Since the early days, Elixir has allowed us to easily process collections using the Enum and Stream modules. In the first case, the collection is traversed as soon as it reaches an Enum call, if we use the respective Stream function instead, we can delay the actual enumeration of the collection until the very last moment. This is why we say Stream functions are lazy and Enum functions are eager.
As a result, if we transform a collection by chaining Enum.map/2 calls, an intermediate collection will be created for each call to an Enum function. This behavior contrasts with the behavior we would get if we chained a bunch of Stream.map/2 calls. In the latter case, the entire collection would be traversed at most once, and only when the resulting stream reaches an Enum function (such as Enum.to_list/1), forcing each element of the stream to be evaluated.
The Enum and Stream...
