Let me preface this with acknowledging that you're entirely correct that you don't really need flatMap. The following is just some background that might explain

Let me preface this with acknowledging that you're entirely correct that you don't really need flatMap. The following is just some background that might explain why it was included. If you're familiar with C#'s linq and it's reliance on SelectMany it's somewhat easier to see the significance. In C#'s linq you might write something like: from host in sources from value in fetch_data_from(host) select create_record(value, host) with flatmap (and some abuse of notation) you can more easily implement this as: sources.flatmap( host => fetch_data_from(host) .flatmap( value => create_record(value, host)) If you dig even further you'll find that what makes this powerful is that the flatMap, together with the function x => [x], turns arrays into a Monad. The separate functions map and flat also work, but this adds more conditions. Haskell folks tend to prefer flatMap because most of the conditions for a Monad can be encoded in its type signature (except [x].flatMap(x => x) == x, but that one is easy enough to check).