Expand pipelines on right-hand side of |>, closes #12070

Author: josevalim

lib/elixir/lib/kernel.ex

@@ -4115,7 +4115,11 @@ defmodule Kernel do
 
   """
   defmacro left |> right do
-    Macro.pipe(left, right, 0)
+    fun = fn {x, pos}, acc ->
+      Macro.pipe(acc, x, pos)
+    end
+
+    :lists.foldl(fun, left, Macro.unpipe(right))
   end
 
   @doc """

lib/elixir/test/elixir/kernel_test.exs

@@ -1233,6 +1233,10 @@ defmodule KernelTest do
       assert [1] |> (&hd(&1)).() == 1
     end
 
+    test "reverse associativity" do
+      assert [1, [2], 3] |> (List.flatten() |> Enum.map(&(&1 * 2))) == [2, 4, 6]
+    end
+
     defp twice(a), do: a * 2
 
     defp local(list) do