I think the piece is meant to be tongue-in-cheek like saying "A monad in is simply a monoid in the category of endofunctors." There's an essay by Peter Naur (t

I think the piece is meant to be tongue-in-cheek like saying "A monad in is simply a monoid in the category of endofunctors." There's an essay by Peter Naur (the N in BNF) called Programming As Theory Building that I think captures the author's point: http://pages.cs.wisc.edu/~remzi/Naur.pdf http://pages.cs.wisc.edu/~remzi/Naur.pdf