthermore, glancing at the code for the current backends, it doesn't *seem* like a ton of work, but I am far from convinced. So, what does everything thing?

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Question for y'all: simplifying cassius
by Michael Snoyman 28 Oct '10

28 Oct '10

Hey all, Cassius (the CSS template language that goes along with Hamlet[1]) has some features which I've never advertised, and frankly never use: * mixins * nesting My question is: will anyone miss them if they're gone? Right now, neither one of these features is implemented in a good way: mixins requires a special datatype, a separate quasi-quoter, and don't always work as expected. Nesting doesn't do what you expect often, eg: p, div .some-class color: red Generates: p, div .some-class { color: red } As a result of having these two features, cassius is overall worse: * You *must* put a space between the colon and the attribute value. This has to do with determining if we're nesting and pseudo-classes. * The error messages are rotten. I have no doubt that all of these problems could be fixed, given some time. However, I personally don't actually find that I need these features, and if no one else is using them right now, I'd rather release a new version of Hamlet without this extra weight and perhaps come back to these features in the future. By the way, if anyone is interested in tackling this stuff, I imagine the proper way to get it working would involve using an intermediate datatype that keeps line/column information, and then rendering that intermediate datatype using blaze. It won't be quite as fast as the current approach, but I highly doubt Cassius is going to be a bottleneck in anyone's applications. Michael [1] http://hackage.haskell.org/package/hamlet

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Yesod change: mutable session
by Michael Snoyman 26 Oct '10

26 Oct '10

Hey all, One of the things which has been a stumbling block of Yesod users has been the semantics of setSession. In particular, it seems strange that this does not work: myHandler = do setSession "foo" "bar" Just "bar" <- getSession "foo" Up until now, I have kept the "input" session that the user submitted in his/her request separate from the "output" session which will be sent in the response. I've just pushed a change to the repo which modifies things so the above code works. I don't *think* this will break anyone's code, unless you were relying on the old behavior in a strange way I can't think of. If this causes anyone problems, please let me know soon; Yesod 0.6 should be released either today or tomorrow. Michael

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Yesod change for 0.6: CSRF protection
by Michael Snoyman 25 Oct '10

25 Oct '10

Hey all, This should probably go in a blog post (and it probably will yet), but I wanted to get some quick feedback on an upcoming change for 0.6. Greg Weber pointed out that Yesod currently has no Cross Site Request Forgery (CSRF) protection, so I've made a patch that addresses this. You can see the code on the ver0.6 branch on github[1], but here's a bird's-eye view of the solution: * Each session will be assigned a random, 10-character nonce. * runFormPost will check for a _nonce hidden field and ensure that it matches the nonce for the session. If not, it causes a FormFailure. * runFormPost now returns a 4-tuple, containing the result, the form xml, the encoding type and an Html value for the nonce hidden field. You may be wondering why I don't just stick the hidden field directly in the xml. The reason is that we don't know the type of the xml value: it may be a FieldInfo, a Widget, a Hamlet, Html, anything. Also, even if we knew the datatype, we don't know *where* to append the nonce. For example, if the xml value is a collection of <tr> tags, it would generate invalid markup to simply append an <input> tag there. I've also added a runFormPostNoNonce which has the same behavior as the old runFormPost. I've specifically renamed the unsafe version to something wordier so that current code will be prompted to reconsider whether or not to check the nonce. I know this may cause significant code breakage, so I'd appreciate user feedback on this one. Michael [1] http://github.com/snoyberg/yesod/tree/ver0.6

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