Book Image

F# 4.0 Design Patterns

By : Gene Belitski
Book Image

F# 4.0 Design Patterns

By: Gene Belitski

Overview of this book

Following design patterns is a well-known approach to writing better programs that captures and reuses high-level abstractions that are common in many applications. This book will encourage you to develop an idiomatic F# coding skillset by fully embracing the functional-first F# paradigm. It will also help you harness this powerful instrument to write succinct, bug-free, and cross-platform code. F# 4.0 Design Patterns will start off by helping you develop a functional way of thinking. We will show you how beneficial the functional-first paradigm is and how to use it to get the optimum results. The book will help you acquire the practical knowledge of the main functional design patterns, the relationship of which with the traditional Gang of Four set is not straightforward. We will take you through pattern matching, immutable data types, and sequences in F#. We will also uncover advanced functional patterns, look at polymorphic functions, typical data crunching techniques, adjusting code through augmentation, and generalization. Lastly, we will take a look at the advanced techniques to equip you with everything you need to write flawless code.
Table of Contents (20 chapters)
F# 4.0 Design Patterns
Credits
About the Author
Acknowledgements
About the Reviewer
www.PacktPub.com
Preface

Guards


At this point, I believe you would agree that pattern matching is a powerful data transformation feature. Just to further amplify the facilities considered so far, F# offers enhancing pattern-expressions with additional matching logic. Guard is represented by an arbitrary boolean expression that is attached to pattern-expression using the when keyword. The guard kicks in only if its pattern-expression host has matched. Then, the guard expression is computed, and if true, it springs the transformation performed by the corresponding result-expression to the right. Otherwise, the entire rule is considered non matched, and the matching continues in an usual manner. The when guards can be mixed and matched within a match construction in a completely arbitrary manner.

To demonstrate when guards in action, let me slightly modify the previous example. In the case where both keys are not empty, there are two subcases: when the keys are equal to each other and when they are not. Furthermore...