On: Functor, Applicative, and Monad

[pdpi]

Map-reduce is effectively the fruit of realising that, as long as your processing can be described as a combination of Functor (map) and Monoid (reduce) operations, then you can trivially parallelise your computation by letting the implementation of `map` and `reduce` handle all the parallelism for you.

[3PS → pdpi]

A question. Does map-reduce assume a commutative monoid, or does it need to order the output of map?

Edit: seems like it's the latter.