RE: [Caml-list] Web Development with OCaml

[Gerd Stolpmann <info@gerd-stolpmann.de>]

On Wed, 11 Jul 2001, Francois Rouaix wrote:
>Also, I had doubts about the usefulness of a mod_ocaml. In practice (meaning
>in the real .com world, where I was working at the time), one uses multiple
>tier architectures. And you want something in the frontend that is simple
>enough
>that non-real programmers can still tweak; something that only does layout,
>and
>no logic.

A good comment. I am currently doing web development, and from my experience the
separation of layout and logic is very useful for real-world projects. Not only
because non-programmers can contribute, but also because of general
maintainability (customers often want only layout changes).

200 requests per second for a web application? Well, I must admit that my web
apps are much slower, maybe you can get 5 rps on a single CPU. But my
applications are very complex, and a clean design was more important than
speed. So I think a high-speed web platform isn't what I need.

My apps are always mixtures of languages and principles. Most of them use Perl
scripts to describe the front-logic, O'Caml as powerful background engine, and
XML to describe the layout. Many applications are simply CGIs. If speed did not
suffice, I switched to a simple application server architecture: A CGI program
is the connection between the web server and the application server, and the
latter simply forks for every new request. This works fine, is rock-stable, and
is fast enough (~0.5 seconds request/response time).

I already mentioned earlier this year on this list that I have written an
XML-based template system that makes it easy to separate layout and logic.
Sorry, I have not found the time to release it. I hope I can do it in the next
weeks (my boss is in holidays).

I have further plans with PXP, my XML parser. The idea is to have a camlp4
syntax extension for embedded XML. You can simply write something like

let table_row (a,b) =
  <:xml< <tr><td>This is $a</td><td>And this is $b</td></tr> >>

let table rows =
  <:xml< <table><?list rows?></table> >>

let my_tab =
  table (List.map table_row ["the first row","another cell"; 
                             "the second row", "nonsense"])

(I am not sure about the syntax.)

A converter from XML to HTML is very simple to write, such that a web app could
dynamically create the XML tree in memory, optionally validate it, and write it
as HTML code. I think that would already simplify web development a lot.

For a complex web application, one needs more library modules. For example a
module that manages the "micro-state" of the application (i.e. the state that
is not stored by the database but simply passed through all requests).
Furthermore modules that help to create and manage HTML widgets.

Gerd
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