mathr / blog / #

I implemented in Haskell some symbolic algorithms related to the Mandelbrot set, but setting up a Haskell tool-chain to try it out is quite a barrier to entry. Some time ago I wrote a server-side web interface, but I didn't run it live on the web because of security concerns (mainly denial of service from heavy computations). Last week I finally got around to installing GHCJS (pro-tip: trying to install in a sandbox is more trouble than its worth), a Haskell to JavaScript compiler, and ported the web interface to run client-side in the browser, neatly side-stepping any security issues and also allowing offline usage.

You can try it out at /mandelbrot/web/, there's no documentation to speak of but hopefully the examples should be enough to get you started. Some calculations can take a long time, but GHCJS's scheduler avoids the dreaded browser "script taking too long" popup, provided the calculations are not in a synchronous callback (thanks to luite in the #ghcjs IRC channel on freenode for pointing this out).

The source code for the web interface is at mandelbrot-web which also requires my mandelbrot-symbolics and mandelbrot-text libraries. You can also download the compiled web interface as a tarball: web.tgz. It has been postprocessed with closurecompiler, as documented on the GHCJS deployment page, which reduced the size quite a bit. Pro-tip #2, Debian calls the nodejs binary "/usr/bin/nodejs", but npm packages expect just "node" - I put a little script in ~/opt/bin/node (which is in my $PATH) to make it work properly:

#!/bin/sh
exec nodejs "$@"

I plan to adapt the web interface further to include support for my mandelbrot-numerics library and eventually image rendering with annotations - though there won't be deep zoom support until I find an efficient JavaScript BigFloat library that I can FFI to, or an efficient pure Haskell BigFloat implementation (my variable-precision library is probably too slow and wasteful to be useful).