Sorry for being not clear - was a long evening yesterday 
The mix file has a dependency {:calendar, â~> 0.16.0â}
Starting in the directory where the file resides: iex -S mix. This will load all dependencies.
As @sztosz rightly says this is the library https://github.com/lau/calendar which has more features than the built-in one in 1.3. Also, version 0.16.0 only works with Elixir 1.3, because it accepts the built-in calendar 1.3 types.
