Last autumn I discovered Crafting Interpreters, a book by Bob Nystrom that gives readers a comprehensive guide to writing interpreters for a toy programming language, Lox. To me the world of compilers and interpreters has always been a total mystery. Okay, so I know what a syntax tree is, and I've occassionally even been brave enough to look at the assembly output for a program I've written. Also doesn't parsing need to happen at some point? Anyway, I was pretty intrigued, so in I dived.

Bob's book is divided into two parts. The first details how to write a tree-walking interpreter in Java. Code is parsed and a syntax tree is generated from it, which is then evaluated in-place. By his own admission, this isn't a particularly efficient way to evaluate code, so the second part of the book describes how to write a stack-based virtual machine in C, which … Read more