You can find extensive free samples on:
The bold & italicized atoms in the Table of Contents are those included in the Leanpub free sample, so you can become comfortable with the material and ensure it’s a good fit before buying. Please install it on your reading device to verify that you don’t have any issues before purchasing.
The Stepik free sample includes beginning portions of all the non-bold & italicized atoms in the Table of Contents.
If you purchase the early-access edition you will receive updates as they become available.