April 2011 - web-devel

Is $with in Yesod 0.8 ?
by vagif.verdi＠gmail.com 19 Apr '11

19 Apr '11

Is $with included in Yesod 0.8 ? or will it be released later ? Regards, Vagif Verdi

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Minor delay of Yesod 0.8
by Michael Snoyman 19 Apr '11

19 Apr '11

Hi all, Just wanted to let you know: there's been a minor delay in the 0.8 release of Yesod, all for good reasons. Rick Richardson and Greg Weber have put in a lot of work on the MongoDB backend for Persistent, and now we'll be able to include it (as an alpha) with this release. Congrats to them, this is very cool. The second reason is that I decided to be naughty and completely disregard my feature freeze. As we've discussed recently, there are some issues with our hint-based wai-handler-devel approach. Without going into too many details (both to keep from boring you, and because I have very little time before Passover starts), I've made the following modifications to the yesod scaffolding tool: * Running "yesod" by itself gives you a list of commands. * Running "yesod init" gives the behavior previously held by "yesod", i.e. generate a scaffolded site. * Running "yesod build" is *almost* identical to "cabal build", but with one change: it performs a dependency analysis of external files included by Template Haskell (Hamlet templates, routes, entity definitions) and changes modification times as needed to force cabal to build modules. For example, if "Handler/Root.hs" references "hamlet/root.hamlet", and the latter has a later modification time than the former, the former's modification times will be changed to match that of the latter. * Running "yesod devel" runs devel server. Instead of using hint, the devel server now uses cabal for the compiling (passing in a special "devel" flag) and direct-plugins to load up the compiled code. In order to make this work, there are a few necessary modifications to an individual site: * The "Controller" module now needs to have a "withDevelApp" function, which must be of type "Dynamic". The internal type of this must be "(Application -> IO ()) -> IO ()". * The cabal file must provide a library section. The library should only be built when the devel flag is passed in, it should be compiled with "-O0" (to speed up compiling) and executables are disabled (also for speed). * direct-plugins can only load up installed packages, so "yesod devel" will actually install your package. * The scaffolded site has already been updated to work properly with "yesod devel", so you can base your modifications on that. The only bug I'm aware of right now is that if a file disappears at the wrong time then the call to get the modification time will fail. This may seem far fetched, but it happened to me when saving a file with vim. Shouldn't be too hard to fix, I just don't have time right now. The code's on Yackage. If anyone wants to give it a shot, feel free. Michael

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[Yesod]How to write non-UTF8 encoded web service.
by Katsutoshi Itoh 19 Apr '11

19 Apr '11

Hi I think trying to support a mobile phone. There are three mobile phone carrier, in Japan. To accommodate all carriers instead of UTF-8 CP932(known as Shift_JIS) in the code word you need to interact with the Web UI. Please tell me what do I like? - How to specify charset - String embedded in a page how to generate CP932 (UTF-8 instead) - How to decode the parameters posted thank you.

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lucius docs
by Max Cantor 19 Apr '11

19 Apr '11

are there any blog posts or entries or good sample code to see the syntax for lucius? is it the same as LESS but with #{xxx} interpolation? max

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What does Persist's PersistUpdate datatype do?
by Ian Duncan 17 Apr '11

17 Apr '11

I'm fiddling around a bit with the Persist library and wondering what the PersistUpdate datatype does. From what I can gather, it looks like Update replaces the value, add will add to the current value if it is an integer or double, and subtract, multiply, and divide perform their respective operations. Is this correct, or is there something else to these types? Thanks! Ian Duncan

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problem with yesod, persist and enumerations
by Chris Casinghino 16 Apr '11

16 Apr '11

Hi all, I'm running into significant compile-time performance problems with a relatively simple database. This email describes a small example using a default project from the yesod scaffolding tool. Trying to compile the project causes ghc to consume several GB of memory on my system (eventually I have to kill it). I'm running GHC 7.0.3 and the current yesod beta. It's definitely possible that I'm doing something very stupid - any help would be appreciated. The example just involves adding one table to a default project's database. Suppose I want to add a table with 15 columns, each holding a US State or Nothing (a little silly, but in my real application the data is more interesting). To do this, I'll make a datatype to list the US states, give it a PersistField instance with some help from the Enum typeclass, and add the table. In the Model.hs file, I add an import line: > import Database.Persist.Base And then I define my representation of the US State codes: > data USStateCode = > AL | AK | AS | AZ | AR | CA | CO | CT | DE | DC > | FM | FL | GA | GU | HI | ID | IL | IN | IA | KS | KY | LA | ME > | MD | MA | MI | MN | MS | MO | MT | NE | NV | NH | NJ | NM | NY > | NC | ND | MP | OH | OK | OR | PW | PA | PR | RI | SC | SD | TN > | TX | UT | VT | VI | VA | WA | WV | WI | WY > deriving (Read, Show, Eq, Ord, Enum) > > instance PersistField USStateCode where > toPersistValue = PersistInt64 . toEnum . fromEnum > > fromPersistValue (PersistInt64 a) = Right $ toEnum $ fromEnum a > fromPersistValue _ = Left "error" > > sqlType _ = SqlInteger And I add the table to the bottom of my entities file: > MyTable > st1 USStateCode Maybe > st2 USStateCode Maybe > st3 USStateCode Maybe > st4 USStateCode Maybe > st5 USStateCode Maybe > st6 USStateCode Maybe > st7 USStateCode Maybe > st8 USStateCode Maybe > st9 USStateCode Maybe > st10 USStateCode Maybe > st11 USStateCode Maybe > st12 USStateCode Maybe > st13 USStateCode Maybe > st14 USStateCode Maybe > st15 USStateCode Maybe Making these changes to a default project and then compiling causes the problems I described above. Can someone fill me on on a better way to add a table holding some enumerated data? Thanks! --Chris

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Yesod performance
by Aur Saraf 15 Apr '11

15 Apr '11

First, the nice people at #haskell (specifically it was <sm>, but there were many other helpful people there like <ksf> and others whose names I won't remember) made me swtich from fastcgi to warp. I didn't think it would be relevant, since my performance problems were all memory-consumption-related, but it turned out to speed my code by orders of magnitude. Everybody switch to warp! :-) Second, I've been thinking about the performance bounds of a Yesod app. As in, given an app that has no leaks etc', where can I expect it to perform better than imperative languages I'm familiar with, where can I expect it to perform worse? The biggest limits imposed by Yesod that I thought about were: * [Char] - not in Yesod 0.8 * Persistent always takes a full row - shouldn't matter much in practice, especially if persistent is lazy and doesn't parse columns I don't care about * No joins in DB - being solved as we speak * All page must be generated before it is sent if we plan to use Widgets -- Well, this one is interesting. It seems to be very much against Haskell nature, that is so lazy and nice, and I think in my code it might actually make performance difference. So I thought -- isn't it possible to extend Hamlet to work in an Iteratee too? What do I mean? Something like: rows <- selectEnum ... hamletAction [$hamlet| <html> <head> <body> $for row <- rows <p> #{rowDescription row} <p .fineprint> (c) Aur Saraf etc' etc' That would expand to a monadic action that creates chunks of HTML while reading the rows Enumerable. Is there any serious technological problem with this approach? Or just choosing a nice extension of Hamlet that would allow running monadic actions in it like functions are allowed today, without affecting the simplicity of the API? Cheers, Aur PS Michael, is it possible in Yesod to have two selectEnum-s "running" at the same time? Otherwise you'd only be able to work with one query at a time in this way...

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Tracking Yesod Book updates
by vagif.verdi＠gmail.com 15 Apr '11

15 Apr '11

Is there a way to show last updated date/time of yesod book chapters ? Maybe in the TOC or on the pages themselves. It's kind of hard to know what have changed or added. Regards, Vagif Verdi

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parse error with yesod's email authentication
by Chris Casinghino 14 Apr '11

14 Apr '11

Hi all, I'm having some trouble with the email authentication that the yesod scaffolding tool sets up for me. I'm using the Yesod 0.8 beta and ghc 7.0.3. I created a new yesod with the yesod tool and a sqlite database. I immediately compiled it (cabal configure && cabal build) without changing anything and ran the "test" binary. I navigated to the webpage and tried to register using my email address. The email I got contains this link: http://localhost:3000/auth/page/email/verify/EmailId%20%7BunEmailId%20=%20P… But when I click it, the webpage reports: Internal Server Error Prelude.read: no parse Do I need to set something else up to get this working? Thanks for your help. I'm loving yesod so far (already deployed my first Yesod app! Luckily it doesn't need auth :) --Chris

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ANNOUNCE: TCache 0.8
by Alberto G. Corona 14 Apr '11

14 Apr '11

Tired of your persistence layer? Take persistence the haskelll way. Besides the backward compatible stuff, TCache now defines persistent STM variables (DBRef's) that leverages the traditional haskell reference syntax to perform fast in-memory database transactions and inter-object references. It includes indexing, triggers and an straightforward pure-haskell query language based on record field relations. http://hackage.haskell.org/package/TCache-0.8.0.2 This version includes a lot of changes and must be considered beta. Please submit any bugs, comments and so on. Cheers!

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