June 2011 - web-devel

Re: [web-devel] Auto-discard notification
by Michael Snoyman 09 Jun '11

09 Jun '11

> From: Hehe Nicht <zerstroyer(a)googlemail.com> > To: web-devel(a)haskell.org > Date: Thu, 9 Jun 2011 11:26:14 +0200 > Subject: withStmt function > Could someone explain the withStmt function from Persist.Raw to me? > Here is an example i was toying with: > >>{-# LANGUAGE QuasiQuotes, TypeFamilies, GeneralizedNewtypeDeriving, TemplateHaskell, OverloadedStrings #-} >>import Database.Persist >>import Database.Persist.Base >>import Database.Persist.Sqlite >>import Database.Persist.GenericSql.Raw >>import Control.Monad.IO.Class (liftIO) >> >>main :: IO () >>main = withSqliteConn ":memory:" $ runSqlConn $ do >> _ <- execute "CREATE TABLE cities (name varchar(80),location point);" ([]::[PersistValue]) >> _ <- execute "INSERT INTO cities VALUES ('SanFrancisco','(100.0,100.9)');" ([]::[PersistValue]) >> _ <- execute "INSERT INTO cities VALUES ('New York','(1.0,10.9)');" ([]::[PersistValue]) >> query <- withStmt "SELECT name, location FROM cities;" ([]::[PersistValue]) (id) >> liftIO $ print query > > which prints "Just [PersistText "SanFrancisco",PersistText > "(100.0,100.9)"])". So how do i get the rest of the rows? Do i have to > pass a different function as the last argument to withStmt? > Thanks in advance. > > > The function provided by withStmt returns one row at a time, until it exhausts the input and returns a Nothing. I'll try to write a "cookbook recipe" for the next cookbook installment describing that. Michael

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Re: [web-devel] Auto-discard notification
by Michael Snoyman 09 Jun '11

09 Jun '11

> From: Jakob Vidmar <jakob.vidmar(a)gmail.com> > To: web-devel(a)haskell.org > Date: Thu, 9 Jun 2011 08:09:53 +0200 > Subject: [OSX] Cabal installation error > Hi all! > I have GHC 7.0.3 installed, along with the latest version of > Haskell Platform. When I tried installing yesod I received > the following error: > Yesod/Auth.hs:233:10: > Not in scope: type constructor or class `Message' > cabal: Error: some packages failed to install: > yesod-0.8.2 depends on yesod-auth-0.5.0 which failed to install. > yesod-auth-0.5.0 failed during the building phase. The exception was: > ExitFailure 1 > I tried installing yesod-auth separately, but cabal insisted on > installing version 0.6 (and that installed successfully). Any > suggestions? > I just uploaded a new version with stricter version bounds. Can you try "cabal update && cabal install yesod" and see if that works? Thanks, Michael

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safety of Data.Ascii.unsafeFromString
by Max Cantor 09 Jun '11

09 Jun '11

just how unsafe are the unsafeXXX functions in Data.Ascii? IS it just that you might get a runtime exception or could they do some more serious damage somehow? max

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GGHandler, PersistBackend, and MonadPlus
by Jeremy Hughes 09 Jun '11

09 Jun '11

Hi, Could GGHandler be made an instance of MonadPlus, and PersistBackend have MonadPlus in its context? I have found both to be useful. Jeremy diff from yesod-core-0.8.2/Yesod/Handler.hs 123c123 < import Control.Monad (liftM, join, MonadPlus) --- > import Control.Monad (liftM, join) 249c249 < deriving (Functor, Applicative, Monad, MonadPlus, MonadIO, MonadControlIO) --- > deriving (Functor, Applicative, Monad, MonadIO, MonadControlIO) diff from persistent-0.5.1/Database/Persist/Base.hs 54a55,56 > import Control.Monad > 303c305 < class Monad m => PersistBackend m where --- > class MonadPlus m => PersistBackend m where diff from persistent-0.5.1/Database/Persist/GenericSql.hs 34c34 < import Control.Monad (liftM, unless) --- > import Control.Monad (liftM, unless, MonadPlus) 63c63 < instance MonadControlIO m => PersistBackend (SqlPersist m) where --- > instance (MonadPlus m, MonadControlIO m) => PersistBackend (SqlPersist m) where diff from persistent-0.5.1/Database/Persist/GenericSql/Raw.hs 22a23 > import Control.Monad 25c26 < deriving (Monad, MonadIO, MonadTrans, Functor, Applicative, MonadControlIO) --- > deriving (Monad, MonadIO, MonadTrans, Functor, Applicative, MonadControlIO, MonadPlus) diff from persistent-mongoDB-0.2.2/Database/Persist/MongoDB.hs 28a29 > import Control.Monad (MonadPlus) 37c38 < deriving (Monad, Trans.MonadIO, Functor, Applicative) --- > deriving (Monad, Trans.MonadIO, Functor, Applicative, MonadPlus) 121c122 < instance (DB.DbAccess m, DB.Service t) => PersistBackend (MongoDBReader t m) where --- > instance (DB.DbAccess m, DB.Service t, MonadPlus m) => PersistBackend (MongoDBReader t m) where

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Fwd: xml-types IsString instance for Name causes crashes
by Dmitry Olshansky 09 Jun '11

09 Jun '11

> There is no language I've ever heard of where you can cause a > program to crash at *runtime* because of the particular characters > you include in a string literal in your source code. Please don't make > Haskell the first. That would be very ironic. This possibility is provided by "OverloadedStrings" extension, not by instance for Name. >From other side I suppose that any implicit transformation in other languages could lead the same problems. Personally, I don't see difference between typo in >n = name "foo}bar" and >n = "foo}bar" But I prefer the second because I have no additional function names in my memory. I consider IsString instance just as standard conversion from String without any parameters. 2011/6/9 Yitzchak Gale <gale(a)sefer.org> > >> Since the whole idea of xml-types is for it to be a > >> unifying standard, I'd like to see it usable in that kind > >> of environment, too. > > > It is usable in such an environment -- simply do not > > use the IsString instance. > > Once you have the Name type rather than just Text - > which is useful for people needing namespaces - > the IsString instance is important to keep code from > becoming really awkward. > > Perhaps the real problem here is including Clark > notation in the IsString instance. Clark notation is > very nice, but it doesn't really belong in the IsString > instance. Clark notation could be a function, or a > quasi-quoter. Perhaps the client library should be > allowed to decide. > > But if it is included in the IsString instance, it > absolutely cannot raise an asynchronous exception. > That is a serious bug. > > >> In addition, I have already pointed out that semantically > >> it doesn't make sense for a fromString implementation > >> to return _|_. And it is easy to make a small change > >> to the current implementation to avoid that. > >> > >> So let me turn the question around. Is there a compelling > >> reason why, in some use case, the fromString must > >> return _|_, rather than returning some text that will allow > >> the application to handle the situation itself? > > > The string "foo}bar" is invalid; it must *never* be converted to a > > Name. Doing so would cause silent, unpredictable failures which cannot > > be tested for. > > '}' `elem` name would do the trick nicely. > > The Name type already produces invalid XML. A client library > that wants to avoid invalid names must already check for them. > If a typo in Clark notation were another way to create invalid > XML that wouldn't change anything. > > But if that really bothers you, let's discuss the many other > options for introducing Clark notation other than in the IsString > instance. > > > IsString does not support reporting parse errors; > > Right, and it shouldn't. IsString is just a way of giving a different > string type, like ByteString or Text, to Haskell's string literal syntax. > There is no parsing to do beyond what the compiler already does. > Any IsString instance should just take the contents of the string > literal and incorporate it directly into the string type. > > There is no language I've ever heard of where you can cause a > program to crash at *runtime* because of the particular characters > you include in a string literal in your source code. Please don't make > Haskell the first. That would be very ironic. > > > if you're very concerned about it, I could add a flag like > > "NoIsString" which disables that particular instance. You could enable > > it in your build scripts. > > I wouldn't use that flag. I need and use the IsString instance. > The instance must be defined in the module that defines the type. > > Thanks, > Yitz > > _______________________________________________ > web-devel mailing list > web-devel(a)haskell.org > http://www.haskell.org/mailman/listinfo/web-devel >

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Confusing double use of chooseRep in runHandler
by Tyson Whitehead 09 Jun '11

09 Jun '11

I believe there may be an unneeded pass through chooseRep in at the end of runHandler in the HCContent branch of the content case construct HCContent status a -> do (ct, c) <- liftIO $ chooseRep a cts return $ YARPlain status (headers []) ct c finalSession The chooseRep instance will just be id as a is already of type ChooseRep. While I doubt there would be any performance benefit, as I would hope it is optimized out, it did cause me some confusion while reading to code, so think it would be worth removing for clarity. I've attached a patch for this. Cheers! -Tyson

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being able to have multiple selections, via selectField
by Michael Litchard 08 Jun '11

08 Jun '11

What I'm looking for can be seen on this page: http://api.jquery.com/selected-selector/ I'm wondering if selectField is the correct approach. It seems I can only have one selection with selectField. If not, what is my best option?

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yesod vs rails 3 asset pipeline
by Max Cantor 07 Jun '11

07 Jun '11

all my rails friends are shitting themselves about some new "asset pipeline" which takes your individual css and js files and minifies and combines them into a single file to send to clients. as far as I can tell, this brand-new-killer-omfg-feature is what yesod has been doing from the beginning. what am I missing? max

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[Yesod] Nesting widgets
by Aren Olson 07 Jun '11

07 Jun '11

In Yesod, if I have two Widgets, how can I 'nest' the content of one widget inside one of the tags of the other? In effect, I want to be able to do something like widget <- do addHamlet [hamlet| some html |] addCassius [cassius| some css |] otherwidget <- do addHamlet [hamlet| <div ${widget} ] and end up with the body contents from widget inside otherwidget's <div> tag, while widget's cassius data still ends up in the page's <head> as normal. I can't find any documentation or examples of this, and nothing I tried would compile. Is this doable? If so, how? Thanks, -Aren

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API change request for WAI
by Kazu Yamamoto 07 Jun '11

07 Jun '11

Hello, I would like ask to change WAI API a bit. Please include the following data constructor for Response: ResponseIO Status ResponseHeaders (Socket -> IO Bool) # Please choose better name than ResponseIO The function whose type is Socket -> IO Bool is to send a HTTP body to the socket and returns keepalive-or-not. This opens possibilities to find a better sending scheme than that which Warp adopts by default. I'm implementing a classical web server library on WAI (wai-app-file-cgi). It sends files to clients with ResponseFile. Warp uses the sendfile library for ResponseFile. The sendfile library uses (unnecessary) hSeek and hFileSize which call system calls. System calls causes context switches. Since GHC7's IO manager uses a single kernel thread, all Haskell threads stops. Calling system calls gives significant performance impact. ResponseIO enables to choose a function which sends files with minimum system calls for WAI users. I have already implemented this both in wai and warp, and confirmed that this works well. --Kazu

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