Examples from the Book "Learn You A Haskell For Great Good"

The book can be read online at learnyouahaskell.com

Lessons learned

learning how to think recursively is essential
implementing foldl and foldr by yourself is the best way to really understand them
too much function composition with . is not advisable
Functor typeclass is fundamental for many other typeclasses
Applicative is a beefed up Functor
Monad is a beefed up Applicative
learning about kinds is essential for really understanding types
when in doubt, why not use a good old list comprehension?
list comprehensions are a good fit for code challenges
guards make the code extremely readable
use generic versions of functions like length and take
if you speak a different language than English, implement types like Maybe or Either in that language, it's a great exercise (e.g. data Vielleicht a = Nichts | Einfach a, then make the according instances)

The notes on this book turned into a vague reference for Haskell and can be found at doc.robelv.net