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.

Preface

Who this book is for

What this book covers

To get the most out of this book

Free Chapter

Starting Type-Driven Development

Starting Type-Driven Development

Analyzing code for hidden errors

Programming with Types and Values

Programming with Types and Values

Types and values

Static and dynamic environments

Packaging Types and Values Together

Packaging Types and Values Together

Syntactic modules

Module signatures

Type abstraction

Grouping Values Together in Types

Grouping Values Together in Types

JavaScript object types

Putting Alternative Values in Types

Putting Alternative Values in Types

The power of switch

Polymorphic variant types

Generalized algebraic data types

Designing for correctness with types

Making Types That Can Slot into Any Other Type

Making Types That Can Slot into Any Other Type

Type inference and generic types

The list – modeling more than one

The option – modeling either none or one

Mutable parameterized types – ref and array

Forcing a difference with phantom types

Making Types That Represent Operations

Making Types That Represent Operations

Function types and other useful properties

Multiple arguments and currying

Reusing Code with Many Different Types

Reusing Code with Many Different Types

Polymorphism in Reason

Generic code with functors

Extending Types with New Behavior

Extending Types with New Behavior

Subtyping using polymorphic variants

Code reuse with OOP-style inheritance

Bringing It All Together

Bringing It All Together

Starting with a variant type (version 1)

Using more pattern matching (version 2)

Switching to polymorphic variant types (version 3)

Using records (version 4)

Using modules for code structure (version 5)

An alternative code structure (version 6)

An improvement – using lists as output (version 7)

Another improvement – using mutable records (version 8)

Unit testing our code (final version)

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Making Types That Represent Operations

In previous chapters, we've seen how to build types to model many kinds of data. Through all of these chapters, we've relied on functions. Functions wrap calculations and actions for easy reuse, so it makes sense that they're among the most heavily used features in any programming language. So, by taking advantage of Reason's type system and functional programming techniques, we can design functions for maximum effectiveness.

In this chapter, we will cover the following topics:

Meaningful function types and useful properties
Currying and partial application
Higher-order functions
Using functions to control dependency ordering and program flow
Commonly used functions and operators

But first, what is a function? A function in type theory and mathematics has a formal definition, but we can think of it as a formula for calculating...