gistfile1.txt

iex> use PipeInspect
nil

iex> "hello" |> String.reverse |> String.upcase |> String.downcase
"olleh"
"OLLEH"
"olleh"

pipeinspect.ex

defmodule PipeInspect do
  defmacro __using__(_) do
    quote do
      import Kernel, except: [{:|>, 2}]
      import unquote(__MODULE__), only: [{:|>, 2}]
    end
  end

  defmacro x |> f do
    inspect = quote do: IO.inspect
    stages = Enum.intersperse(Macro.unpipe(f), inspect)

    # uncomment this line to also inspect the final value
    # stages = stages ++ [inspect]

    quote do
      unquote(x) |> unquote(rebuild_pipe(stages))
    end
  end

  defp rebuild_pipe([h]) do
    h
  end

  defp rebuild_pipe([h|t]) do
    {:|>, [], [h, rebuild_pipe(t)]}
  end
end