<h3>Real World HAppS</h3>
$!<p>Haskell is a great way to program.</p>!$
<p><a href="http://www.happs.org">HAppS</a> is a great way to build web applications.
Besides having a great feature set in its own right, it is probably the leading solution
for implementing web apps in <a href="http://www.google.com/search?hl=en&q=why+haskell">haskell</a>,
my favorite language.
$!<p>You also get all the <a href="http://www.google.com/search?hl=en&q=why+haskell">goodness</a>
that comes from programming in <a href="http://www.haskell.org">haskell</a>, my favorite language.</p>
!$
<p>HAppS is especially great if you believe, like I do, that as
modern software systems tend toward ever increasing complexity,
database usage is an unnecessary source of complication that
<a href=http://gilesbowkett.blogspot.com/2007/05/sql-unnecessary-in-haskells-happs.html>should be factored out</a> where possible.
<p>Ruby's <a href="http://rubyonrails.com/">rails</a> and python's <a href="http://www.djangoproject.com">django</a> have become popular largely because of their <a href="">object relational mapping</a> systems,
which hide the complexity of database engines by converting application data manipulation logic into sql.
When I first used an ORM, it felt like a huge improvement over writing sql statements every time I wanted to manipulate
an application's state. But pretty soon ORMs started seeming hackish to me too. At some point,
the metaphors I wanted to use just <a href="http://en.wikipedia.org/wiki/Object-Relational_impedance_mismatch">broke down</a>.
$!Or to put it another way, that <a
href=http://gilesbowkett.blogspot.com/2007/05/sql-unnecessary-in-haskells-happs.html>sql
is an ugly hack</a>. !$
<p> HAppS is haskell's answer to rails and django (and perl's <a href="http://www.catalystframework.org/">catalyst</a>,
and <a href="http://www.php.net">php</a>).
$! , and every ORM ever written in the history of software) !$
With HAppS, there is no wrangling data
structures into and out of the database, because there is no database. You use whatever data
structures are natural to your application, and serialize them
transparently using
<a href="http://www.google.com/search?q=scrap+your+boilerplate">powerful</a>
machinery</a> that's running <a href="http://www.haskell.org/th/">behind the
scenes</a>. And if there are existing databases that you need to connect to, you can do that too
-- you're not locked in to using macid for everything.
<p><a href="http://hackage.haskell.org/packages/archive/HAppS-State/0.9.2.1/doc/html/HAppS-State.html#1">MACID</a>,
the HAppS storage mechanism, is no vanilla serialization layer that will
start acting in weird ways when an application has many concurrent users doing possibly conflicting things.
By <a href="http://research.microsoft.com/~simonpj/papers/stm/">leveraging haskell's type system</a>
(see composable memory transactions paper),
you get the same <a href="http://en.wikipedia.org/wiki/ACID">ACID</a> guarantees that
normally only come with a database. </p>
<p>There are some <a href="/tutorial/macid-stress-test">limitations</a> to using macid
as a datastore that you should familiarize yourself with
if you are looking into using HAppS for heavy-usage transactional applications.
But long term, HAppS with macid looks promising enough that I've started
using it as a platform for building commercial web 2.0 type apps. (My first
commercial happs app will be public soon, so stay tuned on
<a href=http://www.techcrunch.com>techcrunch</a>. :) )
<p>In short, HAppS is awesome, and webmonkeys everywhere should use it. Except...
<p>There is this one <a href="/tutorial/missing-happs-documentation">minor detail</a>.