WEBVTT captioned by sachac NOTE Intro 00:00.000 --> 00:00:00.014 Hi, my name is Eduardo Ochs 00:00:00.015 --> 00:00:05.020 and the title of this talk is 00:05.020 --> 00:07.840 REPLs in Strange Places: Lua, LaTeX, 00:07.840 --> 00:10.440 LPeg, LPegRex, and TikZ. 00:10.440 --> 00:13.400 I'm the author of an Emacs package called eev, 00:13.400 --> 00:17.280 and this is a talk at the EmacsConf 2023, 00:17.280 --> 00:21.560 that is happening in December 2023 at the Internet. NOTE Diagrams 00:21.560 --> 00:00:24.243 This is one of the examples of diagrams 00:00:24.244 --> 00:00:25.920 that we are going to see. 00:25.920 --> 00:28.400 Let me show how I generated it. 00:28.400 --> 00:33.600 One second, I have to use a smaller font here. 00:34.560 --> 00:39.080 This is a file called parse32.lua. 00:39.080 --> 00:42.600 Let me go back to this block of tests again. 00:42.600 --> 00:45.520 Now, if I run this, 00:46.720 --> 00:51.520 we get these outputs here at the right. 00:51.520 --> 00:53.800 Then in this line here, 00:53.800 --> 00:55.420 it generates a PDF, 00:55.420 --> 00:57.780 and if I type `F8` here, 00:57.780 --> 01:02.560 it shows the PDF in the lower right window. NOTE eev 01:03.320 --> 01:08.920 Let me start by explaining briefly what is eev. 01:08.920 --> 00:01:10.889 First, it's something 00:01:10.890 --> 00:01:14.560 that appeared by accident in the mid 90s. 01:14.560 --> 01:20.640 I explained this story in my presentation at EmacsConf 2019. 01:20.640 --> 01:25.420 It's an Emacs package that is part of ELPA. 01:25.420 --> 01:28.720 It has at least 10 users. 01:28.720 --> 01:32.480 Those are the ones that I know by name. 01:32.480 --> 01:36.960 eev means "Emacs, execute verbosely". 01:36.960 --> 00:01:38.847 eev is something that treats eval-last-sexp 00:01:38.848 --> 00:01:43.400 as the central feature of Emacs. 01:43.400 --> 01:47.280 eev blurs the distinction between programmers and users, 01:47.280 --> 01:49.960 and it replaces the slogan, 01:49.960 --> 01:52.360 "users should not be forced to see Lisp" 01:52.360 --> 01:55.280 (that is something that Richard Stallman told me once), 01:55.280 --> 01:59.240 by "users should see Lisp instead of buttons," 01:59.240 --> 02:03.400 and "new users should see Lisp in the first five minutes." 02:03.400 --> 02:08.160 I'm going to show some examples of that soon. 02:08.160 --> 00:02:11.565 eev uses code in the comments a lot 00:02:11.566 --> 00:02:14.120 and also tests in comments. 02:14.120 --> 00:02:16.781 I changed my way of presenting it, 00:02:16.782 --> 00:02:19.190 and it became very REPL-centric 00:02:19.191 --> 00:02:22.200 in the last few years, in the sense that 02:22.200 --> 00:02:26.460 I start by explaining its main features 00:02:26.461 --> 00:02:29.520 by its support for REPLs. 02:29.520 --> 00:02:32.078 eev supposes that we want to keep 00:02:32.079 --> 00:02:34.560 executable notes of everything. 02:34.560 --> 02:37.800 I'm also going to show examples of this in a second. 02:37.800 --> 02:42.120 eev has lots of videos for people who hate videos, 02:42.120 --> 00:02:44.270 and it tries to do everything 00:02:44.271 --> 00:02:47.640 with very little magic and without black boxes. 02:47.640 --> 02:51.360 I'm going to explain many of these things very soon. NOTE Another figure 02:51.360 --> 02:58.200 This is a figure that I'm going to show in detail soon 02:58.200 --> 03:01.640 that is about something important about Lua. 03:01.640 --> 03:03.400 Oops, the font is very bad now, 03:03.400 --> 03:05.200 so let me change the font. 03:05.200 --> 03:07.760 The figure is this one. 03:09.880 --> 00:03:12.935 What most people do when they visit a file 00:03:12.936 --> 00:03:15.280 with something interesting in it, 03:15.280 --> 03:18.360 is that they just go there and they set a bookmark there, 03:18.360 --> 03:22.640 or they put the position in the register. 03:22.640 --> 00:03:29.781 But I prefer to keep links 00:03:29.782 --> 00:03:30.221 to everything that is interesting 00:03:30.222 --> 00:03:30.480 as an Elisp hyperlink. 03:30.480 --> 00:03:34.236 For example, this is an Elisp hyperlink to the file 00:03:34.237 --> 00:03:36.520 that goes to this anchor here, 03:36.520 --> 03:39.280 and to this string after this anchor. 03:39.280 --> 00:03:43.388 This is a variant that opens that file 00:03:43.389 --> 00:03:46.760 in the window at the right here, 03:46.760 --> 03:53.640 and this is a sexp that changes the font. 03:53.640 --> 03:57.880 I have a command with a very short name that does that, 03:57.880 --> 04:03.680 but I prefer to keep that as a one-liner. 04:03.680 --> 00:04:04.281 About the videos, we can see 00:04:04.282 --> 00:04:11.440 the list of first-class videos of eev by executing this, 04:11.440 --> 00:04:14.190 `M-x find-1stclassvideos`, 00:04:14.191 --> 00:04:18.480 or by running this alias here, `M-x 1c`, 04:18.480 --> 04:21.160 and then what we see is this. 04:21.160 --> 04:25.560 The first sexp here regenerates this buffer, 04:25.560 --> 04:29.120 so we can make a mess here and then run this, 04:29.120 --> 04:34.120 and the original buffer is regenerated again in a clean way. 04:34.120 --> 00:04:36.951 Each of these things here 00:04:36.952 --> 00:04:41.960 opens a buffer with information about a video. 04:41.960 --> 04:45.320 Let me take a specific example here. 04:45.320 --> 00:04:50.278 This video here is about one of the ancestors of this talk 00:04:50.279 --> 00:04:52.800 that is a library that I wrote 04:52.800 --> 00:04:56.906 for creating diagrams in LaTeX 00:04:56.907 --> 00:05:03.000 using a package called [pict2e-lua] using REPLs. 05:03.000 --> 00:05:10.028 Anyway, the thing is that if we run a sexp like this one 00:05:10.029 --> 00:05:16.314 and we don't have a local copy of the video, 00:05:16.315 --> 00:05:19.581 eev will try to load the local copy 00:05:19.582 --> 00:05:20.560 and instead of doing that by asking something 05:20.560 --> 00:05:25.381 like "do you want me to download the local copy" 00:05:25.382 --> 00:05:29.240 blah, blah, blah, it simply opens a buffer like this. 05:29.240 --> 00:05:35.514 And if we don't have a local copy yet, 00:05:35.515 --> 00:05:37.220 it will open a buffer like this one, 00:05:37.221 --> 00:05:40.030 in which these things here in comments 00:05:40.031 --> 00:05:42.678 are links to the documentation. 00:05:42.679 --> 00:05:45.780 This thing here explains the idea 00:05:45.781 --> 00:05:50.278 of local copies of files from the internet. 00:05:50.279 --> 00:05:54.120 There are more details here and here, 00:05:54.121 --> 00:05:59.580 and this is a script that we can execute line by line. 05:59.580 --> 00:06:04.276 So instead of this script being hidden behind the button 00:06:04.277 --> 00:06:07.160 that we just press after a question 06:07.160 --> 00:06:10.708 like "do you want me to do something," blah, blah, blah, 00:06:10.709 --> 00:06:13.228 "yes or no?", the script is visible here 00:06:13.229 --> 00:06:15.380 and we can execute it step by step. 06:15.380 --> 00:06:22.457 It creates a terminal with a shell here in the right window 00:06:22.458 --> 00:06:26.988 and when we type `F8` in these lines here, 00:06:26.989 --> 00:06:30.360 the lines are sent to this line. 06:30.360 --> 00:06:33.842 So this is going to download a copy of the video, 00:06:33.843 --> 00:06:38.134 the wget says that I already have a copy of the video 00:06:38.135 --> 00:06:40.360 and its subtitles and so on. 06:40.360 --> 00:06:45.739 And after getting a copy of the video 00:06:45.740 --> 00:06:52.960 we can run this exp here and it displays the video. 06:52.960 --> 00:06:55.486 I said that eev has lots of videos 00:06:55.487 --> 00:06:57.435 for people who hate videos. 00:06:57.436 --> 00:07:00.046 The idea is that very few people 00:07:00.047 --> 00:07:03.081 are going to watch the videos in real time. 00:07:03.082 --> 00:07:07.642 Most of the people that I know, or most of the people 00:07:07.643 --> 00:07:10.790 that are interested in eev in some way, 00:07:10.791 --> 00:07:14.320 they are going to watch just small sections of the video. 00:07:14.321 --> 00:07:17.574 Most of the time, they are just going to 00:07:17.575 --> 00:07:19.940 read the subtitles of the video. 07:19.940 --> 00:07:22.531 For each one of the videos 00:07:22.532 --> 00:07:25.295 we have a page about the video... 00:07:25.296 --> 00:07:29.673 Let me see if I have internet here... 00:07:29.674 --> 00:07:34.901 This is a page. Usually these pages 00:07:34.902 --> 00:07:38.427 have a link to another page, 00:07:38.428 --> 00:07:43.890 the page that has all the subtitles of the video, 00:07:43.891 --> 00:07:48.587 wherever. In this one, it's not so visible. 00:07:48.588 --> 00:07:52.001 Anyway, there are several ways of accessing 00:07:52.002 --> 00:07:53.963 the subtitles of the video. 00:07:53.964 --> 00:07:58.632 One of the ways is by running this sexp here 00:07:58.633 --> 00:08:01.064 that opens a file in Lua. 00:08:01.065 --> 00:08:05.440 That is what I use to generate the subtitles. 08:05.440 --> 00:08:10.368 By the way, each one of these things here 00:08:10.369 --> 00:08:14.680 is hyperlinked to a position of the video. 08:14.680 --> 00:08:21.280 If I type this, it goes to that position. 00:08:21.281 --> 00:08:24.580 Anyway, let me go back. 08:24.580 --> 00:08:28.557 So the tutorials of eev, the intros of eev 00:08:28.558 --> 00:08:32.350 that start with `find-` and end with `-intro`, 00:08:32.351 --> 00:08:35.332 they have lots of blocks that say 00:08:35.333 --> 00:08:37.612 video links like this one. 00:08:37.613 --> 00:08:41.972 These blocks have links to positions in videos. 00:08:41.973 --> 00:08:46.332 If we don't have a local copy of the video yet, 00:08:46.333 --> 00:08:49.015 the thing shows us a script 00:08:49.016 --> 00:08:52.560 that lets us download the local copy. NOTE eev-wconfig, magic, and black boxes 08:52.560 --> 00:08:57.440 I said that I was going to explain 00:08:57.441 --> 00:09:01.855 what I mean by magic and black boxes, 00:09:01.856 --> 00:09:03.799 this is something that I've been trying 00:09:03.800 --> 00:09:05.111 to explain for a long time 00:09:05.112 --> 00:09:08.761 and I think that I got a very good explanation about that 00:09:08.762 --> 00:09:12.348 in a video that I made about something called eev-wconfig 00:09:12.349 --> 00:09:17.943 that is a tool for configuring eev on Windows without magic, 00:09:17.944 --> 00:09:20.878 without buttons that do things, 00:09:20.879 --> 00:09:24.380 without explaining what they are doing. 09:24.380 --> 00:09:28.078 This is a part of the subtitles of the video. 00:09:28.079 --> 00:09:29.445 Let me read that. 00:09:29.446 --> 00:09:32.531 eev-wconfig is an attempt to solve the problem 00:09:32.532 --> 00:09:35.349 of how to install these things on Windows 00:09:35.350 --> 00:09:40.040 both without magic and with very little magic. 09:40.040 --> 00:09:44.941 Remember this slogan: "Any sufficiently advanced technology 00:09:44.942 --> 00:09:47.600 is indistinguishable from magic." 09:47.600 --> 00:09:51.433 Here in this video I'm going to use the term magic 00:09:51.434 --> 00:09:55.262 as a shorthand for sufficiently advanced technology 00:09:55.263 --> 00:09:58.944 that is something that is complex and non obvious 00:09:58.945 --> 00:10:01.920 and that is indistinguishable from magic 00:10:01.921 --> 00:10:05.840 in the sense of being almost impossible to understand. 10:05.840 --> 00:10:09.272 And I'm also going to use the term black box 00:10:09.273 --> 00:10:11.408 as a near synonym for magic 00:10:11.409 --> 00:10:15.217 and sometimes the term black box is more convenient 00:10:15.218 --> 00:10:17.488 even though it's a bit longer, 00:10:17.489 --> 00:10:21.333 it has more letters because when I use the term black box 00:10:21.334 --> 00:10:23.521 it invites us to use expressions 00:10:23.522 --> 00:10:27.872 like opening the black box 00:10:27.873 --> 00:10:34.800 and I'm going to use that expression a lot. 10:34.800 --> 00:10:40.899 Now let me try to explain what is. Sorry, 00:10:40.900 --> 00:10:44.240 let me change the font. NOTE Lua 10:44.240 --> 10:45.240 What is Lua? 10:45.240 --> 00:10:48.645 Lua is a minimalistic language 00:10:48.646 --> 00:10:53.040 in the sense of battery is not included. 10:53.040 --> 00:10:57.987 It uses associative tables for most of its data structures. 00:10:57.988 --> 00:11:00.874 It's so minimalistic 00:11:00.875 --> 00:11:05.147 that the default print function 00:11:05.148 --> 00:11:11.960 when we create an associative table and we ask it to print-- 11:11.960 --> 00:11:14.914 we ask print to print an associative table-- 00:11:14.915 --> 00:11:17.600 it just prints the address of the table. 11:17.600 --> 00:11:20.902 Here are some examples. Here is a table 00:11:20.903 --> 00:11:23.296 and when we ask to print it, 00:11:23.297 --> 00:11:28.200 it just says that it's the table at this address here. 11:28.200 --> 00:11:30.893 One of the things that most people do 00:11:30.894 --> 00:11:33.586 when they start using Lua is that either 00:11:33.587 --> 00:11:36.313 they download a package with a print to printing function 00:11:36.314 --> 00:11:39.520 or they write their own print to printing functions. 11:39.520 --> 00:11:41.975 My own print to printing function 00:11:41.976 --> 00:11:44.450 is called PP with upper case letters, 00:11:44.451 --> 00:11:46.757 and it works like this. 00:11:46.758 --> 00:11:52.072 It prints associative tables in a way like this. 00:11:52.073 --> 00:11:54.125 It says that for the key 1, 00:11:54.126 --> 00:11:56.602 the value associated to it is 2; 00:11:56.603 --> 00:11:59.078 for the key 2, the value is 3; 00:11:59.079 --> 00:12:09.240 and for the key 3, the value is 5. 12:09.240 --> 00:12:12.379 When I started using Lua, one of my favorite languages 00:12:12.380 --> 00:12:16.623 was also a language that used associative tables a lot. 00:12:16.624 --> 00:12:20.339 It was called Icon. I had to write my own 00:12:20.340 --> 00:12:23.394 print to printing functions for Icon, 00:12:23.395 --> 00:12:29.425 so I just had to port my print to printing functions to Lua. 00:12:29.426 --> 00:12:34.350 My first version looked something like this. 00:12:34.351 --> 00:12:40.080 it just had some global functions. Lots of them actually. 12:40.080 --> 00:12:41.933 After a while, I rewrote it. 00:12:41.934 --> 00:12:44.503 I rewrote it again and again and again. 00:12:44.504 --> 00:12:48.397 This is one of the versions 00:12:48.398 --> 00:12:53.751 that is not even the default at this point. 00:12:53.752 --> 00:12:57.702 `tos` is for to string. This is a demo. 00:12:57.703 --> 00:13:02.905 It's very modular, so it's easy to replace parts of it 00:13:02.906 --> 00:13:06.567 or to toggle flags. This is an example. 00:13:06.568 --> 00:13:11.797 If I try to print the table of methods for a certain class-- 00:13:11.798 --> 00:13:16.245 I only need a smaller font--it prints the table like this 00:13:16.246 --> 00:13:18.510 with the names of the methods 00:13:18.511 --> 00:13:22.360 and then links to the source code of the functions. 13:22.360 --> 00:13:26.671 These links only make sense in Emacs and in eev. 00:13:26.672 --> 00:13:30.296 When we run a link like this one, 00:13:30.297 --> 00:13:34.013 it shows the source code and the window at the right. 00:13:34.014 --> 00:13:38.647 For some functions, the source code is three lines. 00:13:38.648 --> 00:13:42.320 For other ones, it's one line and whatever. 13:42.320 --> 00:13:44.149 Anyway, let me go back. 00:13:44.150 --> 00:13:47.490 Lua can be used in many different styles. 00:13:47.491 --> 00:13:52.240 Most people hate other people's styles. 13:52.240 --> 00:13:55.252 When I started using it in the year 2000, 00:13:55.253 --> 00:13:59.566 I learned most of the basic language in a single day. 00:13:59.567 --> 00:14:04.042 It was very similar to things that I was already using. 00:14:04.043 --> 00:14:08.388 Then I rewrote the mini language 00:14:08.389 --> 00:14:15.200 that I was using to generate the HTML for my pages in Lua. 14:15.200 --> 00:14:17.591 Actually, I had to rewrite it many times 00:14:17.592 --> 00:14:21.367 but the first version I certainly did 00:14:21.368 --> 00:14:25.740 in my first weeks or first months using Lua. 14:25.740 --> 00:14:29.653 In the beginning, I was just using it for writing programs 00:14:29.654 --> 00:14:32.876 that either didn't take any input at all 00:14:32.877 --> 00:14:36.727 because the input was already in the source file, 00:14:36.728 --> 00:14:39.400 or that worked as a Unix function: 14:39.400 --> 00:14:42.451 the Unix programs that would read files, 00:14:42.452 --> 00:14:49.560 process these files in some way, and output something. 14:49.560 --> 00:14:52.200 I mentioned the basic language here, 00:14:52.201 --> 00:14:55.625 I only learned how to use closures, meta tables, 00:14:55.626 --> 00:15:00.600 and coroutines many years later. 15:00.600 --> 00:15:02.588 In the beginning when I started using Lua 00:15:02.589 --> 00:15:04.199 it didn't have a package manager. 00:15:04.200 --> 00:15:08.299 It appeared later. It is called luarocks. 00:15:08.300 --> 00:15:13.180 It has had this package manager for several years. 15:13.180 --> 00:15:17.242 Most of the rocks for luarocks are poorly documented 00:15:17.243 --> 00:15:18.897 and hacker-unfriendly. 00:15:18.898 --> 00:15:22.079 You can't rely just on the documentation. 00:15:22.080 --> 00:15:25.188 You can't rely just on the source code, 00:15:25.189 --> 00:15:28.706 because--I mean, if you're a genius, of course you can, 00:15:28.707 --> 00:15:31.544 but for people who are either 00:15:31.545 --> 00:15:35.895 lazy or dumb or whatever like me, or unfocused, 00:15:35.896 --> 00:15:39.490 the source code is hard to understand 00:15:39.491 --> 00:15:41.760 and hard to tinker with. 15:41.760 --> 00:15:43.760 Some rocks are excellent. 00:15:43.761 --> 00:15:46.452 The best rocks are well documented, 00:15:46.453 --> 00:15:48.760 but they are hacker-unfriendly 15:48.760 --> 15:53.640 in the sense that I hope that I'll be able to explain soon. 15:53.640 --> 00:15:59.466 The best rocks use local variables and meta tables a lot, 00:15:59.467 --> 00:16:02.905 so if you are a beginner learning Lua 00:16:02.906 --> 00:16:08.245 you're not going to understand what their source codes do. 00:16:08.246 --> 00:16:10.960 They use lots of dirty tricks. NOTE Object orientation in Lua 16:10.960 --> 16:14.360 Let me talk a bit about object orientation in Lua. 16:14.360 --> 00:16:18.275 It can be done in many ways. The main book about Lua 00:16:18.276 --> 00:16:20.140 called Programming in Lua 00:16:20.141 --> 00:16:22.865 by one of the authors of the language 00:16:22.866 --> 00:16:24.729 called Roberto Ierusalimschy 00:16:24.730 --> 00:16:28.680 presents several ways of doing object orientation in Lua. 16:28.680 --> 00:16:31.386 I hated all of these ways, 00:16:31.387 --> 00:16:36.056 and also the ways that I tried from the rocks. 00:16:36.057 --> 00:16:37.933 Then I wrote my own way 00:16:37.934 --> 00:16:40.347 of doing object orientation in Lua. 00:16:40.348 --> 00:16:45.653 It's very minimalistic. It's in this file here eoo.lua. 00:16:45.654 --> 00:16:49.898 The main code is just these five lines here. 00:16:49.899 --> 00:16:56.400 Here's an example of how it works. 16:56.400 --> 00:17:03.001 We define a class vector with some meta methods. 00:17:03.002 --> 00:17:06.294 This meta method here will tell Lua 00:17:06.295 --> 00:17:10.867 what to do when the user asks to add two vectors. 00:17:10.868 --> 00:17:13.986 This one here tells Lua what to do 00:17:13.987 --> 00:17:18.888 when the user asks Lua to convert a vector to a string 00:17:18.889 --> 00:17:22.007 and whatever. This one is something 00:17:22.008 --> 00:17:25.580 that I'm going to explain in a second. 17:25.580 --> 00:17:25.580 Here we create a vector 00:17:25.580 --> 00:17:25.580 with these coordinates 3 and 4. 00:17:25.581 --> 00:17:25.580 Here we create another vector. 17:31.600 --> 00:17:33.030 If we print here, 00:17:33.031 --> 00:17:37.153 then Lua uses the function here in the `__tostring`. 00:17:37.154 --> 00:17:38.907 If we add two vectors 00:17:38.908 --> 00:17:42.653 it uses the function here in the `__add` meta method. 00:17:42.654 --> 00:17:45.044 If we run the method `norm`, 00:17:45.045 --> 00:17:51.680 it is defined here in the table index. 17:51.680 --> 00:17:57.675 Anyway, even with this thing being so small, 00:17:57.676 --> 00:18:04.617 I used to forget how it works all the time. 00:18:04.618 --> 00:18:08.200 Actually, I always forget how things work, 00:18:08.201 --> 00:18:11.347 and I have to remember them somehow. 00:18:11.348 --> 00:18:14.920 I have to have tricks for remembering, 00:18:14.921 --> 00:18:19.769 and tricks for summarizing things and diagrams, and so on. 00:18:19.770 --> 00:18:23.309 Every time that I forgot how this thing worked, 00:18:23.310 --> 00:18:25.460 I went back to the source code 00:18:25.461 --> 00:18:28.148 and then I looked at the diagrams, 00:18:28.149 --> 00:18:30.994 or, of course, the first time, 00:18:30.995 --> 00:18:33.800 I had to draw the diagrams. I run the examples. 00:18:33.801 --> 00:18:35.539 Of course, in the beginning 00:18:35.540 --> 00:18:37.503 I thought that the code was clear. 00:18:37.504 --> 00:18:39.737 My examples were very brief. 00:18:39.738 --> 00:18:43.565 So I had to rewrite the examples many times 00:18:43.566 --> 00:18:50.880 until they became let's say perfect. 18:50.880 --> 00:18:54.090 I was saying that Lua can be used in many ways 00:18:54.091 --> 00:18:58.403 and in my way of using Lua, in my favorite way, 00:18:58.404 --> 00:19:03.075 everything can be inspected and modified from REPLs 00:19:03.076 --> 00:19:06.817 like we can do in Emacs and in SmallTalk, sort of. 00:19:06.818 --> 00:19:09.436 In my favorite way of using Lua 00:19:09.437 --> 00:19:11.531 there's no security at all. 00:19:11.532 --> 00:19:17.460 Everything can be changed at all times. 19:17.460 --> 00:19:19.822 Of course, most people hate that. NOTE My init file 00:19:19.823 --> 00:19:22.185 My init file has lots of classes, 00:19:22.186 --> 00:19:24.701 and by the way, instead of 00:19:24.702 --> 00:19:28.636 keeping many small files with many things, 00:19:28.637 --> 00:19:33.000 I put lots of stuff in just one big init file. 19:33.000 --> 00:19:35.520 My init file has lots of classes, 00:19:35.521 --> 00:19:39.187 and lots of global functions and lots of cruft, 00:19:39.188 --> 00:19:43.700 so people hate that, of course. 19:43.700 --> 00:19:46.340 This is an example. 00:19:46.341 --> 00:19:52.415 This is the index at the top of my init file. 00:19:52.416 --> 00:19:57.541 The classes start here. Then we have some functions 00:19:57.542 --> 00:20:02.480 and then we have functions that load certain packages, 20:02.480 --> 20:06.580 and then we have cruft, whatever. 20:06.580 --> 00:20:08.923 Most people think that my style of using Lua 00:20:08.924 --> 00:20:10.122 is dirty and dangerous, 00:20:10.123 --> 00:20:14.287 and they wouldn't touch my Lua code with a 10 feet pole, 00:20:14.288 --> 00:20:15.968 but most of the things 00:20:15.969 --> 00:20:19.256 that I'm going to present here in this presentation 00:20:19.257 --> 00:20:23.050 are ideas that should be easy to port to other environments 00:20:23.051 --> 00:20:27.738 and other languages, especially the diagrams, 00:20:27.739 --> 00:20:31.000 so the code is not so important. NOTE LaTeX and LuaLaTeX 20:31.000 --> 00:20:34.640 Now let me talk a bit about LaTeX, LuaLaTeX, 00:20:34.641 --> 00:20:39.249 that is LaTeX with the Lua interpreter embedded inside 00:20:39.250 --> 00:20:43.182 and two ways of generating pictures in LaTeX: 00:20:43.183 --> 00:20:45.115 TikZ that is very famous, 00:20:45.116 --> 00:20:48.311 and Pict2e that is not very famous 00:20:48.312 --> 00:20:50.644 and that is very low level, 00:20:50.645 --> 00:20:53.840 and I think that not many people use. 20:53.840 --> 00:20:57.048 I said before that when I learned Lua, 00:20:57.049 --> 00:21:00.354 I realized that it was very good 00:21:00.355 --> 00:21:03.360 for writing literal languages. 21:03.360 --> 00:21:05.986 I was doing my PhD at the time 00:21:05.987 --> 00:21:09.969 and typesetting the diagrams for my PhD thesis 00:21:09.970 --> 00:21:11.240 was very boring. 21:11.240 --> 00:21:13.864 One of the things that I did was that 00:21:13.865 --> 00:21:15.720 I created a literal language 00:21:15.721 --> 00:21:19.340 for typesetting the diagrams for me. 21:19.340 --> 00:21:22.821 It was called Dednat because initially 00:21:22.822 --> 00:21:26.800 it only generated diagrams for natural deduction 21:26.800 --> 21:30.440 and then it had several versions. 21:30.440 --> 00:21:34.379 These are the slides from my presentation about Dednat6 00:21:34.380 --> 00:21:38.990 and Dednat6 is an extensible semi preprocessor 00:21:38.991 --> 00:21:43.691 for LuaLaTeX that understands diagrams in ASCII art 00:21:43.692 --> 00:21:49.034 in the sense that when I have a TeX file that has this, 00:21:49.035 --> 00:21:52.143 and when Dednat6 is loaded, 00:21:52.144 --> 00:21:55.708 when I get the right comments, 00:21:55.709 --> 00:22:00.342 Dednat6 interprets this block here 00:22:00.343 --> 00:22:05.095 as something that defines this diagram. 00:22:05.096 --> 00:22:07.828 It interprets this diagram here, 00:22:07.829 --> 00:22:10.643 this diagram in the comments here, 00:22:10.644 --> 00:22:16.432 as something that defines a diagram called `foo`, 00:22:16.433 --> 00:22:23.064 a deduction called `foo`, and it generates this code here 00:22:23.065 --> 00:22:28.867 so that we can just invoke the definition of the deduction 00:22:28.868 --> 00:22:31.720 by typing `\ded{foo}`. 22:31.720 --> 00:22:36.148 Dednat6 also supports another language 00:22:36.149 --> 00:22:40.579 for typesetting bidimensional diagrams with arrows and stuff 00:22:40.580 --> 00:22:43.122 for category theory and blah blah. 00:22:43.123 --> 00:22:46.100 The specifications of these diagrams 22:46.100 --> 00:22:53.865 look like this. Here is a very good example. 00:22:53.866 --> 00:23:00.940 This is a huge diagram. Sorry, one second. 23:00.940 --> 00:23:04.757 So the source code that generates this diagram here 00:23:04.758 --> 00:23:08.628 is just this thing at the left. It's very visual. 00:23:08.629 --> 00:23:11.842 We can typeset the diagram in ASCII art here. 00:23:11.843 --> 00:23:14.434 Then in this part here, 00:23:14.435 --> 00:23:18.273 we tell how the nodes are to be joined, 00:23:18.274 --> 00:23:22.880 which arrows have to have annotations, and so on. 23:22.880 --> 00:23:30.950 This language is extensible in the sense that 00:23:30.951 --> 00:23:37.280 here, comments that start 23:37.280 --> 00:23:42.690 with `%:` are interpreted as definitions 00:23:42.691 --> 00:23:44.819 for tree diagrams, 00:23:44.820 --> 00:23:49.394 lines that start with `%D` 00:23:49.395 --> 00:23:53.761 define 2D diagrams with arrows and stuff, 00:23:53.762 --> 00:23:57.683 and lines that start with command `%L` 00:23:57.684 --> 00:24:01.197 contain blocks of Lua code that we can use 00:24:01.198 --> 00:24:05.527 to extend the interpreter on the flag. 00:24:05.528 --> 00:24:09.746 Anyway, here are some recent examples 00:24:09.747 --> 00:24:16.146 of diagrams that I used Dednat6 to typeset. 00:24:16.147 --> 00:24:24.494 This diagram here was generated by this specification here, 00:24:24.495 --> 00:24:30.619 and this diagram here with the curved arrows 00:24:30.620 --> 00:24:36.200 was generated by this specification here. 24:36.200 --> 00:24:39.174 Dednat6 was very easy to extend. 00:24:39.175 --> 00:24:43.043 At some point I started to use it to generate diagrams 00:24:43.044 --> 00:24:46.067 using Pict2e, mainly for the classes 00:24:46.068 --> 00:24:49.673 that I give at the university, 00:24:49.674 --> 00:24:53.861 I teach mathematics in a place. 00:24:53.862 --> 00:24:58.979 Let me show an animation. Here is a diagram 00:24:58.980 --> 00:25:02.325 that I generated with Dednat6. 00:25:02.326 --> 00:25:05.385 It is a flipbook animation, 00:25:05.386 --> 00:25:08.253 we type page up and page down, 00:25:08.254 --> 00:25:10.783 and we go to the next page of the book 00:25:10.784 --> 00:25:13.248 and to the previous page of the book. 00:25:13.249 --> 00:25:16.924 Here is the source code that generates that. 00:25:16.925 --> 00:25:19.700 This source code is not very visual, 00:25:19.701 --> 00:25:21.800 so it's quite clumsy to edit 25:21.800 --> 25:28.280 a diagram directly in the TeX file like that. NOTE Manim 25:28.280 --> 00:25:33.437 These diagrams were inspired by something called Manim. 00:25:33.438 --> 00:25:36.713 I've forgotten the name of the guy, but it's a guy 00:25:36.714 --> 00:25:39.346 that makes many videos about mathematics, 00:25:39.347 --> 00:25:43.373 and he created this library called Manim 00:25:43.374 --> 00:25:46.417 for generating his animations. 00:25:46.418 --> 00:25:52.083 Other people adapted his library to make it more accessible. 00:25:52.084 --> 00:25:55.799 I tried to learn it, but each animation, 00:25:55.800 --> 00:25:59.191 even an animation with very few frames, 00:25:59.192 --> 00:26:03.770 each animation took ages to render, so it wasn't fun. 00:26:03.771 --> 00:26:08.345 Animations and PDFs can be rendered in seconds, 00:26:08.346 --> 00:26:11.160 so these things were fun for me 00:26:11.161 --> 00:26:17.440 because my laptop is very slow and Manim was not fun. 26:17.440 --> 00:26:24.263 Anyway, writing code like this inside a TeX file 00:26:24.264 --> 00:26:30.879 was not very fun because it was hard to debug. NOTE Generating diagrams from REPLs 00:26:30.880 --> 00:26:36.510 In 2022, I started to play with ways 00:26:36.511 --> 00:26:42.000 of generating these diagrams from REPLs 26:42.000 --> 00:26:46.309 and I found a way for Pict2e and a way for Tikz. 00:26:46.310 --> 00:26:49.520 Each one of these ways became a video. 26:49.520 --> 00:26:53.220 If you go to the list of first class videos of eev, 00:26:53.221 --> 00:26:55.088 you're going to see 00:26:55.089 --> 00:26:59.010 that there's a video about Pict2e here 00:26:59.011 --> 00:27:01.158 and a video about Tikz. 00:27:01.159 --> 00:27:04.187 Here you have some information 00:27:04.188 --> 00:27:07.508 like length and explanation, etc. 00:27:07.509 --> 00:27:11.513 Here are the pages for these videos. 00:27:11.514 --> 00:27:15.991 My page about the video about Pict2e is like this. 00:27:15.992 --> 00:27:20.800 It has some diagrams. This one is much nicer. 27:20.800 --> 00:27:26.605 A lot of people watched that video. I mean, 00:27:26.606 --> 00:27:31.080 I thought that 250 people watched it. 27:31.080 --> 00:27:35.344 For me, that's a million of people. 00:27:35.345 --> 00:27:40.402 This video is about how to extract diagrams 00:27:40.403 --> 00:27:46.512 from the Tikz manual, and how to run those examples in REPL 00:27:46.513 --> 00:27:52.936 and modify them bit by bit. This is a screenshot. 00:27:52.937 --> 00:27:57.432 Let me go back. At that point, 00:27:57.433 --> 00:28:01.800 these things were just prototypes, 28:01.800 --> 00:28:04.803 the code was not very nice, 00:28:04.804 --> 00:28:07.592 and in this year I wrote... 00:28:07.593 --> 00:28:12.123 I was able to unify those two ways of generating PDFs, 00:28:12.124 --> 00:28:15.665 the one for Tikz and the one for Pict2e. 00:28:15.666 --> 00:28:19.196 I unified them with many other things 00:28:19.197 --> 00:28:21.298 that generated diagrams. 00:28:21.299 --> 00:28:28.430 The basis of these things is something called Show2.lua. 00:28:28.431 --> 00:28:33.935 I'm not going to just show its details now, 00:28:33.936 --> 00:28:38.775 but it's an extension that generates Tikz code. 00:28:38.776 --> 00:28:43.305 It's just this. We can specify a diagram 00:28:43.306 --> 00:28:50.538 with just a block like this, and then if we run `show00`, 00:28:50.539 --> 00:28:53.694 it returns a string 00:28:53.695 --> 00:28:59.480 that is just the inner body of the TeX file. 28:59.480 --> 00:29:02.306 If we run this, we see the whole TeX file. 00:29:02.307 --> 00:29:05.200 If we run this we save the TeX file and 29:05.200 --> 00:29:09.196 we compile the TeX file to generate a PDF. 00:29:09.197 --> 00:29:12.557 If we run this, we show the PDF 00:29:12.558 --> 00:29:15.078 in the lower right window. 00:29:15.079 --> 00:29:20.026 That's the same thing for all my recent programs 00:29:20.027 --> 00:29:23.810 that generate PDFs. They are all integrated. 00:29:23.811 --> 00:29:28.267 Here is the basis for all my modules 00:29:28.268 --> 00:29:31.423 that generate diagrams with Pict2e. 00:29:31.424 --> 00:29:34.337 Its demos are not very interesting. 00:29:34.338 --> 00:29:38.556 Let me show some demos of extensions 00:29:38.557 --> 00:29:43.723 that do interesting things. This is a diagram 00:29:43.724 --> 00:29:47.901 that I created by editing it in a REPL, 00:29:47.902 --> 00:29:51.871 I create several Pict objects here. 00:29:51.872 --> 00:29:57.818 If I execute this, it compiles the object and 00:29:57.819 --> 00:30:04.523 generates a PDF. If I tap this, here is the PDF. 00:30:04.524 --> 00:30:10.919 If I just ask Lua to display what is pux here, 00:30:10.920 --> 00:30:17.435 it shows the source code in Pict2e of the diagram. 00:30:17.436 --> 00:30:20.932 The nice thing is that it is indented, 00:30:20.933 --> 00:30:24.348 so it's easy to debug the Pict2e code. 00:30:24.349 --> 00:30:28.504 If anyone is interested, the module that does the tricks 00:30:28.505 --> 00:30:31.947 for indentation is very easy to understand. 00:30:31.948 --> 00:30:34.920 it has lots of tests and test blocks, 00:30:34.921 --> 00:30:47.438 and I think that its data structures are easy to understand. 00:30:47.439 --> 00:30:57.904 Anyway, here is another example, the show is here. 00:30:57.905 --> 00:31:03.240 It generates a 3D diagram. NOTE Parsers 31:03.240 --> 00:31:05.897 Now let me talk about parsers 00:31:05.898 --> 00:31:08.997 and REPLs in a very strange place. 00:31:08.998 --> 00:31:15.148 I mean, using REPLs to build parsers step by step 00:31:15.149 --> 00:31:20.438 and replacing parts by more complex parts. 00:31:20.439 --> 00:31:24.492 I said that Lua is very minimalistic, 00:31:24.493 --> 00:31:26.964 and everybody knows that 00:31:26.965 --> 00:31:30.720 implementations of regular expressions 31:30.720 --> 00:31:33.973 are big and complex. So instead of coming 00:31:33.974 --> 00:31:36.375 with full regular expressions, 00:31:36.376 --> 00:31:41.320 Lua comes with something called patterns 00:31:41.321 --> 00:31:46.627 and a library function called string.match. 00:31:46.628 --> 00:31:50.820 Here is a copy of the part of the manual 00:31:50.821 --> 00:31:55.728 that explains a part of the syntax of patterns. 00:31:55.729 --> 00:32:00.090 Here's how string.match is described in the manual. 00:32:00.091 --> 00:32:04.536 It's just this: looks for the first match of pattern 00:32:04.537 --> 00:32:06.545 in the string s, blah blah blah. 00:32:06.546 --> 00:32:10.076 Then we have to go to the other section of the manual 00:32:10.077 --> 00:32:18.197 that explains patterns. Lua patterns are so simple, 00:32:18.198 --> 00:32:23.221 so limited, that they don't even have 00:32:23.222 --> 00:32:26.658 the alternation operator. 00:32:26.659 --> 00:32:33.135 Here is how it is described in the elisp manual, 00:32:33.136 --> 00:32:39.677 `\|` specifies an alternative, blah blah blah. 00:32:39.678 --> 00:32:45.880 When we want to build more complex regular expressions, 32:45.880 --> 00:32:48.365 patterns, grammars, etc., 00:32:48.366 --> 00:32:52.668 we have to use an external library for that. 00:32:52.669 --> 00:32:56.207 No, sorry, a library that is external, 00:32:56.208 --> 00:33:01.471 but that was written by one of the authors of Lua itself. 00:33:01.472 --> 00:33:03.943 This library is called Lpeg. 00:33:03.944 --> 00:33:06.330 Its manual says Lpeg is 00:33:06.331 --> 00:33:09.653 a new pattern matching library for Lua 00:33:09.654 --> 00:33:14.772 based on parsing expression grammars (PEGs). 00:33:14.773 --> 00:33:17.780 The manual is very terse. 00:33:17.781 --> 00:33:21.945 I found it incredibly hard to read. 00:33:21.946 --> 00:33:25.415 it doesn't have any diagrams. 00:33:25.416 --> 00:33:28.769 It has some examples, though. 00:33:28.770 --> 00:33:34.016 The Lua wiki has a big page called Lpeg Tutorial 00:33:34.017 --> 00:33:39.560 with lots of examples, but it also doesn't have diagrams. 33:39.560 --> 00:33:43.131 I found some things incredibly hard to understand. 00:33:43.132 --> 00:33:45.080 For example, this is something 33:45.080 --> 00:33:48.061 that is in the manual of Lpeg that I saw, 00:33:48.062 --> 00:33:51.480 and I thought, wow, great, this makes all sense 33:51.480 --> 00:33:53.946 and this is going to be very useful. 00:33:53.947 --> 00:33:57.280 It's a way to build grammars that can be recursive 33:57.280 --> 00:34:01.300 and they sort of can encode BNF grammars, 00:34:01.301 --> 00:34:05.128 we just have to translate the BNF a bit 00:34:05.129 --> 00:34:07.592 to get rid of some recursions 00:34:07.593 --> 00:34:10.959 and to translate them to something else. 00:34:10.960 --> 00:34:14.337 The manual also has some things that I thought, 00:34:14.338 --> 00:34:17.845 oh no, I don't have any idea of what this thing does. 00:34:17.846 --> 00:34:20.768 In fact, I saw these things for the first time 00:34:20.769 --> 00:34:27.294 more than 10 years ago, and they only started to make sense 00:34:27.295 --> 00:34:32.272 one year ago. One example is group captures. 00:34:32.273 --> 00:34:37.834 Lpeg also comes with a module called the re module. 00:34:37.835 --> 00:34:43.182 Let me pronounce it in Portuguese, the re module. 00:34:43.183 --> 00:34:45.741 Its manual says the re module 00:34:45.742 --> 00:34:49.503 provided by the file re.lua in the distribution 00:34:49.504 --> 00:34:56.757 supports some odd conventional regular expression syntax 00:34:56.758 --> 00:35:04.520 for pattern usage within lpeg. This is a quick reference. 35:04.520 --> 00:35:08.464 This thing is very brief. It has some nice examples, 00:35:08.465 --> 00:35:11.120 but it's hard to understand anyway. 35:11.120 --> 00:35:14.180 Here are some comments about 00:35:14.181 --> 00:35:18.631 my attempts to learn re.lua. This is a class. 00:35:18.632 --> 00:35:22.361 In this case, it's a very small class. 00:35:22.362 --> 00:35:26.091 This file implements a `pm` method. 00:35:26.092 --> 00:35:31.400 I'm going to show examples of other `pm` methods very soon. 00:35:31.401 --> 00:35:34.696 So this is a `pm` method for re.lua 00:35:34.697 --> 00:35:40.301 that lets us compare the syntax of lua patterns, lpeg, 00:35:40.302 --> 00:35:46.631 and re. See this example here. If we run this, 00:35:46.632 --> 00:35:51.379 it loads my version of lpeg, no sorry, 00:35:51.380 --> 00:35:56.013 my version of lpegrex. It shows that 00:35:56.014 --> 00:36:01.552 when we apply the `pm` method to this Lua pattern, 00:36:01.553 --> 00:36:05.960 this lpeg pattern, and this re pattern, 36:05.960 --> 00:36:08.238 they all give the same results. 00:36:08.239 --> 00:36:11.512 So we can use this kind of thing here to show 00:36:11.513 --> 00:36:15.588 how to translate from Lua patterns that are familiar 00:36:15.589 --> 00:36:19.280 because they are similar to regular expressions, 36:19.280 --> 00:36:25.251 only weaker, to lpeg that is super weird, 00:36:25.252 --> 00:36:30.084 and to re that is not so weird. 00:36:30.085 --> 00:36:35.425 Anyway, the comment says that in 2012, I had a project 00:36:35.426 --> 00:36:38.590 that needed a precedence parser 00:36:38.591 --> 00:36:42.277 that could parse arithmetical expressions 00:36:42.278 --> 00:36:46.314 with the right precedences. At that point 00:36:46.315 --> 00:36:49.031 I was still struggling with pure lpeg 00:36:49.032 --> 00:36:51.318 and I couldn't do much with it, 00:36:51.319 --> 00:36:54.576 so I tried to learn re.lua instead, 00:36:54.577 --> 00:36:59.291 and I wrote this old class here that allowed me to use 00:36:59.292 --> 00:37:01.755 a preprocessor on patterns for Lua. 00:37:01.756 --> 00:37:04.834 The thing is that with this preprocessor 00:37:04.835 --> 00:37:10.920 I could specify precedence grammars using this thing here 00:37:10.921 --> 00:37:14.488 that worked but was super clumsy, 00:37:14.489 --> 00:37:18.160 and I gave up after a few attempts. 37:18.160 --> 00:37:25.632 And in 2022 I heard about something called lpegrex 00:37:25.633 --> 00:37:30.760 that was a kind of extension of re, 37:30.760 --> 00:37:33.045 and it was much more powerful than re.lua, 00:37:33.046 --> 00:37:35.784 but after a while I realized that 00:37:35.785 --> 00:37:38.765 it had the same defects as re.lua. 00:37:38.766 --> 00:37:40.698 Let me explain that, 00:37:40.699 --> 00:37:43.920 because it has all to do with the things 37:43.920 --> 00:37:52.026 about black boxes and magic that I told in the beginning. 00:37:52.027 --> 00:37:59.046 Neither re.lua or lpegrex had some features that I needed. 00:37:59.047 --> 00:38:05.374 They received a pattern that was specified as a string 00:38:05.375 --> 00:38:08.868 and it converted that into an lpeg pattern, 00:38:08.869 --> 00:38:12.520 but it didn't let us explore the lpeg patterns 38:12.520 --> 00:38:14.529 that it generated. 00:38:14.530 --> 00:38:20.662 Their code was written in a way that was REPL-unfriendly. 00:38:20.663 --> 00:38:26.281 I couldn't modify parts of the code bit by bit in a REPL 00:38:26.282 --> 00:38:28.943 and try to change the code 00:38:28.944 --> 00:38:32.035 without changing the original file, say. 00:38:32.036 --> 00:38:35.353 The code was very hard to explore, to hack, 00:38:35.354 --> 00:38:38.238 and to extend in my opinion. 00:38:38.239 --> 00:38:42.018 The documentation was not very clear, 00:38:42.019 --> 00:38:45.600 and I sent wonderful messages to the 38:45.600 --> 00:38:51.013 developer of lpegrex, and he was too busy to help me. 00:38:51.014 --> 00:38:57.210 He answered very briefly. To be honest, I felt rejected. 00:38:57.211 --> 00:39:03.200 I felt that I wasn't doing anything interesting, whatever. NOTE ELpeg1.lua 39:03.200 --> 00:39:07.470 So in 2022, I was trying to learn lpegrex 00:39:07.471 --> 00:39:13.200 because I was thinking that it would solve my problems, 39:13.200 --> 00:39:16.666 but it didn't. It didn't have the features that I needed, 00:39:16.667 --> 00:39:18.400 and it was hard to extend and 39:18.400 --> 00:39:22.302 how to explore and hard to debug. 00:39:22.303 --> 00:39:28.960 I decided to rewrite it in a more hacker-friendly way, 39:28.960 --> 00:39:32.035 in the sense that it was modular 00:39:32.036 --> 00:39:37.160 and I could replace any part of the module from a REPL. 39:37.160 --> 00:39:42.640 My version of it was called ELpeg1.lua. 00:39:42.641 --> 00:39:48.120 I decided that in my version I wouldn't 39:48.120 --> 00:39:51.240 have the part that receives a grammar 00:39:51.241 --> 00:39:55.265 specified as a string and converts that to lpeg. 00:39:55.266 --> 00:39:58.984 I would just have the backend part 00:39:58.985 --> 00:40:02.171 that are the functions in lpeg 00:40:02.172 --> 00:40:06.320 that let us specify powerful grammars. 40:06.320 --> 00:40:15.161 Let me go back. Let me explain a bit about lpeg. 00:40:15.162 --> 00:40:20.780 Lua has coercions. The `+` expects to receive two numbers. 00:40:20.781 --> 00:40:25.930 If one of its arguments or both of them are strings, 00:40:25.931 --> 00:40:30.116 it converts the strings to numbers. 00:40:30.117 --> 00:40:37.091 So in this case here, `2 + "3"` returns the number 5. 00:40:37.092 --> 00:40:40.440 This is the concatenation operator. 00:40:40.441 --> 00:40:44.960 It expects to receive strings. In this case, it will 40:44.960 --> 00:40:47.541 convert the number 2 to the string "2" 00:40:47.542 --> 00:40:50.960 and the concatenation of these two things will be 40:50.960 --> 00:40:55.917 "23". Oops, sorry, "23" as a string. 00:40:55.918 --> 00:41:04.480 lpeg also has some coercions. I usually set these globals 41:04.480 --> 00:41:10.013 to let me write my grammars in a very compact way. 00:41:10.014 --> 00:41:13.811 So instead of lpeg.B, lpeg.C, etc. 00:41:13.812 --> 00:41:17.878 I use globals like B, C, and so on. 00:41:17.879 --> 00:41:21.720 And with these globals I can write 41:21.720 --> 00:41:36.047 things like this, `C(1) * "_"`. And lpeg knows that lpeg.C, 00:41:36.048 --> 00:41:41.147 sorry, it sort of expands these to lpeg.C, 00:41:41.148 --> 00:41:43.590 but lpeg.C expects to receive an lpeg pattern 00:41:43.591 --> 00:41:48.547 and 1 is not yet an lpeg pattern. 00:41:48.548 --> 00:41:53.347 So it is coerced into an lpeg pattern by calling lpeg.P. 00:41:53.348 --> 00:42:02.481 So this short thing here becomes equivalent to 00:42:02.482 --> 00:42:07.200 `lpeg.C(lpeg.P(1))`. And the multiplication when at least one of 42:07.200 --> 42:13.320 its arguments is an lpeg pattern, it expects to receive two lpeg patterns. And in this 42:13.320 --> 42:19.200 case the one at the right is just a string, so it is coerced to an lpeg pattern by using 42:19.200 --> 42:29.360 lpeg.P. With this idea we can sort of understand this comparison here. I mean, let me run it 42:29.360 --> 42:37.440 again. This first part is very similar to a regular expression here at the left. And 42:37.440 --> 42:51.440 when we apply this lpeg, sorry, this lua pattern to this subject here, the result is this thing 42:51.440 --> 42:56.040 here, this thing, this thing and this thing. I'm going to call each one of these results 42:56.040 --> 43:04.080 captures. So each of these things between parentheses captures a substring of the original 43:04.080 --> 43:11.520 string and these captured substrings are returned in a certain order. Here is how to express 43:11.520 --> 43:20.720 the same thing in lpeg. It's very cryptic, but it's a good way to understand some basic 43:20.720 --> 43:29.880 operators of lpeg. I mean, we can look at the menu and understand what C, S and R do 43:29.880 --> 43:41.360 and also exponentiation. And this strange thing here receives this string here, runs 43:41.360 --> 43:46.760 a function that I have defined that converts it to an object of a certain class and that 43:46.760 --> 43:55.240 class represents re patterns. So this thing is treated as a pattern for re.lua and it 43:55.240 --> 44:04.040 is matched again the string and it returns the same thing as the other one. Also this 44:04.040 --> 44:10.680 thing here also has a comparison with lpeg.rex, but these patterns are very, very trivial. 44:10.680 --> 44:17.340 They don't do anything very strange. So let's go back and see what kinds of very strange 44:17.340 --> 44:31.480 things there are. Here is the page of lpeg.rex at GitHub. Here is the documentation. It's 44:31.480 --> 44:39.120 relatively brief. It explains lpeg.rex as being an extension of re.lua. So 44:39.120 --> 44:44.880 it explains mainly the additional features. Here is a quick reference that explains only 44:44.880 --> 44:56.840 the additional features. Some of these things I was able to understand by struggling a lot, 44:56.840 --> 45:08.720 and some I wasn't able to even by spending several evenings trying to build examples. 45:08.720 --> 45:16.600 This is something very nice. lpeg.rex comes with some example parsers. Here is 45:16.600 --> 45:25.720 a parser that parses the lua grammar. I mean, this is the grammar for lua 5.4 at the end 45:25.720 --> 45:35.080 of the reference manual. It's just this. And this is a kind of BNF, and this is the BNF 45:35.080 --> 45:43.840 translated to the language of lpeg.rex. This thing uses many constructions that are 45:43.840 --> 45:51.840 in re.lua and some extra constructions that are described here. With these examples, 45:51.840 --> 46:00.280 I was able to understand some of these things here that are described here in the quick 46:00.280 --> 46:13.840 reference, but not all. So I wasn't able to use lpeg.rex by itself because some things 46:13.840 --> 46:21.560 didn't make much sense. I decided to re implement it in my own style because that 46:21.560 --> 46:29.120 would be a way to map... at the very least, map what I understood and what I didn't and 46:29.120 --> 46:38.160 learn one feature at a time, do comparisons and so on. Here I pointed to two features 46:38.160 --> 46:44.880 of lpeg. One I said, oh great, this thing can be used to define grammars, even recursive 46:44.880 --> 46:52.260 grammars and so on. And this is an "oh no" feature. One thing that didn't make any sense at all: 46:52.260 --> 47:01.760 group captures. One thing that I did to understand group captures was to represent them as diagrams. 47:01.760 --> 47:08.200 Of course in the beginning I was drawing these diagrams by hand, but then I realized that 47:08.200 --> 47:16.680 I could use the bits of lpeg that I already knew to build a grammar that would parse a 47:16.680 --> 47:24.400 little language and generate these diagrams in LaTeX. I was able to make this. In 47:24.400 --> 47:35.520 this diagram here, this thing above the arrow is a piece of Lua code that specifies an lpeg 47:35.520 --> 47:43.160 pattern. This thing here at the top is the string that is being matched and the things 47:43.160 --> 47:57.880 below the under braces are the captures that each thing captures. For example, this under 47:57.880 --> 48:03.520 brace here corresponds to this pattern here that parses a single character but doesn't 48:03.520 --> 48:10.680 return any captures. This thing here parses a single B and doesn't return any captures. 48:10.680 --> 48:17.800 This thing here parses a single character and captures it. And this thing here parses 48:17.800 --> 48:24.920 the character D and captures it. And this other thing here that transforms this pattern 48:24.920 --> 48:35.040 into another pattern returns first a capture with all the string that was parsed by this 48:35.040 --> 48:44.000 pattern here and then all the captures returned by this thing here before the column. So this 48:44.000 --> 48:51.840 was a way to build concrete examples for things that the lpeg manual was explaining in a very 48:51.840 --> 48:58.600 terse way and it worked for me. Some things that were very mysterious started to make 48:58.600 --> 49:10.200 sense and I started to have intelligent questions to ask in the mailing list. With that 49:10.200 --> 49:22.040 I was able to understand what are group captures that receive a name. Well, let me explain 49:22.040 --> 49:30.400 what this does. This thing here parses the empty string and returns this as a constant. 49:30.400 --> 49:38.520 So this is something that doesn't exist in regular expressions. It parses nothing and 49:38.520 --> 49:46.800 returns this as a capture. Then this thing here returns two constants here and parses 49:46.800 --> 49:54.440 the empty string. And this thing here, D, converts the results of this thing here into 49:54.440 --> 50:04.160 a group capture and stores it in the label D. And then here's another constant capture. NOTE Building lists 50:04.160 --> 50:15.560 I realized that these things here were similar to how Lua specifies building lists. 50:15.560 --> 50:22.320 When we build a table and we say that the first element of the table is here, this element 50:22.320 --> 50:30.600 is put at the end of the table. After that we say D equals to say 42. We are putting 50:30.600 --> 50:39.880 the 42 in the slot whose key is D. This was happening with lpeg captures but there was 50:39.880 --> 50:49.320 something very strange. These group captures could hold more than one capture, more than 50:49.320 --> 50:57.400 one value. So there was something between lists and tables. I started to use this notation 50:57.400 --> 51:09.840 to explain in my notation what they were doing. Many things started to make sense, many mysterious 51:09.840 --> 51:20.480 sentences in the manual started to make sense but some didn't. But at least I was able to 51:20.480 --> 51:26.960 send some intelligent questions to the mailing list and the author of Lua and LPEG answered 51:26.960 --> 51:35.920 some of them. He was not very happy about my questions. He told me that those diagrams 51:35.920 --> 51:47.280 were a waste of time, the manual was perfectly clear and so on, whatever. So it was weird, 51:47.280 --> 51:56.440 but I was able to understand lots of things from his answers. So this is a copy of one 51:56.440 --> 52:02.040 of my messages, then there's another one, another one, some of the diagrams. Then he 52:02.040 --> 52:10.080 complained about these diagrams, he said that these things here that look like table constructions 52:10.080 --> 52:22.720 do not exist, whatever. Anyway, once I understood group captures, many features were very easy 52:22.720 --> 52:30.800 to understand and I started to be able to use lpeg to build some very interesting things. 52:30.800 --> 52:39.600 I was able to reproduce some of the features that I saw in lpegrex. Remember that this 52:39.600 --> 52:53.400 is a syntax of Lua. Here I was able to understand how these things here were translated to lpeg 52:53.400 --> 53:02.880 code, to lpeg patterns by using group captures in a certain way. I was able to implement 53:02.880 --> 53:13.080 them in ELpeg1.lua. after some time I was able to use ELpeg1.lua to build grammars that 53:13.080 --> 53:21.080 were able to parse arithmetical expressions with the right precedence. here's an example 53:21.080 --> 53:26.920 in which I built the grammar step by step and I test the current grammar and I replace 53:26.920 --> 53:34.400 a bit and then I test the new grammar and so on. You can see that the result is 53:34.400 --> 53:48.720 always a tree that is drawn in a nice two dimensional way. At this point, these powers 53:48.720 --> 53:57.760 here are returned as a list, as an operation power with several arguments here and then 53:57.760 --> 54:05.560 I apply a kind of parsing combinator here that transforms these trees into other trees 54:05.560 --> 54:14.200 and with these combinators here I can specify that the power is associative in a certain 54:14.200 --> 54:22.320 direction, the division is associative in another direction, the minus uses the same 54:22.320 --> 54:29.520 direction as a division and so on and they have the right precedences. So here are the 54:29.520 --> 54:42.360 tests. So here's my file ELpeg.lua, it has several classes. Each class has tests after 54:42.360 --> 54:52.040 it. I was able to implement something that lpeg.rex has that's called keywords, that's 54:52.040 --> 54:59.160 very useful for parsing problems in programming languages. I was able to implement something 54:59.160 --> 55:10.640 similar to the debugger, to the pack debugger that lpeg uses, but I was frustrated by some 55:10.640 --> 55:23.280 limitations of the debugger and I implemented my own that is much better and let me show 55:23.280 --> 55:33.800 something else. I was able to translate a good part of the Lua parser here to lpeg1.lua. 55:33.800 --> 55:45.880 I haven't finished yet but I have most of the translation here and after having all 55:45.880 --> 55:54.960 that I was able to build other grammars very quickly. Writing new parsers finally became 55:54.960 --> 56:08.560 fun and here's one example that I showed in the beginning. If I remember correctly, I 56:08.560 --> 56:15.680 took a figure from the Wikipedia, I don't have its link now, but I specify a grammar 56:15.680 --> 56:24.280 that parses exactly the example that appears in the Wikipedia. So with my grammar, considering 56:24.280 --> 56:36.680 that the top level entry is statement, when I parse this string here, the result is this 56:36.680 --> 56:44.840 tree and I can do some operations on that. I can define how this thing is to be converted 56:44.840 --> 56:53.400 into LaTeX. I can define other operations that convert trees into other trees and here's 56:53.400 --> 57:01.760 some tests of these operations. This is what I showed in the beginning. I'm not going to 57:01.760 --> 57:10.480 explain all the details of this thing now. This show converts this thing into LaTeX in 57:10.480 --> 57:39.320 the way specified by these instructions here. And here's the result, the LaTeX result. 57:39.320 --> 57:46.880 These diagrams here are generated by this file here that defines a simple grammar that 57:46.880 --> 57:56.720 parses this thing here and then LaTeX it in a certain way and also tests to check if this 57:56.720 --> 58:06.600 code here that is Lua code that generates an lpeg grammar, parses this subject here, and 58:06.600 --> 58:16.880 returns the expected result. So this is the code that I wanted to show. I wanted to show 58:16.880 --> 58:23.920 many more things, but I wasn't able to prepare them before the conference. And I hope that 58:23.920 --> 58:33.240 soon, for some value of soon, I'll be able to create REPL based tutorials for LPG, G and 58:33.240 --> 58:42.080 ELpeg1.Lua where Lpeg is something very famous. Here is a module of LPG. I could also do something 58:42.080 --> 58:55.600 like this for ELpeg, and ELpeg1.lua is the thing that I wrote, the one that has tests in comments 58:55.600 --> 59:04.920 and the tests usually generate trees and sometimes they generate tag code. So that's it, I wanted 59:04.920 --> 59:26.040 to present much more, but I wasn't able to prepare it. So sorry, thanks, bye!