What I cannot create, I do not understand.

Just because you've implemented something, doesn't mean you understand it.

Real World Haskell online for free

It’s totally awesome that this is freely available online. Haskell was a little low on my “to-learn” list but it just jumped up because I really enjoyed the introduction and I think the combination of strong typing and lazy evaluation might make a nice complement to my recent return to Scheme.

http://book.realworldhaskell.org/read/