September 2010 - web-devel

Interpolation character in Julius
by Michael Snoyman 20 Dec '10

20 Dec '10

Hamlet, Cassius and (currently) Julius all use a consistent set of characters for interpolation. The dollar sign ($) is for plain scalars, the at sign (@) is for URLs and the caret (^) is for embedding other templates (mixins in the case of Cassius). I like this consistency. Unfortunately, in the case of Julius, the dollar sign is a suboptimal character to use since jQuery uses is so extensively. Currently, to write some simple jQuery Javascript such as: $("h1").hide() you have to use a double dollar sign to achieve escaping, namely: $$("h1").hide() So the questions to the list are: * Is it worth trading consistency for a better choice of interpolation character? * If so, what would be a more optimal interpolation character? I think percent sign (%) might be acceptable. Interpolation is not as important in Julius as it is in Hamlet, so I'm beginning to lean towards replacing the character. Michael

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Re: [web-devel] Getting the http request header in Yesod?
by Rehno Lindeque 27 Sep '10

27 Sep '10

On Sun, Sep 26, 2010 at 2:04 AM, Rehno Lindeque <errantkid(a)gmail.com> wrote: > Thank you, that sounds exactly like what I need. I didn't notice it before! > > Rehno > > On Sat, Sep 25, 2010 at 6:57 PM, Michael Snoyman <michael(a)snoyman.com> wrote: >> On Sat, Sep 25, 2010 at 10:32 AM, Rehno Lindeque <errantkid(a)gmail.com> wrote: >>> I'm looking to detect ajax requests sent to my yesod application using >>> the technique detailed in http://davidwalsh.name/detect-ajax >>> >>> Is it possible to gain access to the request header directly or would >>> yesod require modification to get at it? If someone could just point >>> me in the right direction, I would be grateful. I imagine it would be >>> a function returning GHandler? >> >> You can use waiRequest[1] to get access to the WAI request value, and >> requestHeaders[2] to get the request headers from it. It's very >> convenient to use the OverloadedStrings extensions when dealing with >> the CIByteString datatype[3]. >> >> Hope that helps, >> Michael >> >> [1] http://hackage.haskell.org/packages/archive/yesod/0.5.0.3/doc/html/Yesod-Re… >> [2] http://hackage.haskell.org/packages/archive/wai/0.2.0/doc/html/Network-Wai.… >> [3] http://hackage.haskell.org/packages/archive/wai/0.2.0/doc/html/Network-Wai.… >> > Thanks a lot, this was very helpful! One more question. Is it possible to manipulate the request header when doing a redirect? For example, at one I have (redirect RedirectTemporary $ AuthR LoginR), but "X-Requested-With" isn't being passed through...

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WAI and Apache?
by Kevin Jardine 25 Sep '10

25 Sep '10

I'm interested in implementing web apps in a reasonably standards supporting way and I came across WAI. Is this something that I can run with Apache and mod_fastcgi? Sorry if this is a naive question. Kevin

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Getting the http request header in Yesod?
by Rehno Lindeque 25 Sep '10

25 Sep '10

I'm looking to detect ajax requests sent to my yesod application using the technique detailed in http://davidwalsh.name/detect-ajax Is it possible to gain access to the request header directly or would yesod require modification to get at it? If someone could just point me in the right direction, I would be grateful. I imagine it would be a function returning GHandler? Thanks, Rehno

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On the state of Haskell web frameworks
by Christopher Done 22 Sep '10

22 Sep '10

For what it's worth, I thought I'd throw a simple web app into the mix, hpaste.org: * Address http://hpaste.org/ * Source http://github.com/chrisdone/amelie The notable thing about this application is it's easy to see all the requirements ("small libraries"): 1. CGI/FastCGI: I needed a way to talk to the web, I chose CGI/FastCGI. The CGI library is quite general and small. 2. highlighting-kate: I needed to do syntax highlighting. Notice how it's just a few lines in an isolated module: http://github.com/chrisdone/amelie/blob/master/src/Amelie/Highlight.hs 3. Takusen: I needed to talk to a PostgreSQL database to save/read pastes, just a few lines (for setup) in an isolated module: http://github.com/chrisdone/amelie/blob/master/src/Amelie/DB.hs 4. ConfigFile: I needed a way to store the service's settings in a configuration file. Again, just a few lines in an isolated module: http://github.com/chrisdone/amelie/blob/master/src/Amelie/Config.hs 5. blaze-html/xhtml: I needed a way to build HTML inside my program. 6. formlets: I needed a way to generate and validate forms (e.g. the paste form). 5 and 6 are used in the HTML module: http://github.com/chrisdone/amelie/blob/master/src/Amelie/HTML.hs All of these libraries are perfect, they do one thing and do it well. I just imported them and they did the work for me. You can see also how they are modules in themselves, not interdependent as part of some grand framework. It seems that with good libraries, the architecture of your web app just designs itself. Personally I've always thought the "MVC" approach isn't particularly novel and follows naturally from good design. I'm not saying mine is good design, but without putting much conscious thought towards it, I've ended up with a DB module (model), a Pages module (controller) and a HTML module (view). To make this into the MVC approach, I'd just rename them to Model.hs, Controller.hs and View.hs. The things that I had to implement myself are as follows: 7. URI routing: http://github.com/chrisdone/amelie/blob/master/src/Amelie/Routes.hs How to receive requests and map that into a page + parameters to that page (e.g. paste/pid/30196 -> pastePage [("pid","30196")]), how to *generate* a URL with parameters. And how to generate a *pretty* URL: http://github.com/chrisdone/amelie/blob/master/src/Amelie/Links.hs A URL that maps back to a normal URL (e.g. http://hpaste.org/30196/half_a_proof is actually rewritten by nginx to http://hpaste.org/paste/id/30196) I think there probably are quite a few URI routing libraries out there but I only gave it a cursory glance. 8. Simple template writing. http://github.com/chrisdone/amelie/blob/master/src/Amelie/Templates.hs In fact I found that tibbe already wrote something to do this: http://hackage.haskell.org/package/template but I didn't end up using it for some reason. Maybe because everything has to be Text and I couldn't be bothered littering my code with string conversions all over the place. Turned out I had to do that anyway. Converting between String and ByteString and lazy ByteString and now Text is a real pain but you have to do it because all these different libraries decided to use a particular type. (At least some let you implement a Stringable class.) I will probably eventually just replace the templating code with tibbe's or go the full hog and use HStringTemplate. It's all the same idea, just more or less engineered. I'm interested in your thoughts and ideas. If you have any hpaste-size web applications that you have available online to read that you can maybe summarise and evaluate in the same way I have above, maybe that can spark some interesting discussion. Cheers!

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Proposed changes to web-routes: query-string support
by Michael Snoyman 21 Sep '10

21 Sep '10

Hi Jeremy, I've CCed the web-devel list, as I think the discussion will be of interest to a number of readers there. When we were originally working on web-routes, you had mentioned the idea of including some form of support for query strings, and I said it was a bad idea. I'd like to backtrack on that statement: I *would* like to include support, and I'm including a patch that does just that. Let me explain the use case this is meant to serve, which will help explain my design decisions. Yesod includes a static file subsite. One trick a lot of sites are using these days is including a hash of the file contents in the query string of the URL and setting the expiration date of the file far in the future. This way, as long as the file contents stay the same, the browser should use the cached copy, and as soon as a new version is available, the HTML will reflect this by a change in the hash value. I wanted to provide this feature with Yesod, but realized there was no straight-forward way to do this. What I needed was to change the formatPathSegments function to have a type signature of: url -> ([String], [(String, String)]), where the second element in the tuple is the query-string parameters. This, however, presents a small problem: let's say that we want to add query string parameters *on top of* those provided by the formatPathSegments function; we could do manually addition textually, but we won't know whether to include is as "?foo=bar" or "&foo=bar"; the former should be used if formatPathSegments does not given any query string parameter, the latter if it does. I therefore modified the handleSite function to be: (url -> [(String, String)] -> String) -> url -> a. I also changed encodePathInfo to also encode the query string parameters, so its type is now: [String] -> [(String, String)] -> String. All the other changes were just to get the code to compile. I'm planning on this being a change throughout a few other libraries: web-routes-quasi will obviously change to reflect this, as will Yesod. One other perhaps unexpected change would be in Hamlet: the definition of Hamlet is now "type Hamlet = (url -> [(String, String)] -> String) -> Html ()". One nice side effect of this is query-string encoding code is now completely localized to web-routes, instead of copied throughout multiple packages. This at least implies to me that this is a good move. You'll notice that I have purposely *not* modified decodePathInfo and parsePathSegments; I still don't believe routing should be affected in any way by query string parameters. Look forward to hearing your thoughts on this, Michael

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A URL by another name...
by Michael Snoyman 20 Sep '10

20 Sep '10

Here's an opinion question for the web-devel list. In Yesod, I try to ensure that we keep a single canonical URL for each resource, and redirect non-canonical URL there. For example: /foo/bar ---> /foo/bar/ /foo//bar/ ---> /foo/bar/ /static/myfile.png/ ---> /static/myfile.png There are essentially two components to this cleanup: collapsing multiple slashes and dealing with the trailing slash. If you pay careful attention to the example above, you'll notice that there's a subtlety to this trailing slash rule: * If the last piece of the URL contains a period, it is assumed to be a filename + extension, and therefore no trailing slash is used. * Otherwise, a trailing slash is used. My question is whether people would prefer a different default rule. (I say default because you can easily override this setting using the splitPath and joinPath functions.) The other two rules I could think of are always requiring or always banning the trailing slash. I think the former will make filenames look strange, but I don't really have a strong feeling on the latter. So the question is, what do y'all think? Cheers, Michael

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Web development work
by Michael Snoyman 16 Sep '10

16 Sep '10

Hi all, Often times when trying to pitch Haskell to potential clients the concern is the lack of qualified developers willing to take on projects. As I'm sure many of you are familiar with, clients prefer not to be locked in to a single programmer: an errant bus can significantly reduce the value of their investment. So I'd like to get an idea of how many people out there would be interested in Haskell web development work. For the moment I'm just interested in doing this informally via email, though perhaps in the future it would be beneficial to the community to have this information centralized on a website. I think it would be useful to have some basic skills and experience information, including system administration abilities. I might also have one or two Yesod projects that I'll need to pass off in the future, though it's still unclear if this will happen. If you're interested in that, please let me know, I can give some more details privately. Michael

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Upgrading from Yesod 4.0 to 5.0
by Rehno Lindeque 14 Sep '10

14 Sep '10

Hi all, I'm upgrading UrbanListing to Yesod 5.0 from 4.0 after a long hiatus. So I'm feeling a bit rusty :) I was wondering about the new signature for StaticRoute: > StaticRoute [String] [(String, String)] What is the purpose of the second argument [(String),(String)]? I couldn't pick it up from the documentation. Regards, Rehno

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