[web-devel] Rich Internet Applications using Haskell
spam at scientician.net
Thu Feb 10 08:12:59 CET 2011
I just though I'd let y'all know that I've started work on "Dingo", a
small framework for creating Rich Internet Applications (RIA) in
Haskell. The basic idea is that you write Haskell code and the framework
generates all the browser-related bits you need (HTML, JS, state
serialization, etc.) at runtime.
Writing an application is centered around Widgets and Events which are
just what you'd expect if you were writing a Gtk+/Swing/SWT/Qt
application. The way the application starts is that you provide a "start
the application" callback to a "runServer" function. When a client
connects to the server the first time, the "main" callback gets run and
can set up the main application widget however it wants.
There's a basic example in Main (see attachment). It doesn't really do
much interesting, but it does demonstrate that state transfer and
updates (client->server and server->client) work and that events work at
a basic level.
I've attached a tarball of my not-even-close-to-pre-alpha code -- I
won't bother putting this on Hackage since it's not actually useful for
any real work yet. To get something working in a browser ASAP I've taken
some... uhm, liberties with code quality, so I will not be held
responsible for self-induced eye-gouging as a result of looking at the code.
The current status is basically:
* Uses Happstack-server for serving HTTP. Given Dingo's extremely
simple serving needs it may be a bit of a "heavy" dependency, but it
works for now and it's not really a high priority to change this. It's
also definitely NOT eye-gouging-inducing, so that's a plus :).
* Only very simple widgets are included: A "panel" container widget
(corresponds to an unstyled <div/> currently) and "input", "select" and
"button" elements (corresponding to their HTML counterparts). The idea
is that Panel will be expanded to a more general container which can lay
out subwidgets horizontally or vertically.
* ALL mutable widget state is transferred to/from the browser for
every callback. This isn't an issue with the simple example in Main.hs,
but it might become an issue for larger widget hierarchies.
* Only ONE client supported at a time. You read that right. Weird
things will happen if you try to connect multiple clients.
* Find a better way to handle state transfer to lessen the burden of
having to write JSON <-> JS and JSON <-> server-state translations by
hand. I'm thinking that some of the ideas from the "Invertible Syntax"
) may apply for this. Text.JSON.Generic may also be workable, but I had
some trouble getting it to work with Text values and it doesn't help
than string concatenation. Unfortunately, HJScript seems to be *too*
strict about typing.
* Expand the selection of widgets with more complex widgets so that
I can get a feel for how the current Widget type class may need to be
generalized/tweaked. Something requiring CSS would be good too, so I can
hopefully get a basic theming mechanism down.
* Get rid of the "one client only" limitation so that Dingo may
actually become somewhat useful in practice.
* A way of tracking client-side and server-side updates so that only
things that have actually changed are transferred between client and
server. For the server side this should be easy enough and for the
client I'm thinking of something like attaching a "change()" event
handler to all relevant DOM elements.
Comments and suggestions appreciated.
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