Either the author has a shiny new keyboard with a λ key, or they really really like to copy and paste.

Syntax error: Either data constructor not in scope.

Perhaps you meant one of these:

   Left "the author has a shiny new keyboard with a λ key"

   Right "they really really like to copy and paste"

Shiny new keyboard: http://bepo.fr/

Or a programmable text editor. I bind λ to S-l in emacs.

As far as I know, it isn't. I just figured that anyone who understand '\' might understand 'λ' as well. And those who don't know Haskell might just figure that 'λ' stands for 'function'.

Lisp and Ruby, among other languages, actually use the word 'lambda' as a keyword for declaring an anonymous function. It's more typing than "\", but the intent is clear.

I don't think Haskell is really the best choice of language for demonstrating these FP concepts simply because Haskell's syntax is a little cryptic to those who haven't studied it. Lisp would have been a more readable choice since the syntax is trivial.

Also, you didn't touch on recursion, which is a key concept in FP. The idea of having a function call itself repeatedly in order to loop through a data structure, instead of iterating over the data structure by mutating a counter variable, is a huge paradigm shift for people who are new to FP.

Yes. But in practice we almost never recurse through a data structure directly. We once recursively define a combinator to fold the datastructure, and then always use that combinator for working with the data structure.

But in that way your Haskell code examples seem to not be valid Haskell anymore. Seems to be a rather pointless change for the sake of simply breaking things.

Well, given this: http://news.ycombinator.com/item?id=5278883 I now believe the notation needs to be explained anyway. I'll switch back to '\'.