FWIW, I've had to write similar code when there's some complex "folding" operation. I use map/filter a lot, but fold/reduce/accumulate always seemed harder to u

FWIW, I've had to write similar code when there's some complex "folding" operation. I use map/filter a lot, but fold/reduce/accumulate always seemed harder to understand than a for loop. I also prefer nested loops rather than nested iterators.