Refactor some functional compositions

functional.ex

defmodule Functional do
  def run() do
    source = """
    def f(xs, f) do
      Enum.map(xs, f) |> Enum.join(",") 
      Enum.map(xs, f) |> Enum.into(",") 
    end
    """

    ast = Code.string_to_quoted!(source)

    Macro.traverse(ast, %{issues: []}, &prewalk/2, &postwalk/2)
  end

  @pairs [{:map, :join}, {:map, :into}]

  for {f1, f2} <- @pairs do

  def prewalk(
        {:|>, [line: line],
         [
           {{:., _, [{:__aliases__, _, [:Enum]}, unquote(f1)]}, _, _},
           {{:., _, [{:__aliases__, _, [:Enum]}, unquote(f2)]}, _, _}
         ]} = ast,
        acc
      ) do
    {ast, %{acc | issues: [{line, unquote(f1), unquote(f2)}|acc.issues]}}
  end
  end

  def prewalk(ast, acc) do
    {ast, acc}
  end

  def postwalk(ast, acc) do
    {ast, acc}
  end
end