Programming Elixir ≥ 1.6

Reducing a List to a Single Value

The map/2 function we just wrote abstracts the idea of applying a function to each element of a list independently.

But what if we want to apply that function across the elements? How could we create an abstraction that would let us sum a list, or find the product of its elements, or find the largest element?

The sum function reduces a collection to a single value. Other functions need to do something similar—return the greatest/least value, the product of the elements, a string containing a concatenation of elements, and so on. How can we write a general-purpose function that reduces a collection to a value?

We know it has to take a collection. We also know we need to pass in some initial value (just like ...