April 2010 - web-devel

BlazeHtml: a question about API design
by Jasper Van der Jeugt 25 Apr '10

25 Apr '10

Hey web-devel mailing list, I'm currently working on the BlazeHtml HTML combinator library, and currently a bit stuck on a piece of API design, for which I need some community feedback. I'll try to explain the problem here as clear as possible. The base idea is, for an HTML combinator library, that you provide combinators that the end user can use to "combine" his document. More specifically, we would have combinators for every HTML element. So, say you have the regular div tag. This would be, in our library, Text.Blaze.Html.Strict.div. That makes sense, but it seems possible that a user wants to use a div as a leaf node (e.g. `<div />`). So there are two possible signatures for `div`: div :: Html -- An empty div element. div :: Html -> Html -- The argument is the content of the div element. I'm not sure what we want to do in that case. I so far see two major options: Option 1: We can provide leaf and non-leaf combinators for every tag. I'm not sure if this is overkill or not, but it is, for example not forbidden to have content in an `<img>` tag. We could have these functions in Text.Blaze.Html.Strict and Text.Blaze.Html.Strict.Leaf, for instance. But it must be kind of annoying for the end user to have to write `L.div` instead of just `div`. On the other hand, if we put the *common* uses for the tags (e.g. `img` as leaf, `div` as non-leaf) in the main module, we would get a very inconsistent mess, I assume. So this solution would include: - a module of html combinators as non-leaf elements - a module of html combinators as leaf-elements - the possibility for the end-user to import and qualify them as he/she sees fit; or - add a module with the most common uses and re-export the combinators Option 2: We could only support parent nodes (of the type `Html -> Html`), and introduce another combinator: (/>) :: Html (/>) = mempty I have chosen `/>` here because it resembles the end of a leaf HTML tag (e.g. `<img />`). Then, we would introduce a custom rule. {-# RULES "tag/empty" forall x y. tag x y (/>) = leaf x #-} The `y` here is the closing tag, we pass it as an argument for performance reasons, and you can safely ignore it. This code results in the fact that if we write img (/>) somewhere in our template, it would be rendered to `<img></img>` when we don't pass `-fenable-rewrite-rules` to the compiler, and `<img />` otherwise. Note that `-O` implies `-fenable-rewrite-rules`. I'm not sure about this solution either, because it sort of feels like a (slightly elegant) hack. I have my doubts with both options, but I would tend to go for (1), because (2) feels more unstable. Anyway, feedback and more ideas would be appreciated :-) Kind regards, Jasper Van der Jeugt

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Re: [web-devel] alpha release: my thesis
by Chris Eidhof 24 Apr '10

24 Apr '10

Hey Thomas, I think you need to checkout the following packages from github and cabal-install them: chriseidhof/fclabels chriseidhof/salvia chriseidhof/salvia-protocol chriseidhof/regular-web chriseidhof/Basil And then you could checkout my thesis repository and do a "cd quiz; ghci Quiz.lhs; main". I'm sure that I've forgotten something, just let me know if you run into problems and I'll fix the instructions. -chris On 23 apr 2010, at 21:14, Thomas Hartman wrote: > I see there's a lot of stuff on github. Yah! > > Could you give the command(s) for > > -- checkout > -- cabal install > -- run the quiz sample app > > cheers, thomas. > > > On Fri, Apr 23, 2010 at 6:53 AM, Chris Eidhof <chris(a)eidhof.nl> wrote: >> Hm, the link didn't render correctly because of the web-devel footer. The correct link is: >> >> http://eidhof.nl/thesis/thesis-alpha.pdf >> >> Thanks, >> >> -chris >> >> On 23 apr 2010, at 14:40, Chris Eidhof wrote: >> >>> Hey everyone, >>> >>> Next week I'll be handing in my thesis, which is titled "Web development in Haskell". In my thesis I discuss three libraries that I've developed: one for data modeling (and persistency), one for continuation-based web programming and a library for generic views. The thesis starts with a small example that shows how these libraries play together. >>> >>> If anybody feels like reading it, I've uploaded the current version [1]. If there's anything that's unclear: it's not your fault, but probably lousy writing from me. Comments are very much appreciated and can be emailed to me. >>> >>> After finishing my thesis, I plan to build a nice website and tutorial for this framework, and prepare everything to release it on hackage. It'll probably take some time though, but I'll keep this list updated. >>> >>> -chris >>> >>> [1]: http://eidhof.nl/thesis/thesis-alpha.pdf___________________________________… >>> web-devel mailing list >>> web-devel(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/web-devel >> >> _______________________________________________ >> web-devel mailing list >> web-devel(a)haskell.org >> http://www.haskell.org/mailman/listinfo/web-devel >> > > > > -- > Need somewhere to put your code? http://patch-tag.com > Want to build a webapp? http://happstack.com

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alpha release: my thesis
by Chris Eidhof 23 Apr '10

23 Apr '10

Hey everyone, Next week I'll be handing in my thesis, which is titled "Web development in Haskell". In my thesis I discuss three libraries that I've developed: one for data modeling (and persistency), one for continuation-based web programming and a library for generic views. The thesis starts with a small example that shows how these libraries play together. If anybody feels like reading it, I've uploaded the current version [1]. If there's anything that's unclear: it's not your fault, but probably lousy writing from me. Comments are very much appreciated and can be emailed to me. After finishing my thesis, I plan to build a nice website and tutorial for this framework, and prepare everything to release it on hackage. It'll probably take some time though, but I'll keep this list updated. -chris [1]: http://eidhof.nl/thesis/thesis-alpha.pdf

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Simple mime-type package
by Michael Snoyman 23 Apr '10

23 Apr '10

Hi all, In Yesod, I have very modest needs when it comes to mime-types. Basically, I want: * a data type to represent mime-types * convert a string to a mime-type * convert a mime-type to a string * determine mime-type of a file based on extension I've stuck all this in a simple module: Web.Mime[1]. However, it seems like this is a perfect candidate for a dedicated package. So I wanted to ask: 1) Is there a package out there- with minimal dependencies- that supplies this functionality? 2) If not, would anyone else find it useful if I split this off into its own package? Michael [1] http://github.com/snoyberg/yesod/blob/ver0.2/Web/Mime.hs

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Re: [web-devel] Simple mime-type package
by Michael Snoyman 22 Apr '10

22 Apr '10

A quick look through the docs didn't find a similar module. Do you know where in particular it might be? I'm not familiar with the gitit codebase at all. Michael On Wed, Apr 21, 2010 at 1:24 PM, Thomas Hartman < thomashartman1(a)googlemail.com> wrote: > there's something like this in gitit I believe. > > On Wed, Apr 21, 2010 at 9:56 AM, Michael Snoyman <michael(a)snoyman.com> > wrote: > > Hi all, > > In Yesod, I have very modest needs when it comes to mime-types. > Basically, I > > want: > > * a data type to represent mime-types > > * convert a string to a mime-type > > * convert a mime-type to a string > > * determine mime-type of a file based on extension > > I've stuck all this in a simple module: Web.Mime[1]. However, it seems > like > > this is a perfect candidate for a dedicated package. So I wanted to ask: > > 1) Is there a package out there- with minimal dependencies- that supplies > > this functionality? > > 2) If not, would anyone else find it useful if I split this off into its > own > > package? > > Michael > > [1] http://github.com/snoyberg/yesod/blob/ver0.2/Web/Mime.hs > > _______________________________________________ > > web-devel mailing list > > web-devel(a)haskell.org > > http://www.haskell.org/mailman/listinfo/web-devel > > > > > > > > -- > Need somewhere to put your code? http://patch-tag.com > Want to build a webapp? http://happstack.com >

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Hamlet & Haml
by Gour 22 Apr '10

22 Apr '10

Hello! Many/Some RoR folks swear at Haml/Sass (http://haml-lang.com/) and I see there is Hamlet project at Github (http://github.com/snoyberg/hamlet) saying "Haml-like template files that are compile-time checked", so I'm curious if it targets to be Haml-compatible or just "haml-like" ? Sincerely, Gour -- Gour | Hlapicina, Croatia | GPG key: F96FF5F6 ----------------------------------------------------------------

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Question about happstack
by Kyle Murphy 21 Apr '10

21 Apr '10

I had downloaded and was experimenting with a simple Happstack based pastebin a while ago, and was making reasonable progress in figuring out Happstack and how to go about handling various situations. I hadn't touched the code in a while and decided I wanted to eperiment with it last night, so I made a few tweaks and attempted to re-compile it. Now, I'm finding that neither my modified version, nor the original version I downloaded will compile, as they complain about not being able to find an instance of MonadIO for (ServerPartT IO). I also tried writing up a trivial server based on the documentation provided by Happstack itself, and that also fails to compile complaining about no instance found for MonadIO (ServerPartT IO). Specifically the error seems to be triggered by the use of liftIO anywhere inside a ServerPartT monad. Looking at the source code for happstack-server, I can see in Happstack.Server.SimpleHTTP that the GeneralizedNewtypeDeriving pragma is set, and that in the newtype for ServerPartT it has deriving MonadIO. Why can't ghc seem to find the MonadIO instance for ServerPartT, when ServerPartT is declared as deriving it? It also seems strange that this just started happening recently. I've upgraded a number of packages recently, but I can't say for sure what I changed since the last time I was able to compile something based on happstack successfully. Is it possible that some change with mtl or some other package is causing this error? Near as I can tell, this is occurring in happstack-server-0.4.1, although since I'm away from my personal computer right now I can't provide the versions for any of the other packages. If anyone would like further details I can provide them late tonight when I get home, but till then the best I can do is provide the source of one of the programs I attempted to compile (hosted interestingly enough by a later build of the same code): http://tenletters.org/1 -R. Kyle Murphy -- Curiosity was framed, Ignorance killed the cat.

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ANN: web-routes now on hackage
by Jeremy Shaw 21 Apr '10

21 Apr '10

Hello, I have uploaded web-routes to hackage. Now we can work on writing some tutorials/documentation so other people know what it is and why it is awesome :) I'll make a more formal announcement on haskell / haskell-cafe when I have something informative to say about it to strangers. - jeremy

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happstack + hamlet
by Jeremy Shaw 20 Apr '10

20 Apr '10

Hello, As an experiment I modified the hamlet demo to use happstack. Was pretty trivial. I just added, -- happstack changes main :: IO () main = simpleHTTP nullConf $ liftIO $ hamletToResponse renderUrls $ template person hamletToResponse :: (Monad m) => (url -> String) -> Hamlet url m () -> m Response hamletToResponse showFn hamlet = do msg <- hamletToText showFn hamlet return $ toResponse_ (B.pack "text/html; charset=UTF-8") (T.encodeUtf8 msg) toResponse_ :: B.ByteString -> L.ByteString -> Response toResponse_ contentType message = let res = Response 200 M.empty nullRsFlags message Nothing in setHeaderBS (B.pack "Content-Type") contentType res The toResponse_ function really belongs in happstack anyway. I am going to add that right now. Normally we would add a ToMessage instance, so you could do: simpleHTTP nullConf $ template person But that won't work for two reasons: 1. we would need a way to pass in the (url -> String) function 2. the toResponse type signature does not allow for the monadic requirements of hamletToText But that is really just an issue with ToMessage class (and why I don't really like that type class much). I would like to make hamletToResponse (or something similar) available to happstack users. I think I probably need to make a new package, happstack-hamlet, to stick it in. I wonder if there is anything else useful that could go in there. I could add some additional instances, such as: mapHamlet :: forall a b url m n. (Monad m) => (m a -> m b) -> Hamlet url m a -> Hamlet url m b mapHamlet f m = Hamlet $ \showFn seed iteratee -> f' (runHamlet m showFn seed iteratee) where f' :: m (Either seed (a, seed)) -> m (Either seed (b, seed)) f' m = do e <- m case e of (Left s) -> return (Left s) (Right (a, seed)) -> do b <- f (return a) return (Right (b, seed)) instance (ServerMonad m) => ServerMonad (Hamlet url m) where askRq = liftHamlet askRq localRq f = mapHamlet (localRq f) instance (FilterMonad r m) => FilterMonad r (Hamlet url m) where setFilter = liftHamlet . setFilter composeFilter = liftHamlet . composeFilter getFilter = mapHamlet getFilter instance (WebMonad a m) => WebMonad a (Hamlet url m) where finishWith = liftHamlet . finishWith So that you could use some of the functionality of the ServerMonad, etc, in your Hamlet templates. But I am not clear how that would be useful yet. - jeremy Anyway, the full code is attached.

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Re: [web-devel] Question about happstack
by Kyle Murphy 20 Apr '10

20 Apr '10

I'm not sure I understand your question. I've got the happstack-server package installed, as well as various other happstack packages. In fact I used cabal to download the source for happstack-server which contains the newtype declaration for ServerPartT in order to verify that it does in fact declare a MonadIO instance for ServerPartT (which it does by deriving it as opposed to explicitly declaring it). It rather thoroughly puzzles me that GHC seems to think there's no MonadIO instance for ServerPartT, but I can go take a look at the source code and see it declared. I can really only think of two possible explanations aside from a defect in GHC itself, which is that either there's something wrong with the way ServerPartT is being exported/imported, or there's some kind of mismatch between the MonadIO declaration in the version of mtl I'm using, and whatever is being used to build happstack-server. Of course by the same token I'm a pretty big newbie with Haskell, so there's probably quite a few other possible explanations that I can't even begin to think of. -R. Kyle Murphy -- Curiosity was framed, Ignorance killed the cat. On Tue, Apr 20, 2010 at 13:07, davean <davean(a)xkcd.com> wrote: > I'm away from my computer right now also, but I seem to recall having this > issue myself at one point; do you also have happstack? > > On Tue, Apr 20, 2010 at 10:02 AM, Kyle Murphy <orclev(a)gmail.com> wrote: > >> I had downloaded and was experimenting with a simple Happstack based >> pastebin a while ago, and was making reasonable progress in figuring out >> Happstack and how to go about handling various situations. I hadn't touched >> the code in a while and decided I wanted to eperiment with it last night, so >> I made a few tweaks and attempted to re-compile it. Now, I'm finding that >> neither my modified version, nor the original version I downloaded will >> compile, as they complain about not being able to find an instance of >> MonadIO for (ServerPartT IO). I also tried writing up a trivial server based >> on the documentation provided by Happstack itself, and that also fails to >> compile complaining about no instance found for MonadIO (ServerPartT IO). >> Specifically the error seems to be triggered by the use of liftIO anywhere >> inside a ServerPartT monad. >> >> Looking at the source code for happstack-server, I can see in >> Happstack.Server.SimpleHTTP that the GeneralizedNewtypeDeriving pragma is >> set, and that in the newtype for ServerPartT it has deriving MonadIO. Why >> can't ghc seem to find the MonadIO instance for ServerPartT, when >> ServerPartT is declared as deriving it? >> >> It also seems strange that this just started happening recently. I've >> upgraded a number of packages recently, but I can't say for sure what I >> changed since the last time I was able to compile something based on >> happstack successfully. Is it possible that some change with mtl or some >> other package is causing this error? >> >> Near as I can tell, this is occurring in happstack-server-0.4.1, although >> since I'm away from my personal computer right now I can't provide the >> versions for any of the other packages. If anyone would like further details >> I can provide them late tonight when I get home, but till then the best I >> can do is provide the source of one of the programs I attempted to compile >> (hosted interestingly enough by a later build of the same code): >> http://tenletters.org/1 >> >> -R. Kyle Murphy >> -- >> Curiosity was framed, Ignorance killed the cat. >> >> _______________________________________________ >> web-devel mailing list >> web-devel(a)haskell.org >> http://www.haskell.org/mailman/listinfo/web-devel >> >> >

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