title: What are free monads?
body: <p>I've seen the term <em>Free Monad</em> pop up <a href="http://www.haskellforall.com/2012/07/purify-code-using-free-monads.html">every</a> <a href="http://www.haskell.org/haskellwiki/Free_monad">now</a> <a href="http://www.haskell.org/pipermail/haskell-cafe/2010-January/072454.html">and</a> <a href="http://comonad.com/reader/2011/free-monads-for-less/">then</a> for some time, but everyone just seems to use/discuss them without giving an explanation of what they are. So: what are free monads? (I'd say I'm familiar with monads and the Haskell basics, but have only a very rough knowledge of category theory.)</p>