Add exercises 6 and 7 from chapter 14

Author: Bernard Pietraga

chapter_14/working_with_multiple_processes_6.exs

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+# self is a function and assigned points to parent

chapter_14/working_with_multiple_processes_7.ex

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+defmodule Parallel do
+  def pmap(collection, fun) do
+    me = self()
+    collection
+    |> Enum.map(fn (elem) ->
+      spawn_link fn -> (send me, {self(), fun.(elem)}) end
+    end)
+    |> Enum.reverse
+    |> Enum.reverse
+    |> Enum.map(fn (pid) ->
+      receive do {_pid, result} -> result end
+    end)
+  end
+end
+
+ExUnit.start
+
+defmodule ParallelTest do
+  use ExUnit.Case
+
+  test "pmap returns list with proper sorted order" do
+    square_list = [
+      1, 4, 9, 16, 25, 36, 49, 64, 81,
+      100, 121, 144, 169, 196, 225, 256,
+      289, 324, 361, 400, 441, 484, 529,
+      576, 625, 676, 729, 784, 841, 900,
+      961, 1024, 1089, 1156, 1225, 1296,
+      1369, 1444, 1521, 1600, 1681, 1764,
+      1849, 1936, 2025, 2116, 2209, 2304,
+      2401, 2500
+    ]
+
+    expected = Parallel.pmap(1..50, &(&1 * &1))
+    assert expected != square_list
+  end
+end