Build Your Own Lisp
50 comments
·August 5, 2025gorgoiler
metalliqaz
I poked around on those links and I have yet failed to find any use of this Lisp in that font project. Looks like he just built everything with Javascript
staplung
As others have pointed out, this is as much about learning C as it is about making a Lisp.
If you're interested in the latter, Peter Norvig has a little project that builds a stripped down Scheme interpreter in python. Takes some shortcuts, provides only a few functions (about 30) to its environment and only recognizes 5 special forms (`quote`, `if`, `define`, `set!`, and `lambda`) but the whole thing is less than 150 lines and very informative if you're new to that kind of thing.
cardanome
Don’t Build Your Own Lisp: https://gist.github.com/no-defun-allowed/7e3e238c959e27d4919...
Just so people are aware of it. It is not a good source if you want to learn how to make a lisp that could scale beyond a toy.
You can still learn a bit of C and get a taster of how to make a language, just be aware that some stuff you learn will hold you back in the long term.
Fraterkes
I’m sure the author of this is actually a nice person, but this is the first time I’ve actually seen a lisper being smug and obnoxious in the way I’ve seen people satirize a thousand times.
wk_end
Compared to much of what went on comp.lang.lisp this is pretty gentle. Based on the impression it gives of the book, possibly more gentle than it deserves!
BalinKing
With the exception of one or two sentences, it sounded pretty neutral to me... maybe I just didn't read it closely enough? The "dogmatism" of the technical criticism (assuming the post is accurate) really does seem justified to me—e.g. if the book uses dynamic scoping without even a disclaimer like "this is a bad idea, but we're doing it for simplicity", that alone makes it a bad recommendation for beginners IMO.
cardanome
I think the issue is that the topic comes up quite often as seen by the author needing to create the gist. It easy to come across as a bit of "smug and obnoxious" when you explain something for the xth time.
I remember chatting with them years ago and they were pretty friendly. But yeah Lisp does have a specific culture and it can put people off thought I personally never encountered any bad apples.
Fraterkes
I checked some of her other stuff and she seems great! I just wouldn’t want to argue with her about Lisp I think.
KerrAvon
I don't know, it doesn't seem overly smug to me. It seems borne of experience and helpfulness.
"And a parser generator is very overkill for a Lisp parser - just use recursive decent!" -- it's interesting that, as simple as Lisp is to parse, this is the same advice you'd get from experienced C/C++ compiler writers, from modern Clang to Stroustrup in 1993.
Arch-TK
You shouldn't use it to learn C either. It's full of bad C.
freilanzer
That sounds horrible. What are better resources?
stevekemp
MAL, the original "make a lisp", is a bit terse on details but gives you freedom to use different languages, and yet still provide a rough blueprint:
Discussed here, a few times:
dang
Thanks! Macroexpanded:
Mal – Make a Lisp - https://news.ycombinator.com/item?id=26924344 - April 2021 (40 comments)
Mal – Make a Lisp, implemented in 79 languages - https://news.ycombinator.com/item?id=21670442 - Nov 2019 (11 comments)
Mal – Make a Lisp, in 68 languages - https://news.ycombinator.com/item?id=15226110 - Sept 2017 (69 comments)
Make your own Lisp - https://news.ycombinator.com/item?id=13967401 - March 2017 (32 comments)
Mal – Make a Lisp - https://news.ycombinator.com/item?id=12720777 - Oct 2016 (1 comment)
Make a Lisp in Nim - https://news.ycombinator.com/item?id=9145360 - March 2015 (44 comments)
Make a Lisp - https://news.ycombinator.com/item?id=9121448 - Feb 2015 (41 comments)
Lisp implemented in under 1K of JavaScript - https://news.ycombinator.com/item?id=9109225 - Feb 2015 (16 comments)
cardanome
MAL is pretty good, albeit less hand-holding: https://github.com/kanaka/mal
Writing a Lisp in Ocaml: https://bernsteinbear.com/blog/lisp/00_fundamentals/
Not Lisp-specific but Crafting Interpreters is also great: https://craftinginterpreters.com/
hajile
I'd say that the best is probably the book "Lisp in Small Pieces".
Be aware that it's some 500 pages and makes several interpreters then a couple of compilers as I recall. If you read it though, you'll come out the other end with a pretty good understanding of how lisp implementations actually work.
axblount
Lisp In Small Pieces by Christian Queinnec
It takes a very thoughtful approach to introducing an increasingly complex Scheme implementation. I doesn't shy away from the complexity that many LISP implementation tutorials try to push under the rug.
teunispeters
I started from https://github.com/videogamepreservation/abuse which ... well, isn't perfect but it IS fun and the original game was, too.
OhMeadhbh
I just nano-blogged my thoughts about this yesterday: https://BI6.US/CO/N/20250803.HTML#/080401
Philpax
Microblogs are 200-500 characters, so I was expecting a nanoblog to me to be an order of magnitude less than that :sweat_smile:
dang
Related:
Build Your Own Lisp - https://news.ycombinator.com/item?id=36103946 - May 2023 (12 comments)
Learn C and build your own Lisp (2014) - https://news.ycombinator.com/item?id=35726033 - April 2023 (45 comments)
Learn C and build your own Lisp (2014) - https://news.ycombinator.com/item?id=27598424 - June 2021 (86 comments)
Learn C and Build Your Own Lisp (2014) - https://news.ycombinator.com/item?id=17478489 - July 2018 (86 comments)
Learn C and build your own Lisp - https://news.ycombinator.com/item?id=10474717 - Oct 2015 (49 comments)
Learn C and build your own Lisp - https://news.ycombinator.com/item?id=7530427 - April 2014 (145 comments)
lskfiep
This is MUCH more than a 'Build Your Own Lisp'. To the point of almost being anything but.
This is an amazing resource for getting started with learning C by making your own "programming language", independent of any Lisp conventions.
For me, the most 'lispy' aspect of 'making your own lisp' is prebaked by the author with their using their own prebuilt parser library 'mpc'. (I was unable to find a link to the source in the book, so https://github.com/orangeduck/mpc )
I was unable to find any instance of 'car' or 'cdr' or 'caddar' and their like, which I feel is the real 'build your own lisp' epiphany.
https://en.wikipedia.org/wiki/CAR_and_CDR
The parser is so widely, and wildly, useful that it is independent of notation style, for instance, lisp's nearly ubiquitous 'polish notation'. (or its variants, for instance, 'cambridge polish notation')
Perfect example:
Under 'Chapter 9: Reading Expressions':
> Don't Lisps use Cons cells?
> Other Lisps have a slightly different definition of what an S-Expression is. In most other Lisps S-Expressions are defined inductively as either an atom such as a symbol of number, or two other S-Expressions joined, or cons, together.
> This naturally leads to an implementation using linked lists, a different data structure to the one we are using. I choose to represent S-Expressions as a variable sized array in this book for the purposes of simplicity, but it is important to be aware that the official definition, and typical implementation are both subtly different.
https://www.buildyourownlisp.com/chapter9_s_expressions#Read...
This is an awesome educational resource.
I think I would promote it more broadly than "Build Your Own Lisp".
netbioserror
Unfortunately, part of the pragmatic usefulness of newer Lisps (Clojure and Janet) is the abandonment of CAR and CDR in favor of efficient distinct data structure types backed by efficient bases (tries, arrays, arraylists, hashmaps) and a focus on homoiconicity as the winning feature, separated forcefully from the idea of linked lists and CAR/CDR.
rscho
> efficient distinct data structure types backed by efficient bases
...do not require abandoning CAR and CDR, I think. See all other lisps having vectors, hashmaps, etc. Perhaps you're talking for code representation ? But I don't think that true for all 'traditional' lisps either. Also, there's been some innovation regarding lists: https://docs.racket-lang.org/reference/treelist.html
munificent
I'm honestly not sure why this sentence starts with "unfortunately".
Linked lists are comically inefficient on modern hardware and naming two of your fundamental operations based on CPU instructions from a chip from the 60s is not what I would call good API design.
spauldo
1954, actually. But it's a minor thing. You don't need to know anything about the IBM 704 to write Lisp. A cons cell is a specific data structure and its components have specific, if unusual names. There's a lot of unintuitively named symbols in Lisp that are better targets for criticism than car and cdr.
kentrado
I don't well understand this. How is clojure more efficient than common lisp?
Would you explain further?
netbioserror
From a compute standpoint I guess I'm wrong. But from a modeling power perspective, I definitely prefer the clarity and uniformity of Clojure's standard library functions. Maybe that has something to do with its distinct data types, maybe not.
tnlogy
Someone seems to have saved my old self-compiling scheme-to-c compiler in about 1k lines of scheme code. https://github.com/veqqq/llvm_scheme/blob/main/compile.ccode... (also an llvm version)
Maybe I should read and compare it. Mine was a really slow Poc to inspired by SICP, is that book still used in courses somewhere?
coderatlarge
i’m grateful to the author for making their work available online for free.
i once did an exercise like this myself (just the code not the book) for fun and found it extremely gratifying even though the code does not survive and never made it into any of my other projects as i had hoped at the outset.
mine got to be around 5 kloc with all the error handling but i wasn’t optimizing for keeping it short. i’m impressed by the many super brief ones that others with deeper understanding have built.
the point of view that this is really about learning C might have been buttressed further by starting with an existing super brief personal lisp and reading through that in a structured way; something that i personally would still like to do and that i semi-resorted to when debugging my way through the eval of the y-combinator which was one of the moments that exposed my poor design choices and the flaws i wasn’t cognizant of when doing simple expression evaluation. building a proper test harness was also a big deal as i went which seems like a highly relevant bit to highlight in a journey like this.
some references to existing high-quality short personal lisps and schemes might also be a welcome addition.
adz5a
Is there a resource which compares Lisps (expressiveness, limitations, available special forms, ...)? I often read about lisp 1 and 2.0, clojure being a lisp 1.5 (because of the callable keywords if iirc).
Dabbling into llms I think that lisps could be very interesting format to expose tools to llms, ie prompting a llm to craft programs in a Lisp and then processing (by that I mean parsing, correcting, analyzing and evaluating the programs) those programs within the system to achieve the user's goal.
Jtsummers
> lisp 1 and 2.0
Do you mean Lisp-1 and Lisp-2 as in the number of namespaces?
https://dreamsongs.com/Separation.html - Goes into depth on the topic including pros and cons of each in the context of Common Lisp standardization at the time (ultimately arguing in favor of Lisp-2 for Common Lisp on grounds of practicality, but not arguing strictly for either in the future).
Common Lisp was a, more or less, unification of the various Lisps, not Scheme, that had developed along some path starting from Lisp 1.5 (some more direct than others). They were all Lisp-2s because they all kept the same Lisp 1.5 separation between functions and values. Scheme is a Lisp-1, meaning it unifies the namespaces. The two main differences you'll find are that in CL (and related Lisps) you'll need to use `funcall` where in Scheme you can directly use a function in the head position of an s-expr:
(let ((f ...)) ;; something evaluating to a function
(f ...)) ;; Scheme
(funcall f ...)) ;; Lispcodr7
I've been working this problem from different angles for a while now:
nyrikki
I may be old. But use to use the pure Lisp Chatlin included in C with his papers to learn languages a few times.
Not as complete as this version of the language, but apparently ~300 lines of even REXX was enough although I never tried REXX.
golly_ned
Are there any such build-a-lisp books/guides using modern c++?
dark-star
Like most of these tutorials, this stops right where things get interesting. Taill-Call Optimization, Continuations, CPS, Call/CC... those are the things that are tricky to implement and without those the language is only a toy language.
Then again, creating a toy-language is a worthwhile goal in itself, so kudos to everyone who follows this through to the end
I learned recently that the creator of the Iosevka typeface did so using their own Lisp implementation.
The typeface:
https://github.com/be5invis/Iosevka
The language:
https://github.com/be5invis/PatEL
Their tool which they used to build the language:
https://github.com/be5invis/patrisika
These kinds of projects are deeply inspirational. Striving to achieve one percent of this output would be enough for me. Knowing there are people like Belleve / Renzhi Li and their team in the world -- that I might be able to do something like what they do if I, too, try hard -- is what makes me get out of bed in the morning. It is incredible that there are people like them, doing what they do, and sharing it freely. Thank you so much.
PS: Re: inspo: Hope 16 is next week :D https://www.hope.net/pdf/hope_16_schedule.pdf