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

(norvig.com)

82 points | by tosh 3 hours ago

11 comments

  • 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 2 hours ago

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

      • timonoko 32 minutes 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

        • 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 2 hours ago

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

          • timonoko 51 minutes 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 49 minutes ago

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

          • tosh 3 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?
                    • NooneAtAll3 15 minutes ago

                          ( aar
                            (bar1 1 2 3)
                            (bar2 1 2 3)
                            (bar3 
                               (car1 2 3)
                               (car2)
                               (car3)
                            )
                          )
                      
                      vs

                      (aar (bar1 1 2 3) (bar2 1 2 3) (bar3 (car1 2 3)(car2)(car3)))

                      • irishcoffee 1 hour ago

                        Emacs vs vim, go!

                      • eska 2 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.

                  • 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 3 hours ago

                      Appreciated the title xD

                      • joshuamorton 2 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 2 hours ago

                          (2010)?

                          • RedCinnabar 1 hour ago

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

                            • Crespyl 1 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 1 hour 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 1 hour ago

                                How do you mean “these kind”?

                                • RedCinnabar 1 hour 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 30 minutes 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 1 hour ago

                                  How so?