Update: HAppS 0.8.2 is out, which works with the latest version of FPS. (FPS 0.8 from latest darcs)
HAppS is an application server for Haskell. An initial read of the documentation makes it seem like a very good platform for building web applications.
The inspiration for HAppS has come from frameworks such as Python’s twisted, but with the type safety and speed that Haskell can offer. Initial performance benchmarks look quite promising.
To actually evaluate HAppS, it first needs to be installed. Below is the list of packages that go together to get it running on Mac OS X Tiger.
Versions
- HAppS (from darcs 2006-08-20) - Haskell App Server
- FPS 0.5 - Fast Packed String library
- GHC 6.4.1 for Mac OS X - Haskell compiler
- Haddock 0.7 - Documentation generator
- Happy 1.15 - Parser generator system
- HaXml 1.13.1 - XML library
- Alex 2.0.1 - Lexical analyser generator
- cpphs 1.2 - Haskell preprocessor
For Haddock to work you will also need a LaTeX system and the DocBook XSL stylesheets.
Building
GHC installs as a binary package. The remainder of the packages are installed using a reasonably standard configure; build; install process.
Haskell has its own build system, based around Cabal files that list dependencies. Most source packages will include a Setup.hs file and a *.Cabal file.
To invoke the Setup.hs file, use either the runhaskell script or make
the Setup.hs file executable (it will then hunt for runhaskell). You
need to have /usr/local/bin in your path.
$ runhaskell ./Setup.hs configure
$ runhaskell ./Setup.hs build
$ sudo runhaskell ./Setup.hs install
FPS
The Fast Packed String library allows for fast string manipulation from within Haskell. However, there is a bit of a version problem with HAppS.
- HAppS 0.8 - needs FPS 0.4 (or earlier)
- HAppS dev - needs FPS 0.5 (0.7 breaks)
FPS changes its interface between minor versions, thus breaking dependencies for HAppS. It would be good for the HAppS installation to include the list of versions used to build against, or for FPS to use better versioning.
Examples
The example that looks most interesting is httpd.hs. Based on the behavior of http://happs.org/ it appears that they are running this example as base of the site.
In the examples directory, change the import statement for the
httpd.hs file as follows:
import Data.ByteString.Char8
--import Data.FastPackedString
Assuming that you are using FPS 0.5 and the development version of HAppS.
The example can then be run from examples/ as follows:
$ make
$ mkdir HAppS
$ echo '<h1>Hello World</h1>' > HAppS/README.html
$ ./httpd
Then point Safari to http://localhost:5000/. The example will redirect to the file created above and serve the page.