(How to Write a (Lisp) Interpreter (In Python)) (2010)

ttosh about 4 hours ago 35 commentsRead Article on norvig.com

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dang•5 minutes ago

Is it classics day or something? (Fine with us!)

(How to Write a (Lisp) Interpreter (In Python)) (2010) - https://news.ycombinator.com/item?id=39665939 - March 2024 (91 comments)

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(How to Write a (Lisp) Interpreter (in Python)) - https://news.ycombinator.com/item?id=1745322 - Sept 2010 (39 comments)

chombier•about 3 hours ago

If you ever wondered how to write a programming language, this is probably the best resource to get started (and then of course Crafting Interpreters).

See also part 2 https://norvig.com/lispy2.html

embedding-shape•13 minutes ago

I've always found MAL ("Make-A-Lisp" https://github.com/kanaka/mal) a bit more approachable, probably because I was out after creating my own programming language before I've written much Python. It's language agnostic, and really easy to follow along with most programming languages out there, explaining everything as you progress.

That it's language agnostic and somehow matters feels weird now a lot of time (and experience I suppose) afterwards, but back when I only knew 1-2 languages by heart, also having to face understanding Python at the same time from Norvigs guide/reference made it slightly more complicated for me.

I use this as a litmus test now when coming across new languages (implementing MAL in the new language), as it's such an easy approach to practically test large parts of the new language, and there is always host-language-specific tricks you can learn along the way.

zahlman•about 3 hours ago

(how-to in-python (write (interpreter lisp)))

consumer451•about 3 hours ago

Yes, but to be fair, you only have a couple minutes to fight the HN title regex.

timonoko•about 1 hour ago

I actually perfected the Norvig Lisp at one time. It has compiler to python and just everything. Those very few here that can actually read code, understand why this project soon exploded into biggest piece of odorous excrement.

https://github.com/timonoko/nokolis.py

tosh•about 4 hours ago

I can't recommend highly enough to implement a simple lisp (or a forth).

Illuminating experience and it will also help you see (among many other things) the parentheses in a different light.

stdatomic•about 3 hours ago

First day of paradigms course in the 2000s and prof says "if your opinion of Scheme is too many parentheses, then you're an idiot."

Needless to say that was my opinion and every day I think, more and more, how right he was.

(later I did make some gui apps that included scripting and chose s-expr syntax because of how simple it is to implement it)

bananaflag•about 3 hours ago

There are two problems with Lisp parentheses in my opinion:

1) Humans are not that equipped to handle that level of nesting without some other aid, this is why Lisp code is usually indented.

2) Parentheses aren't just about grouping, and this is unintuitive. For example, x is not the same as (x). This is a bit like in set theory where x is not the same as {x}, but parentheses do not look like the kind of sign that would work like that.

jimmypk•about 1 hour ago

@bananaflag, the x versus (x) distinction is also what makes this evaluator so small: the AST uses atom versus list as the dispatch boundary, so grouping and application deliberately share syntax. An infix parser moves that complexity into precedence and associativity rules; it does not eliminate it. Indentation is still essential, but that is a tooling and display issue rather than a grammar issue.

NooneAtAll3•about 3 hours ago

main problem isn't brackets themselves - it's that they're too on the right

had brackets been displayed as curly braces in C - everything would look much more manageable

phpnode•about 3 hours ago

so, instead of

    (foo (bar (1 2 3))

you'd prefer

is that right?

eska•about 3 hours ago

I changed my opinion about parens when I stopped formatting like C, and used indent rather than parens to denote blocks. That is, a large amount of them at the end is totally fine.

azhenley•about 3 hours ago

Writing a Lisp is one of my favorite projects. I try to do it every year or two, taking a different approach each time.

onraglanroad•about 3 hours ago

The one where you replaced parentheses with the crying laughing emojis was definitely the worst.

librasteve•about 3 hours ago

or you could just use Raku and its “surprisingly good lisp impression”:

https://www.codesections.com/blog/raku-lisp-impression/

urcite_ty_kokos•about 4 hours ago

Appreciated the title xD

joshuamorton•about 3 hours ago

There are edge cases where this fails, but `def parse(s): return json.loads('['+re.sub('([")])\s*(["(])','\g<1>,\g<2>',re.sub('[^()\s]+','"\g<0>"',s)).replace('(','[').replace(')',']')+']')` is a surprisingly robust lisp parser.

e12e•about 3 hours ago

(2010)?

RedCinnabar•about 2 hours ago

Man these kind of resources have aged really bad in the age of AI.

Crespyl•about 2 hours ago

Why would AI make these age worse than, say, libraries or languages becoming obsolete?

I don't think a good learning resource gets worse just because there's a newer alternative.

RedCinnabar•about 2 hours ago

> I don’t think a good learning resource gets worse[...]

Probably not, but they become irrelevant. The other day I found an old programming book at my parents’ and while it was still a terrific resource, I couldn’t image anyone learning a language from a book nowadays.

AI is doing the same thing but 100 times effectively than anything else.

incanus77•about 2 hours ago

How do you mean “these kind”?

RedCinnabar•about 2 hours ago

Blog tutorials, guides, programming books and youtube tutorials. They are completely irrelevant in a time where you have a personal tutor willing to explain every single detail of a subject.

macintux•about 1 hour ago

That's like saying your grandfather is irrelevant now that he's spawned children and grandchildren. Good luck to those personal tutors without this source material.

jgalt212•about 2 hours ago

How so?

timonoko•about 1 hour ago

One of those exercises that are now just boring, because AI does it better.

My Lisp from 1975 was actually used in real world and highly lucrative. Gemini could read the source code, but it told that my code was piece of shit and cannot be implemented in 64-bit world without drastic changes, so it made an example. But that version was just too advanced and too complex as a study subject. There are already enuff good Lisps in the world, methinks.

Jtsummers•about 1 hour ago

Why did you replace your very similar comment with "--" just to post essentially the same thing again?