This document introduces the Enum module in Elixir, which provides functions for looping and iterating over enumerables without using explicit loops. It describes common use cases for looping like transforming or aggregating elements. The Enum module uses recursion under the hood to handle each case. Key functions like Enum.map and Enum.reduce are explained, with Enum.map transforming each element and Enum.reduce collecting results into a single value. The document recommends learning the Enum module as it is very useful and provides a functional approach to looping.

1. Enum is your new best
friend
Jeffrey Chan
Alembic
Twitter: @jgmchan
Github: https://github.com/jgmchan
Email: jgmchan@gmail.com

2. A lot of tutorials
https://www.reddit.com/r/ProgrammerHumor/comments/6d3eqh/functional_programming_for_beginners/

3. Overview
What’s the Enum module
Enum.map
Enum.reduce
Other handy Enum functions

4. Common beginner question
“How do I loop?”

5. Common answer
“Oh, you don’t need loops. Just use
recursion”

6. Common reaction to answer

7. But seriously, how do you loop?
The correct answer is actually recursion 🤪
…but the easier/more common answer is the
Enum module

8. Why do we actually loop?
Common use cases:
Doing something to/with a sequence of elements, e.g.
Change every element to something else
Count the elements
Sum all the elements
Doing something until a condition is triggered e.g.
Do something x number of times
Do something until `foo == true` or event is triggered

9. Why do we actually loop?
Common use cases:
Doing something to/with a sequence of elements, e.g.
Change every element to something else
Count the elements
Sum all the elements
Doing something until a condition is triggered e.g.
Do something x number of times
Do something until `foo == true` or event is triggered Recursion
Enum

10. Non-functional languages
output = []
for x in [1,2,3,4] do
output << x*x
end
output == [1,4,9,16]
output =
[1,2,3,4]
|> Enum.map(fn x -> x*x end)
output == [1,4,9,16]
Non-functional (pseudo) Functional (Elixir)

11. Enum module
https://hexdocs.pm/elixir/Enum.html
Provides a ton of functions to deal with the
use cases of loops
Probably the module I use the most when
programming with Elixir
Under the hood, it’s ALL recursion

12. Enum functions - Little factories
Takes an input
Takes a function to deal with a single element
Outputs the result
Input is NEVER changed (immutable data)

13. Enumerable
Input must be an Enumerable
Something that can be enumerated
e.g. Maps, Lists, Strings, …
Tuples, Structs are not enumerable
X elements

14. Enum.map
Transforms/modifies each element in the input
Size of output is the same as the input
X elements X elements
f( ) =

15. Enum.reduce
The most important function in Enum. Pretty much every other
function in Enum is built from reduce
Go through each element and collect the result
Quite complicated to wrap your head around initially but well
worth the effort - see Paul’s talk
X elements Single object/collection
f( , ) =

16. Other handy functions
Enum.filter/reject
Enum.into
Enum.sum
Enum.uniq
Enum.zip
Enum.with_index 0 1 2 3

17. Tip
Use the function that changes your input size
to the required output size
X elements X elements
X elements Single object/collection
<= X elementsX elements

18. Conclusion
Enum module is super handy and well worth
the effort to learn, most bang for buck
Think of them as inputs, f(x), output
Deep down it's all recursion (but we can let
someone else worry about that)