The web page mentions a "Haskell Symposium 2015 paper". I didn't see it linked from the page, but I'm fairly certain it's this one:<p><i>Freer Monads, More Extensible Effects</i><p><a href="http://okmij.org/ftp/Haskell/extensible/more.pdf" rel="nofollow">http://okmij.org/ftp/Haskell/extensible/more.pdf</a>