Yet another little Elm experiment!
This time I wanted to visualize quad trees. By far the hardest part of this whole experience was figuring out how to draw them. The mouse positions are received with the positive y direction going downwards from the top of the screen, the Graphics.Collage routines expect x and y to be centered in the middle of the screen (with y positive going up), and I structured the trees to expect the origin to be the bottom left (y positive going up)!
You can play with it here
The code is on my github repository in the Elm directory as quad.elm