In this book we will create a programming language together. We'll start with 0 lines of code and end up with a fully working interpreter for the Monkey* programming language. Step by step. From tokens to output. All code shown and included. Fully tested. Buy this book to learn: How to build an interpreter for a C-like programming language from scratch What a lexer, a parser and an Abstract Syntax Tree (AST) are and how to build your own What closures are and how and why they work What the Pratt parsing technique and a recursive descent parser is What others talk about when they talk about built-in data structures What REPL stands for and how to build one Why this book? This is the book I wanted to have a year ago. This is the book I couldn't find. I wrote this book for you and me. So why should you buy it? What's different about it, compared to other interpreter or compiler literature? Working code is the focus. Code is not just found in the appendix. Code is the main focus of this book. It's small! It has around 200 pages of which a great deal are readable, syntax-highlighted, working code. The code presented in the book is easy to understand, easy to extend, easy to maintain. No 3rd party libraries! You're not left wondering: "But how does tool X do that?" We won't use a tool X. We only use the Go standard library and write everything ourselves. Tests! The interpreter we build in the book is fully tested! Sometimes in TDD style, sometimes with the tests written after. You can easily run the tests to experiment with the interpreter and make changes. Why this book? This book is for you if you... learn by building, love to look under the hood love programming and to program for the sake of learning and joy! are interested in how your favorite, interpreted programming language works never took a compiler course in college want to get started with interpreters or compilers… ... but don't want to work through a theory-heavy, 800 pages, 4 pounds compiler book as a beginner kept screaming "show me the code!" when reading about interpreters and compilers always wanted to say: "Holy shit, I built a programming language!"