Programming Elixir ≥ 1.6

Heads and Tails

Earlier we said a list may either be empty or consist of a head and a tail. The head contains a value and the tail is itself a list. This is a recursive definition.

We’ll represent the empty list like this: [ ].

Let’s imagine we could represent the split between the head and the tail using a pipe character: |. The single-element list we normally write as [ 3 ] can be written as the value 3 joined to the empty list:

[ 3 | [ ] ]

(I’ve highlighted the inner list.)

When we see the pipe character, we say that what’s on the left is the head of a list and what’s on the right is the tail.

Let’s look at the list [2, 3]. The head is 2, and the tail is the single-element list containing 3. And we know what that list looks like—it is our ...