Book Image

Learning Functional Programming in Go

By : Lex Sheehan
Book Image

Learning Functional Programming in Go

By: Lex Sheehan

Overview of this book

Lex Sheehan begins slowly, using easy-to-understand illustrations and working Go code to teach core functional programming (FP) principles such as referential transparency, laziness, recursion, currying, and chaining continuations. This book is a tutorial for programmers looking to learn FP and apply it to write better code. Lex guides readers from basic techniques to advanced topics in a logical, concise, and clear progression. The book is divided into four modules. The first module explains the functional style of programming: pure functional programming, manipulating collections, and using higher-order functions. In the second module, you will learn design patterns that you can use to build FP-style applications. In the next module, you will learn FP techniques that you can use to improve your API signatures, increase performance, and build better cloud-native applications. The last module covers Category Theory, Functors, Monoids, Monads, Type classes and Generics. By the end of the book, you will be adept at building applications the FP way.
Table of Contents (21 chapters)
Title Page
Credits
About the Author
Acknowledgments
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface
Index

Domains, codomains, and morphisms


If we look closely, we can find ordered pairs of data all around us. Let's look at some statistics of Lionel Messi. The following table shows how many goals Messi scored for 10 consecutive years:

We say that the domain is set A:{2007, 2007, 2007, 2010, 2011, 2012, 2013, 2014, 2015, 2016} and the range (or codomain) is set B:{5, 6, 7, 8, 10} and that the ordered pairs are {(2007,10), (2008, 6), (2008, 8), (2010, 5), (2011, 8), (2012, 5), (2013, 5), (2014, 7), (2015, 6), (2016, 10)}.

Each year maps to a number of goals scored.

If the year where x and y was calculated by calling a function named f, we could get y by calling f(x). For example, f(2010) = 5 and f(2016) = 10.

Does the following relation make sense?

How can Messi score exactly 6 goals and exactly 7 goals and exactly 10 goals in the same year? That makes no sense, right? (Right!)

We can say that the relation of {(2007, 6), (2007, 7), (2007, 10)} which is defined by our arrows is not a function because...