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

(norvig.com)

69 points | by tosh 3 hours ago ago

32 comments

  • timonoko 8 minutes ago

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

    Gemini did write Lisp-1 interpreter in Linux-assembly the other day. It was ready to implement garbage collection and compiler and all shit, but that was just depressing from human point of view.

    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 6 minutes ago

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

  • chombier 2 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

  • zahlman 2 hours ago

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

    • consumer451 an hour ago

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

  • azhenley 2 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 an hour ago

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

  • tosh 2 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 2 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 2 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.

      • NooneAtAll3 2 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 2 hours ago

          so, instead of

              (foo (bar (1 2 3))
          
          you'd prefer

              {
                foo {
                  bar {
                    1
                    2
                    3
                  }
                }
              }
          
          is that right?
        • eska an hour 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.

  • librasteve 2 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 2 hours ago

    Appreciated the title xD

  • joshuamorton an hour 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 2 hours ago

    (2010)?

  • timonoko an hour ago

    [fagged]

    • genxy an hour ago

      There is always someone better than you at almost everything you do, this is statistical reality.

      If all you care about is the artifact and not the path, there is no reason to do anything.

      Use the tool to better yourself, your understanding and push the limits of what is possible. If a Lisp in assembly with GC is now hello world, change what a hard project is.

      I see this attitude a lot, and I think it is rooted in a sort of self-centered elitism. Anyone can do it, so why do it? Instead you could have the AI teach you how to implement it yourself with a deep understanding that no human, even if you paid them, would put up with.

      But sure, get depressed. But why tho?

    • tosh an hour ago

      is learning how to accomplish or understand something boring

      just because someone or something else does it better?

    • abecedarius 27 minutes ago

      It's funny, in the 8-bit days a lot of us learned programming for its own sake without much expectation it'd be lucrative. Took ~50 years to get back to that spirit as the default.

    • Lyngbakr an hour ago

      It depends why you're doing it. Are you doing it for the product or the process? (Of course, they're not mutually exclusive.) I do it for the fun of building, in which case AI is irrelevant.

    • chamomeal an hour ago

      I mean it’s still worth doing, even if AI can do it. But I definitely empathize with that bit of AI ennui.

  • RedCinnabar an hour ago

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

    • Crespyl an hour 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 33 minutes 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 an hour ago

      How do you mean “these kind”?

      • RedCinnabar 40 minutes 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.

    • jgalt212 an hour ago

      How so?