lisering/lisp-rs

This repository is a hands-on tutorial that teaches you how to build a Lisp interpreter from scratch using the Rust programming language. The tutorial is structured as 74 incremental steps with 173 tests along the way, and by the end you have a working interpreter. No prior knowledge is required and the project uses zero external dependencies, meaning everything is built from the ground up so you can see how each piece works. The README is written for beginners and spends time explaining what programming actually is before touching any code. It introduces Lisp as the second oldest programming language, born in 1958, and describes its distinguishing trait: code and data are the same thing, both expressed as lists. Lisp syntax has only two rules, according to the author. Parentheses mean "call the first item with the remaining items as arguments," and you can nest parentheses inside each other like Russian dolls. That is the entire grammar. The tutorial is organized into chapters that build on each other. Early steps cover preparation, understanding values, and splitting program text into words. Middle steps introduce naming things, doing real computation, and adding more data types. Later steps cover making programs choose between paths, remembering the past through closures, and running faster through performance optimization. The README includes a visual roadmap showing how each chapter depends on the ones before it, and it offers multiple entry points depending on your background, so someone who already knows Rust can skip ahead while a complete beginner starts from the beginning. A notable feature the README highlights is tail call optimization, demonstrated with an animation showing one million iterations running without stack overflow. The tutorial also walks through closures with what it calls a "backpack-closure trace" and a trampoline loop for optimization. The full README is longer than what was shown.