Using Browser as Front End

I know using browser as a front end is not a new idea but I found out
recently that WebSocket makes pushing data to browser very easy to do.

My personal interest is to use the javascript libraries supported by
browsers (D3 in my case) for visualization, while retaining control in a
Prolog console -- so I don't have to write a web server. This turns out
fairly straightforward. I know that SWI does not yet support WebSocket, but
one can write a simple man-in-the-middle server easily in anything that
supports WS. My first try was with nodejs. Then I tried with Emacs/Elisp
since I access SWI from Emacs with ediprolog. Both worked out well in my
simple use case, where it is just one way traffic from Prolog to the
browser. But as a proof of concept I see it as a good sign for more
ambitious undertakings.

My setup is like this: start servers (WS and TCP) in the host platform. I
use emacs but nodejs also works with little coding. Connect the browser to
the WS server (through embedded javascript in a local html file). Connect
Prolog to the TCP server. The host platform then simply copies any data
coming in through the TCP socket over to the outgoing WebSocket. As I said
I only implemented the half duplex part for my personal use, but servers
should be neutral on the direction of flow. I would have to set up my
Prolog client to handle async data and have not got around to it as I am
happy with running things from my ediprolog console, which runs
synchronously. Above the data layer I wrote some js client code to display
data, and I then send over data from Prolog (encoded in json with embedded
dispatching information) and have the data rendered in the browser. I also
use the same websocket to update my js client code whenever I have a need
to (like after creating a new display function). So the REPL is complete
for both js and Prolog.

My primary intention is just to share the idea and hopefully someone will
find it helpful.

On a more tentative note, Carlo Capelli  has recently ported the Prolog
console to Qt. Is there an interest in creating a javascript based frontend
for SWI? There are a lot of UI and graphics libraries available through js.
With Websocket async two way communication is easy as well.

Just a thought,

Haitao Zhang
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