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Learn Type-Driven Development

By : Soumya Mukherjee, Amin, Kamon Ayeva

5 (1)

Buy this Book

Learn Type-Driven Development

5 (1)

By: Soumya Mukherjee, Amin, Kamon Ayeva

Buy this Book

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

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Free Chapter

Starting Type-Driven Development

Analyzing code for hidden errors

Adding types

ReasonML

Summary

Programming with Types and Values

Workflow

Types and values

Static and dynamic environments

Errors

Summary

Packaging Types and Values Together

File modules

Syntactic modules

Module signatures

Module errors

Type abstraction

Summary

Grouping Values Together in Types

Record types

Tuple types

Object types

JavaScript object types

Summary

Putting Alternative Values in Types

Variant types

The power of switch

Polymorphic variant types

Generalized algebraic data types

Designing for correctness with types

Summary

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

Summary

Making Types That Represent Operations

Function types and other useful properties

Multiple arguments and currying

Summary

Reusing Code with Many Different Types

Polymorphism in Reason

Generic code with functors

Summary

Extending Types with New Behavior

Subtyping using polymorphic variants

Code reuse with OOP-style inheritance

Summary

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)

Summary

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Workflow

To get the most from this chapter, we will set up a comfortable edit-compile workflow. We recommend placing two windows side-by-side in your editor. VSCode supports this functionality with the View | Split Editor command. On one side, load a Reason source file; on the other side, load the JavaScript output file (once it is initially compiled). Then in a terminal, run the following command:

bsb -w

The preceding command starts a build in watch mode, which automatically recompiles any parts of a project that are affected whenever you change any source code. In fact, watch mode is smart enough to also remove an outdated JavaScript output file whenever its corresponding Reason source file is deleted. The editor will also auto-reload the compiled JavaScript file whenever you save a Reason source file.

In VSCode, you can also open a terminal session directly below the files...

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