[chousuke]

Applicative and Monad and their operators are really something I would consider required Haskell knowledge. It's not surprising that you can't read Haskell code if you don't know what those are, because they are everywhere by virtue of being such useful abstractions.

Granted, Haskell people seem to have a sometimes unhealthy attraction towards having operators for everything. The Lens package in particular is rather awful in this regard IMO. (Fortunately there are non-operator equivalents to everything)