The web page mentions a &quot;Haskell Symposium 2015 paper&quot;. I didn&#x27;t see it linked from the page, but I&#x27;m fairly certain it&#x27;s this one:<p><i>Freer Monads, More Extensible Effects</i><p><a href="http:&#x2F;&#x2F;okmij.org&#x2F;ftp&#x2F;Haskell&#x2F;extensible&#x2F;more.pdf" rel="nofollow">http:&#x2F;&#x2F;okmij.org&#x2F;ftp&#x2F;Haskell&#x2F;extensible&#x2F;more.pdf</a>