This is the sequel to Writing An Interpreter In Go We re picking up right where we left off and write a compiler and a virtual machine for Monkey Runnable and tested code front and center, built from the ground up, step by step just like before But this time, we re going to define bytecode, compile Monkey and execute it in our very own virtual machine It s the next step in Monkey s evolution It s the sequel to a programming language Writing A Compiler In Go is the sequel to Writing An Interpreter In Go It starts right where the first one stopped, with a fully working, fully tested Monkey interpreter in hand, connecting both books seamlessly, ready to build a compiler and a virtual machine for Monkey In this book, we use the codebase included in the book from the first part and extend it We take the lexer, the parser, the AST, the REPL and the object system and use them to build a new, faster implementation of Monkey, right next to the tree walking evaluator we built in the first book The approach is unchanged, too Working, tested code is the focus, we build everything from scratch, do baby steps, write tests firsts, use no rd party libraries and see and understand how all the pieces fit together It s a continuation in prose and in code Do you need to read the first part before this one If you re okay with treating the code from the first book as black box, then no But that s not what these books are about they re about opening up black boxes, looking inside and shining a light You ll have the best understanding of where we re going in this book, if you know where we started Learn how to write a compiler and a virtual machine Our main goal in in this book is to evolve Monkey We change its architecture and turn it into a bytecode compiler and virtual machine We ll take the lexer, the parser, the AST and the object system we wrote in the first book and use them to build our own Monkey compiler and virtual machine from scratch We ll build them side by side so that we ll always have a running system we can steadily evolve What we end up with is not only much closer to the programming languages we use every day, giving us a better understanding of how they work, but also x faster And that s without explicitly aiming for performance Here s what we ll do We define our own bytecode instructions, specifying their operands and their encoding Along the way, we also build a mini disassembler for them We write a compiler that takes in a Monkey AST and turns it into bytecode by emitting instructions At the same time we build a stack based virtual machine that executes the bytecode in its main loop We ll learn a lot about computers, how they work, what machine code and opcodes are, what the stack is and how to work with stack pointers and frame pointers, what it means to define a calling convention, and muchWe also build a symbol table and a constant pool do stack arithmetic generate jump instructions build frames into our VM to execute functions with local bindings and arguments add built in functions to the VM get real closures working in the virtual machine and learn why closure compilation is so tricky