Book Image

Learn Type-Driven Development

By : Yawar Amin, Kamon Ayeva
Book Image

Learn Type-Driven Development

By: Yawar Amin, Kamon Ayeva

Overview of this book

Type-driven development is an approach that uses a static type system to achieve results including safety and efficiency. Types are used to express relationships and other assumptions directly in the code, and these assumptions are enforced by the compiler before the code is run. Learn Type-Driven Development covers how to use these type systems to check the logical consistency of your code. This book begins with the basic idea behind type-driven development. You’ll learn about values (or terms) and how they contrast with types. As you progress through the chapters, you’ll cover how to combine types and values inside modules and build structured types out of simpler ones. You’ll then understand how to express choices or alternatives directly in the type system using variants, polymorphic variants, and generalized algebraic data types. You’ll also get to grips with sum types, build sophisticated data types from generics, and explore functions that express change in the types of values. In the concluding chapters, you’ll cover advanced techniques for code reuse, such as parametric polymorphism and subtyping. By end of this book, you will have learned how to iterate through a type-driven process of solving coding problems using static types, together with dynamic behavior, to obtain more safety and speed.
Table of Contents (12 chapters)

Starting Type-Driven Development

In this book, we are exploring the techniques and idioms available in type-driven development. Some people also refer to type-driven development as type-level programming. Static types offer several benefits, including:

  • Preventing incorrect code from getting a chance to run
  • Documenting the current codebase
  • Helping to correctly refactor the codebase by pointing out any parts of code you may have missed
  • Offering richer IDE support, for example, auto-completion
  • Better performance when the compiler knows types and can optimize code accordingly

Type-driven development is the practice of using static types to restrict what your code can do. Normally, your programming language gives you enough power to represent any computation. With type-driven development, you are essentially trying to make it impossible for your code to do undesirable things.

In this chapter, we will do some basic critical analysis of a piece of code and look at the possible errors it may contain. We'll also introduce ReasonML, the language we will use to learn type-driven development and compare it with JavaScript. We'll get started with a basic Reason project and then introduce Reason, as well as its related communities and ecosystems.

In this chapter, we will cover the following topics:

  • The main idea and benefits of type-driven development
  • Dynamically typed code versus its statically typed ReasonML equivalent
  • The Reason language, ecosystem, and related projects
  • How to set up a basic Reason project, which we will use throughout this book
  • The Try Reason online playground