July 2011 - web-devel

Including a static css file
by Anakreon Mentis 18 Jul '11

18 Jul '11

I am experimenting with yesod and am new to it. I changed the default-layout.hamlet file of a project created by yesod init. The modification consists of the following line <link rel="stylesheet" type="text/css" href="@{StaticR css/base.css}"> I get an error message " (line 4, column 48): unexpected 'h' expecting end of input, "\n", "\r\n" or ">" The file static/css/base.css does exist.

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[Yesod] psuedo-announcement: yesod-goodies
by Patrick Brisbin 17 Jul '11

17 Jul '11

Hey all, Just wanted to post a quick note here about a package I've started with various little utilities that I find generally useful enough to be used across different yesod sites. The best explanation is probably by way of example, so here's what it provides so far: Y.G.Gravatar : fetch a gravatar image for an email address Y.G.Links : concise internal/external link-widgets Y.G.Markdown : a slightly altered version of yesod-markdown Y.G.Paginate : paginate a large list of items Y.G.Search : a type class engine behind search pages Y.G.Shorten : a type class to shorten a variety of... Y.G.Time : prints UTCTime as "one hour ago", etc That last one was taken from haskellers.com (hope you don't mind Michael). The package has been on hackage[1] for a bit and the source is on github[2]. Feel free to contribute if you've got your own goodies. Thanks, Pat 1: http://hackage.haskell.org/package/yesod-goodies 2: https://github.com/pbrisbin/yesod-goodies -- patrick brisbin

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Payment Processing
by John Lenz 16 Jul '11

16 Jul '11

Hi, I am in the middle of writing a small website in haskell, and am at the point of investigating a payment processing solution. Does anyone have any experience? As far as I can see, there aren't any libraries on hackage. I am strongly considering Google Checkout, since then I don't have to deal with credit cards directly and can just let google do it. So I am considering starting a hackage library for google checkout, anybody interested in helping out? I think xml-enumerator with http-enumerator should work well. I have been thinking about the API such a package should have, and I am currently leaning towards a combinator approach like blaze. The google xml schema for items [1] has so many optional parts that if we try and define a record, it will have a ton of Maybe's in it. Generating the xml using a combinator approach seems better. But this would only be my second library on hackage, so any suggestions for how you think the API should look are appreciated :) Thanks, John [1] - http://code.google.com/apis/checkout/developer/Google_Checkout_XML_API.html…

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[Newbie] Basic concepts around passing a JSON value to a JQuery function for processing.
by Michael Litchard 15 Jul '11

15 Jul '11

Not only am I new to Haskell and Yesod, but now I find I need JQuery and have some conceptual questions. The stiuation I have is I am trying to build a status page that will either give information about a live server, or an alert saying that it's down. I want to have a BOOL to pass. How do I go about passing values from my Yesod program to an JQuery function?

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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…

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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

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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

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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

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JS caching
by Mister Asafe Ribeiro 13 Jul '11

13 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)?

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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

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