Can Programming Be Liberated From The Von Neumann Style? (1977) [pdf] 12 years ago
User-defined, powerful operators are the most important feature that make programming in Haskell feel so foreign. Yet, since they often require the programmer to sort of grasp a model of the thing the program is trying to accomplish, once you understand the operators (e.g. parser combinators) you have a rather deep understanding of the foundation for this particular program and the rest of the code is expressed very concisely and (sometimes) reasoned about easily.
Regarding the short variable names in math: They are supposed to be written and, more importantly, manipulated by hand and so short notation is very important.