Alson Kemp

Bodo Nauman (http://www.naumann.cc/) got Turbinado to build with GHC 6.10 (after forcing me to fix a bunch of recently added bugs…).  Details are here.  There’s currently an issue with the crypto Hackage package which doesn’t build with GHC 6.10**.  Fortunately, the darcs version of crypto builds fine.

Bodo beat me by a couple of days to an updated “How to install Turbinado” post.  Since v0.5 is freshly minted (ahem… and debugged) (and includes cookies, cookie sessions (lifted from Michael Snoyman’s hweb), a Rails-like respondTo function, …), I’ll post an update in a day or two.

Adolfo Builes also has started to replicate a Rails tutorial in Turbinado, so I hope I can point you to his results soon.

** The crypto build fails when building some test applications.  What’s weird is that “cabal install” installs the test applications into the bin directory.  Why would I want test applications in /usr/local/bin?  I don’t see a Cabal flag for “just build the libraries”…

From Happstack:

“[If HApps doesn't do anything...] the project will eventually be superceded by other Haskell frameworks like Turbinado which are not nearly as innovative”

Woohoo!  People are talking about Turbinado!

err… Wait! Turbinado is being dissed!

Turbinado vs. HApps

Each project is valid and valuable, so I’m hesitant to get to far into a X vs. Y discussion, but here are some aspects that I thought about when evaluating HApps and developing Turbinado:

• Turbinado is built on top of Nicklas Broberg‘s HSP/HSPR, which I consider to be an innovative-port of ASP to Haskell…
• HApps is a much bigger project with many more features; Turbinado is small and needs your help [shameless plug: help here].
• HApps seems more like a library of really useful functions which is very flexible; Turbinado is more like a web app framework and provides a web server along with defined mechanisms for adding Controller, Views and Components.  Convention over Configuration = different styles, not better styles.
• HApps seems less than simple (see here); Turbinado is all about simple (see here)
• HApps has an aversion to relational databases; Turbinado observes that lots of people use relational databases and supports them.

Turbinado vs. HApps, again

To me, it seems as though the choice between HApps and Turbinado depends more on orientation than on functionality.  If you are interested in: opposing RDMBSs, but are into something like Sinatra, then HApps is probably the best choice; if you’re interested in writing web apps in the style of Ruby On Rails, then Turbinado (though young and pretty) may be the best choice, especially given the simplicity of building Turbinado (newly cabal installable!  to be described in a forthcoming post with tutorials, install details, singing, dancing, high kicks, etc).

Here’s To Success

Most successful languages have more than one web framework, so I hope for success for both HApps and for Turbinado. They’re very different frameworks and serve very different needs. The Haskell community would be well served if both frameworks survived and thrived.  As Merb and Rails have demonstrated, cross-pollination is excellent; the stronger HApps and Turbinado are, the more they can benefit each other.

See also: 2009-The Year Of Hackage and A Plea For Cabal-install

I’m finally getting Turbinado updated for GHC 6.10 and I owe a huge debt to the cabal-install team (my preferred currency for debt payment is beer).  Turbinado is a bitch to install by hand because it depends on specific version of various packages.  One minor rev off and everything explodes.

So I’ve been bouncing between 3 machines working on Turbinado and trying to get the build cleaned up.  Once cabal-install is installed, it’s a simple “cabal install” to get all dependencies downloaded and built.  Much better than setting up a local packages directory, downloading 10 packages, trying to get the install order figured out and trying to remember which of the 10 packages is installed or not.

It’s fantastic that GHC is finally getting a package and build manager.

If you haven’t played with cabal-install, you should:

darcs get --partial http://darcs.haskell.org/cabal-install/
cd cabal-install
sh bootstrap.sh
ln -s ~/.cabal/bin/cabal ~/bin/cabal  ### or somewhere else useful
cabal update

My only want for cabal-install is for it to install executables somewhere more useful than ~/.cabal.  But that’s a minor gripe…

Turbinado continues to evolve:

Turbinado (http://www.turbinado.org) is an easy 
to use Model-View-Controller-ish web framework for Haskell.

The source for the framework can be found at:
http://github.com/alsonkemp/turbinado

The source for the website turbinado.org can be found at:
http://github.com/alsonkemp/turbinado-website
(see the /App directory for the code for www.turbinado.org)

Release 0.4 contains:
* A dramatically improved ORM (or Type-Relation Mapper) 
   which handles foreign keys.  Still PostgreSQL only at this point.
* All dependencies in tmp/dependencies to ease building the application.
* In code documentation (not complete, but starting).
* Documentation (see http://turbinado.org/Architecture).

Release 0.5 will focus on:
* Ease of installation!
* Moving to GHC 6.10 (whenever Debian shifts).  Diego Eche 
   provided a port from plugins to ghc-api.
* Additional functionality (e.g. sessions, authentication, etc).
* Tutorials.

Turbinado has the beginnings of a database ORM built in.  I’m hoping to make it super simple to interact with a relational DB, but I’m bumping up again import cycles. Ticket about import cycles here.

The Problem

import qualified App.Models.PageModel as Page
import qualified App.Models.CommentModel as Comment
 
someFn = do p  <- Page.find "tutorial"  -- find using a primary key of "tutorial"
            cs <- Page.findAllChildComment p
            let c = head cs
            p2 <- Comment.getParentPage c

Yeah, could be prettier (hmm… maybe Rails’ pluralization is good after all…), but that’s a pretty nice way to access related Pages and Comments in a SQL database. What doesn’t work, though are the imports. Since Page.findAllChildComment returns Comments, PageModel needs to import CommentModel. But, since CommentModel also uses the Page type, CommentModel needs to import PageModel. And thus the cycle begins…

Fix #1

The custom seems to be to push the data types out to a Types.hs file.

Assuming that Types.hs is imported and exported by all Models, then the following doesn’t work:

import qualified App.Models.PageModel as PageModel
import qualified App.Models.CommentModel as CommentModel
 
someFn = do let p = Page {title = "blah", content = "ack", _id = "page1"}
            PageModel.insert p False

Is the Page type the one from PageModel or from CommentModel? Both models export the Page type.

Update: As Twan points out in the Comments, the above would work if I were happy to do either of:

  let p = PageModel.Page {title = "blah", content = "ack", _id = "page1"}
  let p = CommentModel.Page {title = "blah", content = "ack", _id = "page1"}

Perhaps it’s unreasonable of me, but I want to be able to refer to the type without being forced to refer to the module. Besides, this post is really a gripe about import cycles, so I can’t have Fix #1 work and still gripe…

Fix #2

Push the data types out to a Types.hs file, but don’t export Types from the Models. Now you have to explicitly import Types whenever you’re using a Model:

import App.Models.Types   -- I'm not pretty...
import qualified App.Models.PageModel as PageModel
import qualified App.Models.CommentModel as CommentModel
 
someFn = do let p = Page {title = "blah", content = "ack", _id = "page1"}
            PageModel.insert p False

Now Page is clearly taken from App.Models.Types. But my delicate aesthetic sensibilities are offended.

But wait! We’re still broken! Since PageModel and CommentModel may use functions from each other, import cycles can still be produced. For example, Page.findAllChildComment uses a function from CommentModel:

instance HasChildComment (Page) where
    findAllChildComment p = CommentModel.findAllWhere "page_id = ?" [HDBC.toSql $ _id p]

Now if CommentModel needs a function from PageModel, then an import cycle is formed. So for the ORM to work relations in the DB can only form an acyclic graph. That’s bad.

Fix #3

Even though PageModel depends on CommentModel, don’t import it. Just duplicate the CommentModel code into PageModel. Ugly:

import App.Models.Types
 
instance HasChildComment (Page) where
    findAllChildComment p = do
        conn <- getEnvironment >>= (return . fromJust . getDatabase )
        res <- liftIO $ HDBC.handleSqlError $ HDBC.quickQuery' conn ("SELECT _id , commenter , page_id , post FROM comment WHERE (page_id = ?) ")  [_id p]
        return $ map (\r -> Comment (HDBC.fromSql (r !! 0)) (HDBC.fromSql (r !! 1)) (HDBC.fromSql (r !! 2)) (HDBC.fromSql (r !! 3))) res

I’m Sad

Haskell is such a lovely language, but my workaround for my module import cycles is pretty hideous. Am I missing something?

Haskell (even with the GHC extensions) seems pretty stable, but the greater GHC platform seems pretty unstable. I’ve already written about how we’re [sorta] missing a vital part of the tool chain (it was broken when I tried to build it using 6.10 the other day), but in this post I’ll focus on Haskell’s libraries (especially user generated ones).

After fairly heavy usage of Haskell over the past few months, I exit 2008 thinking that, while Haskell is a wonderful language, the library situation with GHC prevents GHC from being more heavily used. Unless you’re writing completely custom software, it can be very difficult to try a piece of Haskell software. One of the reasons Rails is so successful is that it Just Installs and the tutorials are Just That Easy. OTOH, when I start to install a new package in GHC, I never quite know what will happen.

Here are some problems I’ve had with Haskell’s libraries over the past few months/years along with possible fixes for those issues:

• Hackage != Haskell Library Repository: Hackage doesn’t necessarily contain the latest and greatest versions of a library. For example, harp on Hackage is V0.2, but harp on code.haskell.org is V0.4.
  • This could most easily be fixed by automating the pulling of code from repos. Since harp is located at code.haskell.org/hsp/harp, Hackage could automatically pull code and build packages from there.
  • The Hackage team has put together a great system. It seems fair that they have T.O.S. which keeps Hackage usable and clean. Part of the TOS would be that a package maintainer: keep the package up to date in Hackage; respond to e-mails; notify the Hackage team if the maintainer is abandoning the package.
• 6.10 ‘base’ Library Reorg: the base library reorg looks good, but it changes around a lot of the … er … basic libraries of the system.
  • Not sure of a fix here. Seems like a nice reorg and if base weren’t reorged, I’d probably be bitching about the need to reorg base… Here’s to hoping we don’t go through another base reorg any time soon.
• Bit-rotted Libraries: Libraries exist in Hackage which won’t build and which will probably never build. For example, HaskellDB is an awe-inspiring library… that hasn’t built since 6.6 and just isn’t going to build any time soon. As a newbie looking for a database library, HaskellDB would be the obvious first place to look and trying to use it would produce serious frustration (it certainly did for me). It’s nice to have a historical reference to HaskellDB in Hackage, but the package shouldn’t be listed as currently usable. Maybe it’d be sufficient to default to filtering by the latest GHC version.
  • Given Don’s post, it might not be too difficult to script weekly library builds and auto-email library maintainers about their library being broken. After a few missed e-mails, the library could be shifted to another maintainer or, at worst, deprecated.
  • Gripe about git as much as you like, but GitHub has done a great job of building an environment for ‘social coding’. Using something like GitHub would make it easy to: allow those-who-want-to-work-on-a-library to do so; move a package to a new library maintainer; provide a consistent location from which Hackage could pull code. FWIW, Rails has gone this direction…

Summary

Haskell is an awesome language. I’m a big fan (as evinced by Turbinado). Working with Haskell has forced me to think about coding in a new way and has seriously improved my coding ability. However, Haskell has also proved enormously frustrating as I try to put together a project which depends on many libraries.

A great way to increase the visibility and usage of Haskell is to make it easy to develop and build complex software in Haskell. Naturally, that requires a robust set of user libraries and that seems to require Hackage. So let’s make 2009 the Year of Hackage.

Updates

Over on reddit, Don suggests we make “2009: the year distros start supporting the platform”. enauv replies that “[GHC is] too radical and changes too quickly for platforms to truly support it.” I tend to agree with enauv, so much so that this post was originally titled “2009: GHC 6.10 LTS?” because GHC (the overall platform) does tend to change too quickly for distros to support it effectively. Maybe GHC needs to migrate GHC to Long Term Support and move bleeding edge stuff to GHC 7.0?

This post is written by a practicioner and not by an academic. I understand that Haskell is an ‘academic’ language, but Haskell has gotten popular enough that it’s no longer ‘academic’ and that’s the greatest compliment a language could receive.

How am I going to solve the library dependency problem in Turbinado? I’m going to bundle all libraries on which Turbinado depends into Turbinado. Not a solution I like, but it’s one that works…

Updated per Ganesh’s comments.

Over here, Adolfo commented:

“Hi,I tried to do follow the example, but I couldn’t even install the packages, hsx and hs-plugins were impossible. I tried with cabal and manually, and neither of those worked . any suggestion, known issue with this packages?”

I’ve been busy adding features to Turbinado and haven’t circled back around to making sure that it’s easy to build, so I can claim a lot of the blame for the build problems.  Turns out to be really important that publicly released packages are easily buildable…

Thinking back, I have really struggled to build Turbinado… and I wrote Turbinado!  Turbinado depends on some particular bugfix-ish library releases (e.g. GSomething 0.6.1). With GHC 6.10, a bunch of libraries have broken or have changed so much that they badly break Turbinado. (I need to specify better the versions in turbinado.cabal.)

At times, I’ve considered bundling the dependencies into Turbinado so that building Turbinado would be easy, but that’s always felt like a cop-out. So I’m pleading for “cabal install”. Given Turbinado’s dependence on particular versions of libraries, I would love to able to do:

cabal install turbinado
  OR  (from /home/alson/turbinado)
cabal build

Cabal Install

Most casual users of Ruby, Python, Perl, Java, etc, know that those languages have automagic build/dependencies system (respectively, gem, eggs, CPAN, maven). The tools may be of varying quality, but many tutorials include something like “First, use GEM to install the package: gem install rails” and demonstrate just how simple it is to get a useful piece of software installed.

This is not the case in Haskell. I’d guess that no more than 5% of Haskellers know about the cabal command line tool and “cabal install”. On the other hand, I’d guess that 95% of novice Rubyers know about “gem install”. These automated build/dependency system are now critical to the success of languages. As a beginner in Ruby, I always knew that I could easily try out various libraries by using GEM to install bits of software. I’m now fairly experienced with Haskell and, partly because of that experience, I don’t believe that I can easily try out various Haskell libraries.

Niklas Broberg’s HSP is a great example of the challenge of building Haskell programs. HSP is very nicely separated into modular libraries which: makes it easy to apply pieces of HSP’s functionality to a program; makes it hard for a human (at least for me) to build any one part of HSP because each part depends on so many other parts. A build/dependency tool would make HSP much easier to build into existing programs.

The Plea

I love using Haskell and Haskell will only get better if more people are able to use it. IMO, a pre-condition to the growth of the language is a solid, easy to use build/dependency system. Cabal is that system for GHC and the cabal command line tool is a key part of that system.

Unfortunately, the cabal command line tool isn’t bundled with GHC, but … Please get it, build it, use it, report any bugs, compliment the Cabal team, etc. It’ll be a great help to the Haskell community.

darcs get http://darcs.haskell.org/cabal-install
cd cabal-install
sh bootstrap.sh

Update: Haskell Platform

Ganesh points out the Haskell Platform Proposal, so it looks as though there is a plan to incorporate the cabal command line tool. See the following:

http://www.haskell.org/haskellwiki/Haskell_Platform

http://www.haskell.org/haskellwiki/Haskell_Platform/FAQ

P.S. Anyone know if the cabal command line tool is going to make it into GHC?

Links to cabal install information:

http://hackage.haskell.org/trac/hackage/wiki/CabalInstall

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cabal-install

http://ghcmutterings.wordpress.com/2008/11/10/bootstrapping-cabal-install/

First Haskell-ish post I’ve seen on Slashdot in a while:

Cryptol, Language of Cryptography, Now Available To the Public

Maybe I’m old school, but getting through the moderation on Slashdot seems like a big deal… Congrats to the Galois team!

Updated to reflect modifications to the ORM (No “Model” suffix; fractured in Types, Functions, Relations)

These are very early days for Turbinado, so much change is going on… But here’s a quick tutorial on putting together a poor man’s page editor/manager in Turbinado.

Build Turbinado

Warning!: With 6.10′s changes in dynamic plugins, Turbinado only builds with GHC 6.8 right now. Fixing this is next up in the dev queue.

You’ll need to have the following packages installed to have a go at installation:

• GHC 6.8 (darcs)
• haskell-src-exts (darcs)
• harp (darcs)
• hslogger (git)
• encoding (darcs)
• hsx (darcs)
• hs-plugins (darcs)
• http (darcs)
• HDBC (git)
• HDBC-PostgreSQL (git)

Grab the code

git clone git://github.com/alsonkemp/turbinado.git

Build it

With all of the packages installed, wait for a new moon, stand on tip-toes, and do the following:

runghc Setup.lhs configure
runghc Setup.lhs build

Configure It

cp Config/App.hs.sample     Config/App.hs
cp Config/Routes.hs.sample Config/Routes.hs

Edit App.hs and Routes.hs to taste.

Create the Page table

CREATE TABLE page (
    title CHARACTER VARYING NOT NULL,
    content text NOT NULL,
    _id CHARACTER VARYING(255) NOT NULL PRIMARY KEY,
);

Updated: added PRIMARY KEY which is needed by the ORM generator.

Generate the ORM models

runghc scripts/GenerateModels

You should now have an interesting file or two in App/Models.  The files are organized as follows: * App/Models/Bases/Comment.hs – all base Models inherit this. * App/Models/Bases/AbcXyzType.hs – the representation of the database table abc_xyz. Don’t edit this! It’s autogenerated and your changes will get ignored on the next gen. * App/Models/Bases/AbcXyzFunctions.hs – CRUD functions on abc_xyz. Don’t edit this! It’s autogenerated and your changes will get ignored on the next gen. * App/Models/Bases/AbcXyzRelations.hs – functions on tables related to abc_xyz. Don’t edit this! It’s autogenerated and your changes will get ignored on the next gen. * App/Models/AbcXyz.hs – the user configurable area of the AbcXyz. By default this just imports the above three tables. All of your custom find, insert and update methods go here.

A big shout out to .netTiers for pointing the way on building a code-generator ORM.

Create your Layout

Just as in Rails, the Layout usually defines the majority of your sites page structure. See here for the Layout used for turbinado.org.

Create your Page controller

The controller handles the request and sets up ViewData for the View to render/display. This little Page controller has the following functions/methods/actions:

• index: list all Pages.
• show: render one Page.
• new: display a blank Page form.
• create: take the submission of the ‘new’ action.
• edit: display an existing Page in a form for editing.
• save: take the submission of the ‘edit’ action.

Full version here. Here’s a snippet:

-- 'id' is an important function name in Haskell, so I use id' for the Page's "id".  There's got
-- to be a better solution
 
-- This is the generated ORM for the 'page' table in the database.
import qualified App.Models.Page
 
-- Index lists out all of the pages
-- setViewDataValue is used to store data for retrieval by the View.  Idea lifted from ASP.NET 
-- http://msdn.microsoft.com/en-us/magazine/cc337884.aspx
index :: Controller ()
index  = do pages <- App.Models.Page.findAll --use ORM goodness to get all pages
            setViewDataValue "pages-list" $ map (\p -> (title p, _id p)) pages
 
-- Show shows one page
-- Notes:
--  * The "id" is parsed from the request's path and put into the Settings.
--     See: http://github.com/alsonkemp/turbinado-website/tree/master/Config/Routes.hs
--  * getSetting returns a "Maybe a".  getSetting_u is the unsafe version and returns just the "a".
show :: Controller ()
show  = do id'  <- getSetting_u "id"
           p <- App.Models.Page.find id'
           setViewDataValue "page-title" (title p)
           setViewDataValue "page-content" (content p)
 
-- snip --
 
save :: Controller ()
save = do   id'  <- getSetting_u "id"
            _title   <- getParam_u "title"
            _content <- getParam_u "content"
            p <- App.Models.Page.find id'
            App.Models.Page.update p {title = _title, content = _content}
            redirectTo $ "/Page/Show/" ++ id'

Create Your Views

This Controller requires 4 views:

• Index
• Show
• New
• Edit – this could probably be the same as New.

See here for pre-built views. Here’s the “Index” view (note: *this isn’t very sugary and that makes me sad *):

page =  <div>
          <h1>
            Page Index
          </h1>
          <% do ls <- getViewDataValue_u "pages-list" :: View [(String, String)]
                mapM indexItem ls
          %>
        </div>
 
-- fugly, but I'm still getting used to HSP-like templating
indexItem (t,i) = return $ cdata $ unlines $
                   ["<div style='padding: 0pt 5px;'>"
                   ," <a href=\"/Page/Show/" ++ i ++"\">"
                   ,"  "++ t
                   ," </a>"
                   ,"</div>"
                   ]

Here’s the “Show” view and it’s pretty sugary:

page = <div>
          <h1><% getViewDataValue_u "page-title" :: View String %></h1>
          <% getViewDataValue_u "page-content" :: View String %>
        </div>

Run It

Start up Turbinado:

dist/build/turbinado/turbinado -p 1111

Browse to it: http://localhost:1111/Page/Index (it’ll take a couple of seconds to compile the Model, Controller and View)

Examples!

There’s still lots of work to do on the ORM and on Documentation. As the code base matures, both should progress. Examples are a nice way to drive development forward and to engage the community, so let me know if you’d like to see anything in particular demonstrated and I’ll try to implement it.

For those of you interested in Turbinado, here’s a quick status update:

• I separated the code for the turbinado.org website from the code for the framework.  The framework is here and the website code is here.
• I’m going to finish up implementing HAML templating for Turbinado in the next few days.
• After HAML templates are in, I’ll provide a tutorial on implementing a mini-CMS/wiki in Turbinado (the code is already in the website.  The standard-Rails-ish “look, Mom!  No code!” type of tutorial.  Just enough to convince you to download it, but not enough to get you to be significantly productive. 
• Adam Stark is providing some greatly needed polish here as he attempts to get this beastie to build.  Turbinado really needs to be easier to build…
• Diego Echeverri is doing some work to get Turbinado to work with GHC 6.10 here. I had a difficult time getting my HSP-ish View templates working with 6.10, so I hope Diego can do it. I’d greatly prefer to be working with 6.10, but I couldn’t get there…

Writing a little web framework turns out to be a lot of work (it’s all the little stuff (documentation!!) that really gets ya).  I’ve greatly appreciated the ability to build on the work of others (especially Niklas Broberg, Don Stewart, Bjorn Bringert and John Goerzen) and am grateful that others are providing help to this fledgling project.