Why build a Lisp

The language we are going to be building in this book is a Lisp. This is a family of programming languages characterised by the fact that all their computation is represented by lists. This may sound scarier than it is. Lisps are actually very easy, distinctive, and powerful languages.

Mike Tyson • Your typical Lisp user

Building a Lisp is a great project for so many reasons. It puts you in the shoes of language designers, and gives you an appreciation for the whole process of programming, from language all the way down to machine. It teaches you about functional programming, and novel ways to view computation. The final product you are rewarded with provides a template for future thoughts and developments, giving you a starting ground for trying new things. It simply isn’t possible to comprehend the creativity and cleverness that goes into programming and computer science until you explore languages themselves.

The type of Lisp we’ll be building is one I’ve invented for the purposes of this book. I’ve designed it for minimalism, simplicity and clarity, and I’ve become quite fond of it along the way. I hope you come to like it too. Conceptually, syntactically, and in implementation, this Lisp has a number of differences to other major brands of Lisp. So much so that I’m sure I will be getting e-mails from Lisp programmers telling me it isn’t a Lisp because it doesn’t do/have/look-like this or that.

I’ve not made this Lisp different to confuse beginners. I’ve made it different because different is good.

If you are looking to learn about the semantics and behaviours of conventional Lisps, and how to program them, this book may not be for you. What this book offers instead is new and unique concepts, self expression, creativity, and fun. Whatever your motivation, heed this disclaimer now. Not everything I say will be objectively correct or true! You will have to decide that for yourselves.