Functional Programming in Go: Apply functional techniques in Golang to improve the testability, readability, and security of your code

 Cover....1 Preface....14 Title Page....2 Copyright....3 Dedication....4 Contributors....5 Table of Contents....8 Part 1: Functional Programming Paradigm Essentials....20 Chapter 1: Introducing Functional Programming....22 What is functional programming?....22 Introducing first-class functions....23 What are pure functions?....24 Say what you want, not how you want it    ....26 A brief history of functional programming....28 Modern functional programming....30 The Go programming paradigm....31 Why functional programming?....32 Why not functional programming in Go?....33 Comparing FP and OOP....34 Summary....35 Chapter 2: Treating Functions as First-Class Citizens....36 Benefits of first-class functions....36 Defining types for functions....37 Type aliases for primitives....37 Type aliases for functions....40 Using functions as objects....42 Passing functions to functions....42 In-line function definitions....43 Anonymous functions....43 Returning functions from functions....44 Functions in var....45 Functions inside data structures....46 Functions inside structs....47 Example 1 – map dispatcher....49 Creating a simple calculator....49 Example 2 – mocking functions for testing....51 Summary....55 Chapter 3: Higher-Order Functions....56 Technical requirements....57 An introduction to higher-order functions....57 Closures and variable scoping....57 Variable scoping in Go....58 Capturing variable context in functions (closures)....61 Partial application....63 Function currying, or how to reduce n-ary functions to unary functions....67 Example: function currying....69 Example: server constructor....70 Summary....74 Chapter 4: Writing Testable Code with Pure Functions....76 Technical requirements....76 What is purity?....77 Demonstrating pure versus impure function calls....77 Referential transparency....78 Idempotence....80 Statelessness....80 Side effects....80 Why does purity improve our code?....80 Increases the testability of our code....81 Increases the confidence in our code....83 Improved confidence in function names and signatures....84 Safer concurrency....85 When not to write pure functions....86 Input/output operations....86 Non-determinism can be desired....87 When we really have to panic!....87 How do we create pure functions?....87 Avoid global state....87 Separate pure and impure functionality....88 Example 1 – hotdog shop....90 Bad hotdog shop....90 Better hotdog shop....92 Summary....97 Chapter 5: Immutability....98 Technical requirements....98 What is immutability?....99 Immutability at the data layer....99 How to write immutable code in Go....100 Writing immutable code for collection data types....103 Measuring performance in mutable and immutable code....104 Benchmarking functions....104 Understanding stacks, heaps, and garbage collection....106 When to write mutable functions....109 What are functors and monads?....110 What’s a functor?....110 From functor to monad....112 Summary....115 Part 2: Using Functional Programming Techniques....116 Chapter 6: Three Common Categories of Functions....118 Technical requirements....118 Predicate-based functions....119 Implementing a Filter function....119 Any or all....123 Implementing DropWhile and TakeWhile....124 Map/transformation functions....126 Transformations while maintaining the data type....127 Data reducing functions....130 Example – working with airport data....134 Summary....137 Chapter 7: Recursion....138 Technical requirements....138 What is recursion?....139 Why do functional languages favor recursion?....141 When to use recursive functions....141 Iterating over trees....143 Recursion and functions as first-class citizens....146 Limits of recursive functions....151 Measuring the performance of recursive versus iterative solutions....151 Space limitation of recursive functions....153 Tail recursion as a solution to stack limitations....155 Summary....157 Chapter 8: Readable Function Composition with Fluent Programming....158 Technical requirements....158 Chaining functions through dot notation....159 Chaining methods for object creation (builder pattern)....159 Dot notation to chain functions on slices....161 Infinite data structures and lazy evaluation....170 Continuation-passing style programming....171 CPS and goroutines....177 When to use CPS?....178 Summary....178 Part 3: Design Patterns and Functional Programming Libraries....180 Chapter 9: Functional Design Patterns....182 Technical requirements....182 Classical design patterns in a functional paradigm....182 The strategy pattern....183 The decorator pattern....191 The Hollywood principle....195 Functional design patterns....197 Summary....199 Chapter 10: Concurrency and Functional Programming....200 Technical requirements....200 Functional programming and concurrency....201 Concurrency, parallelism, and distributed computing....201 Functional programming and concurrency....203 Creating concurrent functions....207 Concurrent filter implementation....207 Concurrent Map and FMap implementation....210 The pipeline pattern....214 Summary....222 Chapter 11: Functional Programming Libraries....224 Technical requirements....224 Is the library alive – and do the examples still match it?....225 Legal requirements....225 Pre-generics libraries for creating common FP functions....226 Code generation libraries for pre-generics Go....226 Post-generics functional programming libraries....232 Pie with generics....232 Lodash, for Go....234 Mo, for go....236 Summary....237 Index....238 About Packt....244 Other Books You May Enjoy....245