This is an example of how to use Haskell to talk to an Open Pixel Control server, such as a FadeCandy, to control strings of RGB LED lights.

Additionally, this program listens for a button press on GPIO2, and switches between different patterns of lights each time the button is pressed.

The button should be connected between GPIO2 and GND, which are pins 13 and 14 on the Raspberry Pi's main GPIO connector.

This program uses the wiringPi C library to talk to the GPIO, so you'll need to install wiringPi before building this program. On Raspbian "Jessie", wiringPi is available as a package:

sudo apt-get install wiringpi

You'll also need to set the WIRINGPI_GPIOMEM environment variable (to any value) before running this program, so that you don't have to run it as root.

For more information, see my blog post.