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

Wildcard matching


If I put the preceding scripts into Visual Studio, the F# source code editor will draw a blue warning squiggle line under the ``compare me`` comparison expression, indicating that the set of rules in this match construction is not exhaustive, as shown in the following screenshot:

An example of an incomplete pattern matching

The compiler even gives a sample value of ``compare me``, which is not going to match. Although this value is not present within the definition of type Multiples, if I synthetically create this value as enum<Multiples>(1) and feed it as an argument into transformB, the result would be the run-time exception of type Microsoft.FSharp.Core.MatchFailureException. This situation should raise the following question: how would it be possible to put a match all rule into the match, which means anything that was not specified in preceding rules?

For this purpose, F# offers the special wildcard pattern  _ that matches anything that was not matched in the preceding...