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

Matching literals


One of the simplest cases of matching patterns is a pattern represented by a literal and assuming a simple comparison-expression value equality. Literals can be of any numeric, character, or string types. They can also be cases of a .NET enumeration (each such case is inherently a symbolic name alias of the integer value) or a value decorated with the [<Literal>] attribute.

In the following script, I can easily match int literals and the int value aliased as THREE, decorated with the [<Literal>] attribute (Ch4_1.fsx):

[<Literal>] 
let THREE = 3 
 
let transformA v = 
  match v with 
  | 1 ->"1" 
  | 2 ->"2" 
  | THREE ->"3" 
 
transformA <| (1 + 2) 

This yields string "3", as expected. However, it wouldn't be possible to mix int literals with named int constant values from the following script (Ch4_1.fsx):

type Multiples = 
  | Zero = 0 
  | Five = 5 
 
let transformB ``compare me`` = 
  match ``compare me`` with 
  | Multiples.Zero ->"0" ...