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More Complex List Patterns

More Complex List Patterns

Understand lists by implementing different kinds of operations in different cases.

The join operator |

Not every list problem can be easily solved by processing one element at a time. Fortunately, the join operator, |, supports multiple values to its left. Thus, we can write the following:

iex> [ 1, 2, 3 | [ 4, 5, 6 ]] 
[1, 2, 3, 4, 5, 6]

The same thing works in patterns, so we can match multiple individual elements as the head. For example, the following program swaps pairs of values in a list.

Run the Swapper.swap([1,2]) command in the terminal below.

defmodule First.MixProject do
  use Mix.Project

  def project do
    [
      app: :first,
      version: "0.1.0",
      elixir: "~> 1.12",
      start_permanent: Mix.env() == :prod,
      deps: deps()
    ]
  end

  # Run "mix help compile.app" to learn about applications.
  def application do
    [
      extra_applications: [:logger]
    ]
  end

  # Run "mix help deps" to learn about dependencies.
  defp deps do
    [
      # {:dep_from_hexpm, "~> 0.3.0"},
      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
    ]
  end

  def hello do
    [
    IO.puts("Hello")
    ]
  end
end
List example in Elixir

The third definition of swap (at line 6) matches a list with a single element. This definition will execute if we get to the end of the recursion and have only one ...