The Elixir Pipe Operator

The Elixir pipe operator (|>) is beautiful.

How do you use it? Imagine you have a data structure and two or more functions that transform it in sequence.

Suppose you have a Numbers module in a file called numbers.ex:

defmodule Numbers do

  def filter_even_numbers(list) do
    Enum.filter(list, fn x -> rem(x, 2) == 0 end)
  end

  def double(list) do
    Enum.map(list, fn x -> x * 2 end)
  end

end

Then, open an Interactive Elixir session:

$ iex numbers.ex

Now, if you copy and paste this into your iex session:

iex> [1, 2, 3, 4, 5, 6]
|> Numbers.filter_even_numbers()
|> Numbers.double()

You’ll get:

[4, 8, 12]

Some say the pipe operator came from F#. I once asked José Valim, and he said he doesn't remember exactly where the idea came from. But it’s true that F# had pipe operators—more than one kind—before Elixir.

Want to go deeper into the pipe operator? Check out this excellent blog post by João Paulo Abreu: Learning Elixir: Pipe Operator. Don’t miss the “Further Reading” section.

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— Adolfo Neto (@adolfont.github.io) June 13, 2025 at 8:49 AM