Enumerables & streams

One protocol, many collections Three deep dives

A great deal of Elixir is walking collections: a list of lessons, a map of scores, a learner's history. Anything that can be walked one element at a time implements the Enumerable protocol, and the Enum module is the toolkit for all of them. Stream is its lazy twin — the same operations, deferred until something asks for a result.

In F3.03 you piped a learner's progress through a few Enum calls. This module takes that further: the functions that summarise a collection, the for comprehension, and lazy streams that run over a full history without building every intermediate list.

When the work happens

Enum · eager — 6 + 6 + 6 elements touched
Every step builds a full intermediate list, even though two results are wanted.

One protocol, many collections

Lists, ranges, maps, MapSets, and streams are different data structures, but Enum treats them identically because each implements the same protocol. The same call works on any of them. Choose a source and watch the result hold steady.

Enum.map over a source · select one

The protocol is the abstraction: write against Enum once, and it runs on whatever collection you hand it. Maps are enumerable too — they yield {key, value} pairs, so the function takes a pair.