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Writing a Simple Programming Language from Scratch - Part 1

Evan Typanski on July 07, 2019

If you're a developer, you've used programming languages. They're awesome ways to make a computer do what you want it to. Maybe you've even dove de...

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Harvey Thompson • Jul 8 '19 • Edited

This is a very good introduction article. I've been working on and off on programming language design for 30 years or so, mostly as learning exercise. However in the past few years I've actually quit my job and done contract work so I can do it part-time, indeed writing a new full scope language (subtly named after myself even, ahhh hubris).

Here are my top three recommends:

Programming Languages: An Interpret Based Approach - Samel N Kamin - this isn't a well known book, but it totally re-ignited my interest. This book goes through various languages and their features and builds interpreters for them (in Pascal, it's an old book).
LLVM: Writing a Simple Programming Language - a step by step C++ tutorial on how to build a compiled language (using LLVM). You should basically use LLVM for the back-end, since that will save you hundreds of man-years of work and is open source. It's a well solved problem that is totally applicable to anything anyone can build. Clang is the C/C++/ObjectiveC front-end.
Types and Programming Languages: Benjamin C Pierce - this is perhaps heavy mathematically, however you can skip those parts and still understand the concepts. If you want to properly understand type systems and do it properly, this book has it all. New languages like Scala, Kotlin, Swift (and others such as Typescript) are beginning to include things like set-theoretic type systems (optionals, unions, intersections). This book has been incredibly influential for myself, and will lead you down many good rabbit holes.

My other recommendation, if you get more serious, is to find academic papers relating to compilers and technology to see what's out there. Many are summaries and/or improvements/extensions of other works, but it does eventually lead you to the gold nugget papers. After a week of searching I found one academic paper (with a sequel) which basically allowed me to leap in understanding several years ahead - why waste time working something out when somebody way smarter has done it for you.

It's also true that learning about how compilers and interpreters work really elevates your understanding of software engineering and programming. There's a reason why most undergraduate degrees have a "Compilers" course.

My "record" for implementing a language from scratch was one day, with less than 100 lines. I used it to write an interactive and offline test suite when I rewrote Unix kernel network APIs. It was a Lisp interpreter, which in general has very limited lexical, syntactical and semantic definitions, but is a powerful: see Clojure and Emacs for examples of this taken further.

Evan Typanski • Jul 9 '19

Awesome, I really appreciate the reply! I'm still learning and love having the opportunity to move forward, so I really appreciate the references. Being part 1 I was very much planning on generating LLVM. Secretly the reason I wrote this was so I could dive a lot further into LLVM, as I already have done the flex/bison stuff a few times before, but this part got pretty in depth so I cut the post a little short.

I'm curious how working with compilers and language design works in the job market, though. I see companies like Google and Mozilla making programming languages, but most of that seems like R&D and hard to get into. Do you know how marketable an interest in compilers?

Harvey Thompson • Jul 9 '19

I look forward to part 2!

As for the job market, I'm not sure that there's a huge specific market for R&D jobs in building compilers. I could be wrong. My actual expertise is fairly varied, but in the past 15 years has been in games development. Know how to build interpreters and compilers is usually indirectly useful; you get to ramp up a little quick when using new languages or compilers. Usually there are occasional opportunities in many companies to apply the techniques or even build languages (eg. integrate Lua or Lisp into a game). Such knowledge rounds out a decent resume.

Lakin Mohapatra • Aug 20 '23

Thanks for sharing

Jason Barr • Dec 6 '19

This is kinda out of nowhere since it's been a while, but are there any plans to write the next article? I totally understand getting busy and/or losing track of ideas like this (I'm working on an occasionally-updated introduction to computer science in JavaScript series that hasn't been published to in over a month) but I would love to see the next steps.

Evan Typanski • Dec 6 '19

Yes! I've been periodically working and making decent progress. Reason I made the post was to learn more about LLVM/backend work, so I'd rather know I have a solid understanding before trying to teach it, which has taken a bit longer than I'd thought. I'll have more time soon, but definitely not forgotten

Jason Barr • Dec 6 '19

Nice! I'll follow you so I'll get a notification when you're able to put it together. I definitely know about things taking longer than I thought they would.

I found this article because I'm in the process of building a quick-and-dirty interpreter for my own language (in JavaScript because it's easy and it's the language I know best) just for fun, and a lot of what you wrote here has been helpful.

I'll probably write a fuller implementation in another language once I have a working prototype for myself, and C++ is a possibility. I don't know C++ very well though, so it would be quite a challenge.