This was my first reaction too. Now I work in a (Swift) codebase where I could probably count the number of for loops we have on one hand. Pretty much everything is done through map/reduce/filter, etc.

At first, I thought it wasn't as readable, but now that I'm used to the syntax, I think it's much easier to parse what happening. I know what transformation is happening, and I know there shouldn't be any side-effects.