First and above all, I praise God, the almighty, for providing me with this opportunity and granting me the capability to proceed successfully. To my wife, dear Vivin, without whose support and encouragements I could not have finished this book. Thank you for reminding me of the deadline of each chapter, so I could always stay on the writing process schedule. To my beloved sons, the source of my joy: Olav, who makes my life worth living by giving me much happiness, and Oliver, who was born just after I submitted the draft of chapter 5. His first cry boosted my spirit to finish this book. And a thank you to my parents and family for their inspiration.

Also, I would like to express my gratitude to the following individuals who supported me in writing this book:

The team at Packt, especially Denim Pinto, my acquisition editor, who invited me to author this book; Priyanka Mehta, my content development editor, for her constant effort in encouraging me to supply the best content for this book; and to all reviewers who have given input and suggestions to make the content of this book much better.

My best mentor, teacher, and superior at CIPTA (www.cipta.com), Benediktus Dwi Desiyanto, who never let me stop learning new things and always encourages me to catch my dream. Hope this book can be the way to make all my dreams come true.

Chief Executive Officer of CIPTA, Steven Chandra, for providing me with a new Amazon Kindle. Since then, the number of books I have read has increased. The insight from the books I have read was helpful while I wrote this book.

Chief Human Capital Officer of CIPTA, Budi Setiawan, for appreciating my work in authoring my previous book and inviting me to join the C-MAG (CIPTA Magazine) press team. It helped me a lot in enhancing my writing skills.

All my friends and colleagues at CIPTA, especially Muhammad Abdurochman Sanjaya and Seno Budi Utomo, for the insight of C# programming in developing a smart card application. It helped me develop the application I presented in this book. And Andre Tampubolon, for the insight of functional programming in Haskell.

Dave Fancher, the author of The Book of F#, thank you for your amazing site, https://davefancher.com/, my one-stop place to learn functional programming. His website inspired my authoring of this book.