Source code: https://github.com/moroshko/sliding-puzzle
However, that will change in a future release of Elm, once Joey Eremondi's work has been fully integrated. My understanding is that integration is not slated for the 0.16 release (imminent) but will likely be part of the 0.17 release.
See: https://groups.google.com/forum/#!searchin/elm-dev/dead$20co...