diff options
Diffstat (limited to '2023/captions/emacsconf-2023-repl--repls-in-strange-places-lua-latex-lpeg-lpegrex-tikz--eduardo-ochs--main.vtt')
| -rw-r--r-- | 2023/captions/emacsconf-2023-repl--repls-in-strange-places-lua-latex-lpeg-lpegrex-tikz--eduardo-ochs--main.vtt | 3324 |
1 files changed, 3324 insertions, 0 deletions
diff --git a/2023/captions/emacsconf-2023-repl--repls-in-strange-places-lua-latex-lpeg-lpegrex-tikz--eduardo-ochs--main.vtt b/2023/captions/emacsconf-2023-repl--repls-in-strange-places-lua-latex-lpeg-lpegrex-tikz--eduardo-ochs--main.vtt new file mode 100644 index 00000000..723fc45a --- /dev/null +++ b/2023/captions/emacsconf-2023-repl--repls-in-strange-places-lua-latex-lpeg-lpegrex-tikz--eduardo-ochs--main.vtt @@ -0,0 +1,3324 @@ +WEBVTT captioned by eduardo +Kind: captions +Language: en-GB + +NOTE Intro + +00:00:00.000 --> 00:00:03.079 +Hi! My name is Eduardo Ochs + +00:00:03.080 --> 00:00:05.519 +and the title of this talk is: REPLs + +00:00:05.520 --> 00:00:09.399 +in strange places - Lua, LateX, LPeg, LPegRex, + +00:00:09.400 --> 00:00:12.119 +and TikZ. I'm the author of an Emacs + +00:00:12.120 --> 00:00:14.879 +package called eev, and this is a talk + +00:00:14.880 --> 00:00:18.479 +at the EmacsConf 2023, that is happening in + +00:00:18.480 --> 00:00:22.519 +December 2023, at the internets. + +NOTE Diagrams + +00:00:22.520 --> 00:00:23.079 +This is one of the + +00:00:23.080 --> 00:00:24.919 +examples of diagrams that we are + +00:00:24.920 --> 00:00:27.639 +going to see - let me show how I generate + +00:00:27.640 --> 00:00:30.599 +it... one second, + +00:00:30.600 --> 00:00:35.799 +I have to use a smaller font here... + +00:00:35.800 --> 00:00:39.159 +this is a file called ParseTree2.lua... + +00:00:39.160 --> 00:00:42.919 +let me go back to this block of tests again... + +00:00:42.920 --> 00:00:43.879 +and now if I run + +00:00:43.880 --> 00:00:47.759 +this... + +00:00:47.760 --> 00:00:50.159 +we get these outputs here at the + +00:00:50.160 --> 00:00:53.959 +right, and then in this line here it + +00:00:53.960 --> 00:00:58.119 +generates a PDF, and if I type f8 here it + +00:00:58.120 --> 00:01:03.919 +shows the PDF in the lower right window. + +NOTE eev + +00:01:03.920 --> 00:01:06.079 +Let me start by explaining + +00:01:06.080 --> 00:01:09.839 +briefly what is eev. + +00:01:09.840 --> 00:01:12.239 +First: it is something that + +00:01:12.240 --> 00:01:14.759 +appeared by accident in the mid-90s - I + +00:01:14.760 --> 00:01:16.799 +explained this story in my + +00:01:16.800 --> 00:01:20.159 +presentation at the EmacsConf 2019... + +00:01:20.160 --> 00:01:23.159 +it's a package... it's an Emacs + +00:01:23.160 --> 00:01:26.519 +package that is part of ELPA... it has at + +00:01:26.520 --> 00:01:29.679 +least 10 users - those are the ones + +00:01:29.680 --> 00:01:32.559 +that I know by name... + +00:01:32.560 --> 00:01:38.439 +eev means `emacs-execute-verbosely'... + +00:01:38.440 --> 00:01:40.959 +eev is something that treats eval-last-sexp + +00:01:40.960 --> 00:01:43.999 +as the central feature of Emacs... + +00:01:44.000 --> 00:01:45.599 +eev blurs the distinction between + +00:01:45.600 --> 00:01:48.919 +programmers and users, and it replaces + +00:01:48.920 --> 00:01:51.679 +the slogan "users should not be forced to + +00:01:51.680 --> 00:01:53.679 +see Lisp", that is something that Richard + +00:01:53.680 --> 00:01:57.559 +Stallman told me once, by "users should see + +00:01:57.560 --> 00:02:00.479 +Lisp instead of buttons" and "new users + +00:02:00.480 --> 00:02:03.999 +should see Lisp in the first 5 minutes"... + +00:02:04.000 --> 00:02:05.279 +I'm going to show + +00:02:05.280 --> 00:02:08.959 +some examples of that soon. + +00:02:08.960 --> 00:02:11.959 +Eev uses code in comments a lot, + +00:02:11.960 --> 00:02:15.119 +and also tests in comments... + +00:02:15.120 --> 00:02:17.679 +I changed my way of presenting it + +00:02:17.680 --> 00:02:19.679 +and it became very REPL-centric + +00:02:19.680 --> 00:02:22.319 +in the last few years, in the + +00:02:22.320 --> 00:02:24.399 +sense that I start by explaining its + +00:02:24.400 --> 00:02:28.679 +main features by its support for REPLs... + +00:02:28.680 --> 00:02:31.079 +eev supposes + +00:02:31.080 --> 00:02:32.639 +that we want to keep + +00:02:32.640 --> 00:02:35.199 +executable notes of everything - I'm also + +00:02:35.200 --> 00:02:37.159 +going to show examples of this in a + +00:02:37.160 --> 00:02:40.479 +second... eev has lots of "videos for + +00:02:40.480 --> 00:02:43.559 +people who hate videos", and it tries to + +00:02:43.560 --> 00:02:46.159 +do everything with very little magic and + +00:02:46.160 --> 00:02:48.839 +without black boxes - I'm going to explain + +00:02:48.840 --> 00:02:50.319 +many of these things very soon. + +NOTE Another figure + +00:02:50.320 --> 00:02:52.799 +This is a figure that that I'm going + +00:02:52.800 --> 00:02:57.119 +to show in details soon, that is + +00:02:57.120 --> 00:02:59.959 +about something important about Lua... + +00:02:59.960 --> 00:03:03.959 +the font is very bad now, so let me + +00:03:03.960 --> 00:03:07.559 +change the font... the figure is this one... + +00:03:07.560 --> 00:03:08.239 +and... + +00:03:08.240 --> 00:03:12.519 +what most people do when they + +00:03:12.520 --> 00:03:14.479 +visit a file with something + +00:03:14.480 --> 00:03:16.479 +interesting on it is that they just go + +00:03:16.480 --> 00:03:18.679 +there and they set a bookmark there, or + +00:03:18.680 --> 00:03:21.959 +they put the position in a register... + +00:03:21.960 --> 00:03:26.959 +but I prefer to keep + +00:03:26.960 --> 00:03:29.199 +links to everything that is interesting + +00:03:29.200 --> 00:03:32.119 +as elisp hyperlinks. So, for example, this is + +00:03:32.120 --> 00:03:35.079 +an elisp hyperlink to a file, that goes + +00:03:35.080 --> 00:03:37.599 +to this anchor here, and to this string + +00:03:37.600 --> 00:03:41.439 +after this anchor... this is a variant + +00:03:41.440 --> 00:03:44.239 +that opens that file in the window + +00:03:44.240 --> 00:03:45.479 +at the right - + +00:03:45.480 --> 00:03:48.879 +here... and this is + +00:03:48.880 --> 00:03:53.279 +a sexp that changes the font. I + +00:03:53.280 --> 00:03:56.679 +have a command with a very short name + +00:03:56.680 --> 00:03:59.439 +that does that, but I + +00:03:59.440 --> 00:04:02.959 +prefer to keep that as a one-liner. + +00:04:02.960 --> 00:04:06.919 +About the videos... we can see + +00:04:06.920 --> 00:04:10.079 +the list of first-class videos of eev + +00:04:10.080 --> 00:04:14.759 +by executing this, M-x find-1stclassvideos, + +00:04:14.760 --> 00:04:18.639 +or by running this alias here, M-x 1c... + +00:04:18.640 --> 00:04:20.679 +and then what we see is this... + +00:04:20.680 --> 00:04:24.239 +the first sexp here + +00:04:24.240 --> 00:04:26.959 +regenerates this buffer - so we can make a + +00:04:26.960 --> 00:04:29.399 +mess here and then run this and the + +00:04:29.400 --> 00:04:33.519 +original buffer is regenerated again in + +00:04:33.520 --> 00:04:34.959 +a clean way... + +00:04:34.960 --> 00:04:36.919 +each of these things here + +00:04:36.920 --> 00:04:40.879 +opens a buffer with information about + +00:04:40.880 --> 00:04:43.999 +a video... let me take a specific + +00:04:44.000 --> 00:04:49.159 +example here... this video here is about + +00:04:49.160 --> 00:04:51.039 +one of the ancestors of this talk, that + +00:04:51.040 --> 00:04:53.479 +is a library that I wrote + +00:04:53.480 --> 00:04:58.479 +for creating diagrams in LaTeX using + +00:04:58.480 --> 00:05:03.519 +a package called Pict2e using REPLs... + +00:05:03.520 --> 00:05:03.959 +anyway... + +00:05:03.960 --> 00:05:06.599 +the thing is that if we + +00:05:06.600 --> 00:05:11.599 +run a sexp like this one and we don't + +00:05:11.600 --> 00:05:14.679 +have a local copy of the video eev + +00:05:14.680 --> 00:05:17.599 +will try to download to the local copy - + +00:05:17.600 --> 00:05:20.119 +and instead of doing that by asking + +00:05:20.120 --> 00:05:21.719 +something like "do you want me + +00:05:21.720 --> 00:05:23.999 +to download the local copy? Blah + +00:05:24.000 --> 00:05:27.999 +blah blah blah blah..." it simply opens a + +00:05:28.000 --> 00:05:30.719 +buffer like this, I mean, if we don't + +00:05:30.720 --> 00:05:33.359 +have a local copy yet it will open a + +00:05:33.360 --> 00:05:36.359 +buffer like this one, in which these + +00:05:36.360 --> 00:05:39.199 +things here in comments are links to the + +00:05:39.200 --> 00:05:43.839 +documentation... I mean, this thing here + +00:05:43.840 --> 00:05:46.159 +explains the idea of local copies + +00:05:46.160 --> 00:05:48.759 +of files from the internet... + +00:05:48.760 --> 00:05:54.759 +there are more details here, and here... + +00:05:54.760 --> 00:05:57.159 +and this is a script that we + +00:05:57.160 --> 00:06:00.519 +can execute line by line, so instead of + +00:06:00.520 --> 00:06:02.359 +this script being hidden behind the + +00:06:02.360 --> 00:06:06.119 +button that we just press after a + +00:06:06.120 --> 00:06:08.399 +question like "Do you want me to do + +00:06:08.400 --> 00:06:10.239 +something blah blah blah? Yes or no?" + +00:06:10.240 --> 00:06:13.639 +the script is visible here and we can + +00:06:13.640 --> 00:06:17.599 +execute it step by step... it creates a + +00:06:17.600 --> 00:06:20.799 +terminal with a shell here in the + +00:06:20.800 --> 00:06:24.799 +right window, and when we type f8 in + +00:06:24.800 --> 00:06:26.839 +one of these lines here the lines are + +00:06:26.840 --> 00:06:29.119 +sent... (...) so this is going + +00:06:29.120 --> 00:06:31.759 +to download a copy of the video... the + +00:06:31.760 --> 00:06:36.639 +wget says that I already have a copy of + +00:06:36.640 --> 00:06:39.479 +the video and its subtitles... and so on. + +00:06:39.480 --> 00:06:43.879 +And after getting a copy of the video + +00:06:43.880 --> 00:06:48.159 +we can run this sexp here and it displays + +00:06:48.160 --> 00:06:49.919 +the video. + +00:06:49.920 --> 00:06:55.399 +I said that eev has lots of + +00:06:55.400 --> 00:06:58.399 +"videos for people who hate videos", and + +00:06:58.400 --> 00:06:59.679 +the idea is that very few + +00:06:59.680 --> 00:07:02.039 +people are going to watch the videos in + +00:07:02.040 --> 00:07:06.559 +real time... and most of the people that + +00:07:06.560 --> 00:07:08.279 +I know - or: most of the people that + +00:07:08.280 --> 00:07:10.639 +are interested in eev in some + +00:07:10.640 --> 00:07:13.479 +way... they are going to watch just + +00:07:13.480 --> 00:07:16.319 +small sections of the video, and most of + +00:07:16.320 --> 00:07:17.559 +the time they're just going to read the + +00:07:17.560 --> 00:07:20.799 +subtitles of the video. So, for each + +00:07:20.800 --> 00:07:23.479 +one of the videos we have a page + +00:07:23.480 --> 00:07:27.039 +about the video... let me see if I + +00:07:27.040 --> 00:07:29.999 +have internet here... yes. This is a + +00:07:30.000 --> 00:07:32.879 +page... + +00:07:32.880 --> 00:07:38.999 +and usually these pages have a link + +00:07:39.000 --> 00:07:40.759 +to another page that + +00:07:40.760 --> 00:07:43.239 +has all the subtitles of the + +00:07:43.240 --> 00:07:46.639 +video... uh, wherever... in this one + +00:07:46.640 --> 00:07:48.319 +it's not so visible... + +00:07:48.320 --> 00:07:50.599 +but anyway, there are several + +00:07:50.600 --> 00:07:52.479 +ways of accessing the subtitles of the + +00:07:52.480 --> 00:07:56.239 +video, and one of the ways is by running + +00:07:56.240 --> 00:07:57.519 +this sexp here, + +00:07:57.520 --> 00:08:01.559 +that opens a file in Lua that is + +00:08:01.560 --> 00:08:03.319 +what I use to generate the + +00:08:03.320 --> 00:08:04.479 +subtitles. + +00:08:04.480 --> 00:08:08.519 +Anyway... by the way, these things... each + +00:08:08.520 --> 00:08:12.039 +one of these things here is a hyperlink + +00:08:12.040 --> 00:08:15.239 +to a position of the video, so if I type + +00:08:15.240 --> 00:08:18.879 +this the right way it goes to that + +00:08:18.880 --> 00:08:24.119 +position. Anyway, let me go back... + +00:08:24.120 --> 00:08:27.279 +also, the tutorials of eev... the + +00:08:27.280 --> 00:08:31.359 +"intros" of eev, that start with "find-" and + +00:08:31.360 --> 00:08:34.279 +end with "-intro", they have lots of blocks + +00:08:34.280 --> 00:08:39.039 +that say "[Video links:]", like this one, and + +00:08:39.040 --> 00:08:41.359 +these blocks have links to positions + +00:08:41.360 --> 00:08:43.879 +in videos, and if we don't have a local + +00:08:43.880 --> 00:08:47.919 +copy of the video yet the thing shows + +00:08:47.920 --> 00:08:49.799 +us a script that lets us download the + +00:08:49.800 --> 00:08:50.599 +local copy. + +00:08:50.600 --> 00:08:54.399 +Anyway, I said that I was going + +00:08:54.400 --> 00:08:58.759 +to explain what I mean by "magic" and + +00:08:58.760 --> 00:08:59.639 +"black boxes". + +00:08:59.640 --> 00:09:03.119 +this is something that I've been + +00:09:03.120 --> 00:09:05.119 +trying to explain for a long time, and I + +00:09:05.120 --> 00:09:07.319 +think that I got a very good explanation + +00:09:07.320 --> 00:09:09.839 +about that in a video that I made + +00:09:09.840 --> 00:09:13.199 +about something called eev-wconfig, that + +00:09:13.200 --> 00:09:14.999 +is a tool for configuring eev on + +00:09:15.000 --> 00:09:19.199 +Windows without "magic" - without buttons + +00:09:19.200 --> 00:09:22.479 +that do things without explaining what + +00:09:22.480 --> 00:09:22.879 +they're doing. + +00:09:22.880 --> 00:09:25.799 +This is a part of the subtitles + +00:09:25.800 --> 00:09:28.039 +of the video, let me read that... + +00:09:28.040 --> 00:09:32.319 +eev-wconfig is an attempt to solve the + +00:09:32.320 --> 00:09:35.039 +problem of how to install these things + +00:09:35.040 --> 00:09:37.279 +on Windows both without magic and with + +00:09:37.280 --> 00:09:37.879 +very little + +00:09:37.880 --> 00:09:41.679 +magic. Remember this slogan: "any + +00:09:41.680 --> 00:09:44.359 +sufficiently advanced technology is + +00:09:44.360 --> 00:09:45.399 +indistinguishable from + +00:09:45.400 --> 00:09:49.679 +magic". Here in this video I'm going to + +00:09:49.680 --> 00:09:52.199 +use the term magic as a shorthand + +00:09:52.200 --> 00:09:55.239 +for sufficiently advanced technology, + +00:09:55.240 --> 00:09:57.799 +that is something that is complex and + +00:09:57.800 --> 00:10:00.199 +non-obvious and that is + +00:10:00.200 --> 00:10:02.119 +indistinguishable from magic in the + +00:10:02.120 --> 00:10:04.119 +sense of being almost impossible to + +00:10:04.120 --> 00:10:07.439 +understand. And I'm also going to use a + +00:10:07.440 --> 00:10:10.279 +the term "black box" as a near-synonym for + +00:10:10.280 --> 00:10:13.079 +magic, and sometimes the term + +00:10:13.080 --> 00:10:16.039 +"black box" is more convenient even though + +00:10:16.040 --> 00:10:17.919 +it's a bit longer - it has more + +00:10:17.920 --> 00:10:20.159 +letters - because when I use the term + +00:10:20.160 --> 00:10:22.599 +black box it invites us to use + +00:10:22.600 --> 00:10:25.479 +expressions like "opening the black box", + +00:10:25.480 --> 00:10:26.639 +and I'm going to use that + +00:10:26.640 --> 00:10:28.039 +expression a lot. + +00:10:28.040 --> 00:10:37.399 +Now let me try to explain what is... + +00:10:37.400 --> 00:10:41.039 +sorry, let me change the font... + +00:10:41.040 --> 00:10:45.479 +what is Lua. Lua is a minimalistic + +00:10:45.480 --> 00:10:49.999 +language, in the sense of + +00:10:50.000 --> 00:10:53.679 +"batteries not included"... it uses + +00:10:53.680 --> 00:10:55.999 +associative tables for most of its data + +00:10:56.000 --> 00:10:56.799 +structures... + +00:10:56.800 --> 00:11:00.239 +and it is so minimalistic + +00:11:00.240 --> 00:11:03.999 +that its default print function, when + +00:11:04.000 --> 00:11:06.679 +we tell... when we create an associative + +00:11:06.680 --> 00:11:09.559 +table and we ask it to print... + +00:11:09.560 --> 00:11:13.319 +when we ask "print" to print an + +00:11:13.320 --> 00:11:15.719 +associative table it just prints the + +00:11:15.720 --> 00:11:17.879 +address of the table. Here are some + +00:11:17.880 --> 00:11:21.599 +examples... here is a table, and when we + +00:11:21.600 --> 00:11:24.679 +ask "print" to print it it just says + +00:11:24.680 --> 00:11:26.839 +that it's the table at this address here. + +00:11:26.840 --> 00:11:30.119 +So, one of things that that most + +00:11:30.120 --> 00:11:32.919 +people do when they start using Lua is + +00:11:32.920 --> 00:11:35.239 +that either they download a package with + +00:11:35.240 --> 00:11:37.079 +a pretty-printing function or they write + +00:11:37.080 --> 00:11:39.359 +their own pretty-printing functions. My + +00:11:39.360 --> 00:11:41.519 +own pretty-printing function is called + +00:11:41.520 --> 00:11:46.159 +PP, with upper case letters, and it works + +00:11:46.160 --> 00:11:47.679 +like this... + +00:11:47.680 --> 00:11:50.279 +and it prints associative tables + +00:11:50.280 --> 00:11:53.839 +in a way like this. It says that for + +00:11:53.840 --> 00:11:57.479 +the key 1 the the value associated to + +00:11:57.480 --> 00:12:00.039 +it is 2, for the key 2 the value is + +00:12:00.040 --> 00:12:04.959 +3, and for the key 3 the value is 5. + +00:12:04.960 --> 00:12:11.079 +When I started using Lua one of my + +00:12:11.080 --> 00:12:13.839 +favorite languages was also a language + +00:12:13.840 --> 00:12:15.639 +that used associative tables a lot - + +00:12:15.640 --> 00:12:16.839 +it was called Icon... + +00:12:16.840 --> 00:12:21.039 +and I had to write my own + +00:12:21.040 --> 00:12:23.839 +pretty-printing functions for Icon, so + +00:12:23.840 --> 00:12:27.319 +I just had to port my pretty-printing + +00:12:27.320 --> 00:12:29.719 +functions to Lua... and my first + +00:12:29.720 --> 00:12:32.239 +version looked at something like this... it + +00:12:32.240 --> 00:12:35.999 +just had some some global functions... lots + +00:12:36.000 --> 00:12:39.639 +of them, actually... + +00:12:39.640 --> 00:12:42.279 +and after a while I rewrote it, and I + +00:12:42.280 --> 00:12:44.599 +rewrote it again, and again, and again, and + +00:12:44.600 --> 00:12:47.279 +this is one of the versions of that, + +00:12:47.280 --> 00:12:49.879 +is not even the default at this + +00:12:49.880 --> 00:12:51.559 +point... + +00:12:51.560 --> 00:12:54.119 +"Tos" is for "to string"... + +00:12:54.120 --> 00:12:58.279 +and this is a demo... + +00:12:58.280 --> 00:13:01.919 +it's very modular, so it's easy to replace + +00:13:01.920 --> 00:13:05.639 +parts of it, or to toggle flags... and this + +00:13:05.640 --> 00:13:08.119 +is an example. If I try to print the + +00:13:08.120 --> 00:13:09.999 +table of methods for a certain + +00:13:10.000 --> 00:13:14.359 +class... I will need a smaller font... + +00:13:14.360 --> 00:13:16.799 +it prints the table like this, with the + +00:13:16.800 --> 00:13:20.039 +names of the methods and then links to + +00:13:20.040 --> 00:13:21.719 +the source code of the functions... + +00:13:21.720 --> 00:13:25.399 +these links only make sense in Emacs and + +00:13:25.400 --> 00:13:25.959 +in eev... + +00:13:25.960 --> 00:13:30.359 +and when we run a link like this one... + +00:13:30.360 --> 00:13:32.039 +it shows the source code in the + +00:13:32.040 --> 00:13:35.079 +window at the right. So, for some + +00:13:35.080 --> 00:13:37.879 +functions the source code is three lines, + +00:13:37.880 --> 00:13:39.999 +for other ones it's one line... and + +00:13:40.000 --> 00:13:44.879 +whatever. Anyway, let me go + +00:13:44.880 --> 00:13:47.039 +back... Lua can be used in many different + +00:13:47.040 --> 00:13:50.359 +styles... most people hate other people's + +00:13:50.360 --> 00:13:53.839 +styles... when I started using it in the + +00:13:53.840 --> 00:13:57.679 +year 2000 I learned most of the basic + +00:13:57.680 --> 00:13:59.839 +language in a single day - it was very + +00:13:59.840 --> 00:14:02.119 +similar to things that I was already + +00:14:02.120 --> 00:14:05.639 +using... and then I rewrote the the mini- + +00:14:05.640 --> 00:14:10.279 +language that I was using to + +00:14:10.280 --> 00:14:13.559 +generate the HTML for my pages + +00:14:13.560 --> 00:14:16.199 +in Lua... actually I had to rewrite it + +00:14:16.200 --> 00:14:18.079 +many times, but the first version I + +00:14:18.080 --> 00:14:21.519 +certainly did in my first weeks or first + +00:14:21.520 --> 00:14:22.519 +months using Lua... + +00:14:22.520 --> 00:14:27.279 +In the beginning I was just using + +00:14:27.280 --> 00:14:30.159 +it for writing programs that either + +00:14:30.160 --> 00:14:32.759 +didn't take any input at all - because + +00:14:32.760 --> 00:14:35.079 +the input was already in the source file - + +00:14:35.080 --> 00:14:40.599 +or that worked as Unix programs, + +00:14:40.600 --> 00:14:43.199 +that would read files + +00:14:43.200 --> 00:14:45.279 +and process these files in some way + +00:14:45.280 --> 00:14:48.999 +and output something. + +00:14:49.000 --> 00:14:52.319 +I mentioned the "basic language" here... + +00:14:52.320 --> 00:14:54.719 +I only learned how to use closures, + +00:14:54.720 --> 00:14:58.479 +metatables, and coroutines many years later... + +00:14:58.480 --> 00:15:02.399 +in the beginning, when I started using Lua, + +00:15:02.400 --> 00:15:04.199 +it didn't have a package manager... + +00:15:04.200 --> 00:15:06.799 +it appeared later, it is called + +00:15:06.800 --> 00:15:10.119 +Luarocks... it has had this package + +00:15:10.120 --> 00:15:13.279 +manager for several years, most + +00:15:13.280 --> 00:15:15.719 +of the rocks for Luarocks are poorly + +00:15:15.720 --> 00:15:18.959 +documented and hacker-unfriendly, + +00:15:18.960 --> 00:15:21.199 +so you can't rely just on the + +00:15:21.200 --> 00:15:23.679 +documentation and you can't rely just on the + +00:15:23.680 --> 00:15:26.719 +source code, because, I mean... if you are + +00:15:26.720 --> 00:15:29.159 +a genius of course you can, but for + +00:15:29.160 --> 00:15:31.479 +people who are either lazy, or dumb, or + +00:15:31.480 --> 00:15:34.279 +whatever, like me, or unfocused... + +00:15:34.280 --> 00:15:36.759 +the source code is hard to + +00:15:36.760 --> 00:15:38.959 +understand and hard to tinker with. + +00:15:38.960 --> 00:15:43.319 +Some rocks are excellent. The + +00:15:43.320 --> 00:15:46.599 +best rocks are well documented + +00:15:46.600 --> 00:15:48.719 +but they are hacker-unfriendly + +00:15:48.720 --> 00:15:50.999 +in a sense that I hope that + +00:15:51.000 --> 00:15:52.879 +I'll be able to explain soon. + +00:15:52.880 --> 00:15:54.999 +The best rocks use local + +00:15:55.000 --> 00:15:58.799 +variables and metatables a lot - + +00:15:58.800 --> 00:16:02.519 +so if you are beginner + +00:16:02.520 --> 00:16:03.799 +learning Lua you're not going to + +00:16:03.800 --> 00:16:06.159 +understand what their source code do... + +00:16:06.160 --> 00:16:08.519 +they use lots of dirty tricks. + +NOTE Object orientation in Lua + +00:16:08.520 --> 00:16:12.479 +Let me talk a bit about object + +00:16:12.480 --> 00:16:14.959 +orientation in Lua. It can be done in + +00:16:14.960 --> 00:16:15.879 +many ways... + +00:16:15.880 --> 00:16:18.999 +the main book about Lua, called + +00:16:19.000 --> 00:16:21.439 +"Programming in Lua", by one of the authors + +00:16:21.440 --> 00:16:23.959 +of the language, Roberto Ierusalimschy, + +00:16:23.960 --> 00:16:26.679 +presents several ways of doing + +00:16:26.680 --> 00:16:29.279 +object orientation in Lua... I hated all + +00:16:29.280 --> 00:16:33.199 +of these ways - and also the ways that I + +00:16:33.200 --> 00:16:34.519 +tried from the rocks. + +00:16:34.520 --> 00:16:38.559 +And then I wrote my own way + +00:16:38.560 --> 00:16:40.639 +of doing object orientation in Lua... it's + +00:16:40.640 --> 00:16:43.559 +very minimalistic, it's in this file here, + +00:16:43.560 --> 00:16:48.679 +eoo.lua... the main code is just this five + +00:16:48.680 --> 00:16:49.639 +lines here... + +00:16:49.640 --> 00:16:53.439 +and here's an example of how it works. + +00:16:53.440 --> 00:16:58.439 +Here we define the class Vector, + +00:16:58.440 --> 00:17:02.719 +with some metamethods... + +00:17:02.720 --> 00:17:05.959 +this metamethod here will tell Lua + +00:17:05.960 --> 00:17:08.319 +what to do when the + +00:17:08.320 --> 00:17:12.639 +user asks to add two vectors, this one + +00:17:12.640 --> 00:17:15.919 +here tells Lua what to do when the user + +00:17:15.920 --> 00:17:18.479 +asks Lua to convert a vector to a string, + +00:17:18.480 --> 00:17:21.439 +and... whatever, this one is + +00:17:21.440 --> 00:17:24.039 +something that I'm going to explain in a + +00:17:24.040 --> 00:17:27.479 +second. So, here we create a vector with + +00:17:27.480 --> 00:17:30.279 +these coordinates, 3 and 4... here we create + +00:17:30.280 --> 00:17:33.319 +another Vector... if we "print" here then Lua + +00:17:33.320 --> 00:17:36.439 +uses this function here, in the __tostring... + +00:17:36.440 --> 00:17:39.759 +if we add the two vectors it uses this + +00:17:39.760 --> 00:17:43.479 +function here, in the __add metamethod, and + +00:17:43.480 --> 00:17:45.359 +if we run the method :norm... + +00:17:45.360 --> 00:17:49.959 +it is defined here, in the table __index. + +00:17:49.960 --> 00:17:57.999 +Anyway... + +00:17:58.000 --> 00:18:02.439 +Even this thing being so small I used + +00:18:02.440 --> 00:18:04.719 +to forget how its innards worked all + +00:18:04.720 --> 00:18:08.119 +the time. Actually I always forget how + +00:18:08.120 --> 00:18:09.759 +things work and I have to remember them + +00:18:09.760 --> 00:18:12.479 +somehow... and I have to have + +00:18:12.480 --> 00:18:15.959 +tricks for remembering, and tricks for + +00:18:15.960 --> 00:18:18.719 +summarizing things, and diagrams, and so + +00:18:18.720 --> 00:18:22.199 +on. And every time that I forgot how this + +00:18:22.200 --> 00:18:24.799 +thing worked I went back to the + +00:18:24.800 --> 00:18:26.879 +source code, and then I looked at the + +00:18:26.880 --> 00:18:29.039 +diagrams... or, of course, in the + +00:18:29.040 --> 00:18:31.719 +first times I had to draw the diagrams... + +00:18:31.720 --> 00:18:35.239 +and I run the examples, and of course in + +00:18:35.240 --> 00:18:36.479 +in the beginning I thought that the code + +00:18:36.480 --> 00:18:39.119 +was clear and my examples were very + +00:18:39.120 --> 00:18:41.559 +brief, and so I had to rewrite the + +00:18:41.560 --> 00:18:44.719 +examples many times until they became, + +00:18:44.720 --> 00:18:45.639 +let's say... + +00:18:45.640 --> 00:18:47.759 +perfect. + +00:18:47.760 --> 00:18:52.599 +I was saying that Lua can be used in + +00:18:52.600 --> 00:18:56.359 +many ways, and in my way of using Lua - in + +00:18:56.360 --> 00:18:59.439 +my favorite way - everything can be + +00:18:59.440 --> 00:19:02.159 +inspected and modified from REPLs, + +00:19:02.160 --> 00:19:06.319 +like we can do in Emacs and in SmallTalk, + +00:19:06.320 --> 00:19:08.519 +or sort of. So, in my + +00:19:08.520 --> 00:19:10.239 +favorite way of using Lua there's no + +00:19:10.240 --> 00:19:12.679 +security at all, everything can be + +00:19:12.680 --> 00:19:14.919 +changed at all times. + +00:19:14.920 --> 00:19:19.119 +Of course most people hate that... + +NOTE My init file + +00:19:19.120 --> 00:19:22.599 +My init file has lots of classes... by the + +00:19:22.600 --> 00:19:26.079 +way, instead of keeping many small files + +00:19:26.080 --> 00:19:29.639 +with many things I put lots of stuff + +00:19:29.640 --> 00:19:31.279 +in just one big init file. + +00:19:31.280 --> 00:19:34.599 +My init file has lots of classes, + +00:19:34.600 --> 00:19:37.959 +and lots of global functions, and + +00:19:37.960 --> 00:19:41.799 +lots of cruft - and people hate that, + +00:19:41.800 --> 00:19:44.559 +of course. This is an example... + +00:19:44.560 --> 00:19:46.439 +this is the index at the top + +00:19:46.440 --> 00:19:48.359 +of my init file, + +00:19:48.360 --> 00:19:53.119 +the classes start here, and then + +00:19:53.120 --> 00:19:59.119 +we have some functions, and + +00:19:59.120 --> 00:20:01.199 +then we have functions that load + +00:20:01.200 --> 00:20:03.839 +certain packages, and then we have... cruft. + +00:20:03.840 --> 00:20:04.919 +Whatever. + +00:20:04.920 --> 00:20:08.119 +Most people think that my style + +00:20:08.120 --> 00:20:10.279 +of using Lua is dirty, and dangerous... + +00:20:10.280 --> 00:20:12.959 +and they wouldn't touch my Lua code + +00:20:12.960 --> 00:20:15.479 +with a 10 feet pole... but most of the + +00:20:15.480 --> 00:20:18.599 +things that I'm going to present here in + +00:20:18.600 --> 00:20:23.199 +this presentation are ideas that should + +00:20:23.200 --> 00:20:28.159 +be easy to port to other environments + +00:20:28.160 --> 00:20:32.279 +and other languages, especially the + +00:20:32.280 --> 00:20:35.279 +diagrams... so the code is not so important. + +NOTE LaTeX and LuaLaTeX + +00:20:35.280 --> 00:20:39.039 +Now let me talk a bit about LuaLaTeX, + +00:20:39.040 --> 00:20:41.359 +that is LaTeX with a Lua interpreter + +00:20:41.360 --> 00:20:44.559 +embedded inside, and two ways + +00:20:44.560 --> 00:20:48.839 +of generating pictures in LaTeX: TikZ, + +00:20:48.840 --> 00:20:54.439 +that is very famous, and Pict2e, that is not + +00:20:54.440 --> 00:20:57.359 +very famous and that is very low level... + +00:20:57.360 --> 00:21:02.359 +and I think that not many people use it. + +00:21:02.360 --> 00:21:04.119 +I said before that when I + +00:21:04.120 --> 00:21:06.919 +learned Lua I realized that it was + +00:21:06.920 --> 00:21:09.199 +very good for writing little + +00:21:09.200 --> 00:21:14.919 +languages. I was doing my PhD at the + +00:21:14.920 --> 00:21:19.839 +time and typesetting the diagrams for + +00:21:19.840 --> 00:21:24.039 +my PhD thesis was very boring, so + +00:21:24.040 --> 00:21:29.879 +one of the things that I did was that I + +00:21:29.880 --> 00:21:34.439 +created a little language for typesetting + +00:21:34.440 --> 00:21:36.359 +the diagrams for me. it was + +00:21:36.360 --> 00:21:38.879 +called Dednat because initially + +00:21:38.880 --> 00:21:41.039 +it only generated diagrams for + +00:21:41.040 --> 00:21:43.759 +Natural Deduction, and then it had + +00:21:43.760 --> 00:21:45.119 +several versions... + +00:21:45.120 --> 00:21:46.679 +these are the slides for my + +00:21:46.680 --> 00:21:52.159 +presentation about Dednat6... "Dednat6 is + +00:21:52.160 --> 00:21:56.159 +an extensible semi-preprocessor for + +00:21:56.160 --> 00:22:01.159 +LuaLaTeX that understands diagrams in + +00:22:01.160 --> 00:22:05.359 +ASCII art"... in the sense that when I have + +00:22:05.360 --> 00:22:11.399 +a .tex file that has this, and when + +00:22:11.400 --> 00:22:13.279 +Dednat6 is loaded, + +00:22:13.280 --> 00:22:15.039 +when I give the right commands + +00:22:15.040 --> 00:22:19.559 +Dednat6 interprets this block here as + +00:22:19.560 --> 00:22:22.559 +something that defines this + +00:22:22.560 --> 00:22:28.239 +diagram... oops, sorry, it interprets this + +00:22:28.240 --> 00:22:30.599 +diagram here, this diagram in + +00:22:30.600 --> 00:22:34.879 +comments here, as something that defines + +00:22:34.880 --> 00:22:39.759 +a diagram called foo... a deduction called + +00:22:39.760 --> 00:22:41.439 +foo, and it generates this code here... + +00:22:41.440 --> 00:22:44.239 +so that we can just invoke + +00:22:44.240 --> 00:22:45.519 +the definition of the + +00:22:45.520 --> 00:22:47.719 +deduction by typing \ded{foo}. + +00:22:47.720 --> 00:22:50.759 +And Dednat6 also + +00:22:50.760 --> 00:22:57.159 +supports another language for typesetting + +00:22:57.160 --> 00:22:59.639 +bidimensional diagrams with + +00:22:59.640 --> 00:23:05.399 +arrows and stuff for category Theory and + +00:23:05.400 --> 00:23:08.519 +blah blah blah... the specifications of + +00:23:08.520 --> 00:23:12.039 +these diagrams look like this... + +00:23:12.040 --> 00:23:14.559 +here is a... sorry, here is a very good + +00:23:14.560 --> 00:23:16.719 +example, this is a huge diagram... + +00:23:16.720 --> 00:23:18.599 +sorry, one second... + +00:23:18.600 --> 00:23:20.399 +so, the source code that generates + +00:23:20.400 --> 00:23:25.119 +this diagram here is just this thing at + +00:23:25.120 --> 00:23:32.039 +the left, so it's very visual... we can + +00:23:32.040 --> 00:23:35.679 +typeset the diagram in ASCII art here and + +00:23:35.680 --> 00:23:38.759 +then in this part here we tell how + +00:23:38.760 --> 00:23:41.279 +the nodes are to be joined, which + +00:23:41.280 --> 00:23:43.799 +arrows have to to have annotations, and + +00:23:43.800 --> 00:23:45.039 +so on... + +00:23:45.040 --> 00:23:46.799 +and this language is extensible in + +00:23:46.800 --> 00:23:48.679 +the sense that... uh, where's that... + +00:23:48.680 --> 00:23:52.559 +here: comments that start with "%:" + +00:23:52.560 --> 00:23:54.119 +are interpreted as + +00:23:54.120 --> 00:23:56.079 +definitions for tree diagrams, + +00:23:56.080 --> 00:23:58.559 +lines that start with "%D" + +00:23:58.560 --> 00:24:00.639 +define 2D diagrams with arrows and + +00:24:00.640 --> 00:24:04.279 +stuff, and lines that start with "%L" + +00:24:04.280 --> 00:24:06.759 +contain blocks of Lua code + +00:24:06.760 --> 00:24:09.479 +that we can use to extend the interpreter + +00:24:09.480 --> 00:24:10.439 +on-the-fly... + +00:24:10.440 --> 00:24:12.679 +anyway, here are some recent + +00:24:12.680 --> 00:24:15.319 +examples of diagrams that I used + +00:24:15.320 --> 00:24:19.839 +Dednat6 to typeset... this diagram + +00:24:19.840 --> 00:24:21.919 +here was generated by this + +00:24:21.920 --> 00:24:22.879 +specification here... + +00:24:22.880 --> 00:24:27.239 +and this diagram here with the + +00:24:27.240 --> 00:24:30.719 +curved arrows was generated by this + +00:24:30.720 --> 00:24:32.719 +specification here. + +00:24:32.720 --> 00:24:39.079 +So, Dednat6 was very easy to extend, + +00:24:39.080 --> 00:24:41.879 +and at some point I started to use it + +00:24:41.880 --> 00:24:44.679 +to generate diagrams using Pict2e - + +00:24:44.680 --> 00:24:47.359 +mainly for the classes that I give + +00:24:47.360 --> 00:24:50.079 +at the University... I teach mathematics and + +00:24:50.080 --> 00:24:57.239 +whatever... in a bad place. Whatever... + +00:24:57.240 --> 00:25:00.039 +Let me show an animation... here is a + +00:25:00.040 --> 00:25:02.479 +diagram that I generated with Dednat6, + +00:25:02.480 --> 00:25:06.319 +and it is a flip book animation, like... we + +00:25:06.320 --> 00:25:09.279 +type PgUp and PgDn and we go + +00:25:09.280 --> 00:25:11.119 +to the next page of the book and to the + +00:25:11.120 --> 00:25:12.439 +previous page of the book... + +00:25:12.440 --> 00:25:16.279 +and here is the source code that generates + +00:25:16.280 --> 00:25:19.159 +that. This source code is not very visual, + +00:25:19.160 --> 00:25:22.559 +so it's quite clumsy to edit that + +00:25:22.560 --> 00:25:27.519 +diagram directly in the .tex file like + +00:25:27.520 --> 00:25:28.079 +that... + +NOTE Manim + +00:25:28.080 --> 00:25:30.199 +These diagrams were inspired + +00:25:30.200 --> 00:25:33.039 +by something called my Manim, that... + +00:25:33.040 --> 00:25:37.559 +I forgot the name of the guy, but + +00:25:37.560 --> 00:25:41.479 +it's a guy that makes many videos about + +00:25:41.480 --> 00:25:44.839 +Mathematics, and he created this library + +00:25:44.840 --> 00:25:48.599 +called Manim for generating his + +00:25:48.600 --> 00:25:51.839 +animations, and other people adapted + +00:25:51.840 --> 00:25:55.919 +his library to make it more accessible... + +00:25:55.920 --> 00:25:59.359 +I tried to learn it, but + +00:25:59.360 --> 00:26:01.199 +each animation, even an animation + +00:26:01.200 --> 00:26:03.679 +that has very few frames... each + +00:26:03.680 --> 00:26:07.319 +animation took ages to render, so it + +00:26:07.320 --> 00:26:11.159 +wasn't fun... and animations in PDFs can + +00:26:11.160 --> 00:26:13.639 +be rendered in seconds. So these + +00:26:13.640 --> 00:26:18.679 +things were fun for me, because my laptop + +00:26:18.680 --> 00:26:24.359 +is very very slow, and my Manim was not fun. + +NOTE Generating diagrams from REPLs + +00:26:24.360 --> 00:26:27.359 +Anyway, writing code like this + +00:26:27.360 --> 00:26:32.719 +inside a .tex file was not very + +00:26:32.720 --> 00:26:35.519 +fun because it was hard to + +00:26:35.520 --> 00:26:38.719 +debug... so in 2022 I started to play + +00:26:38.720 --> 00:26:41.319 +with ways of generating these + +00:26:41.320 --> 00:26:43.839 +diagrams from REPLs, and I found a + +00:26:43.840 --> 00:26:47.319 +way for Pict2e and a way for TikZ... + +00:26:47.320 --> 00:26:50.159 +each one of these ways became a video... + +00:26:50.160 --> 00:26:53.679 +if you go to the list of first-class + +00:26:53.680 --> 00:26:57.719 +videos of eev you're going to see + +00:26:57.720 --> 00:26:59.919 +that there's a video about Pict2e here + +00:26:59.920 --> 00:27:03.399 +here and a video about TikZ... + +00:27:03.400 --> 00:27:05.759 +here you have some some information + +00:27:05.760 --> 00:27:09.839 +like length, an explanation, etc... + +00:27:09.840 --> 00:27:11.719 +and here are the pages for these videos. + +00:27:11.720 --> 00:27:15.999 +My page about the video about Pict2e + +00:27:16.000 --> 00:27:20.079 +looks like this, it has some diagrams... + +00:27:20.080 --> 00:27:23.919 +whatever... and this one is much + +00:27:23.920 --> 00:27:26.679 +nicer, and a lot of people + +00:27:26.680 --> 00:27:30.599 +watched that video... I mean, I think + +00:27:30.600 --> 00:27:33.719 +that 250 people watched it - for me that's + +00:27:33.720 --> 00:27:35.599 +a million of people... + +00:27:35.600 --> 00:27:39.159 +and this video is about how to + +00:27:39.160 --> 00:27:44.079 +extract diagrams from the manual... from + +00:27:44.080 --> 00:27:46.599 +the TikZ manual and how to run those + +00:27:46.600 --> 00:27:49.759 +examples in a REPL and modify + +00:27:49.760 --> 00:27:53.159 +them bit by bit... this is a a + +00:27:53.160 --> 00:27:57.439 +screenshot... but let me go back. + +00:27:57.440 --> 00:28:00.959 +At that point these things were just + +00:28:00.960 --> 00:28:03.239 +prototypes, the code was not very nice... + +00:28:03.240 --> 00:28:07.519 +and in this year I wrote... I was able + +00:28:07.520 --> 00:28:12.399 +to unify those two ways of generating PDFs, + +00:28:12.400 --> 00:28:16.039 +the one for TikZ and the one for Pict2e, + +00:28:16.040 --> 00:28:18.719 +and I unified them with many other + +00:28:18.720 --> 00:28:20.879 +things that generated diagrams. + +00:28:20.880 --> 00:28:24.279 +The basis of these things is + +00:28:24.280 --> 00:28:29.319 +something called Show2.lua... I'm not going + +00:28:29.320 --> 00:28:35.759 +to show its details now, but its + +00:28:35.760 --> 00:28:39.079 +extension that generates TikZ code + +00:28:39.080 --> 00:28:43.039 +is just this, so we can specify a + +00:28:43.040 --> 00:28:45.799 +diagram with just a block like this, + +00:28:45.800 --> 00:28:49.079 +and then uh if we + +00:28:49.080 --> 00:28:54.239 +run :show00() it returns a string + +00:28:54.240 --> 00:28:56.199 +that is just the body... the inner + +00:28:56.200 --> 00:29:00.279 +body of the .tex file, if we run this we + +00:29:00.280 --> 00:29:02.999 +see the whole .tex file, and if we run + +00:29:03.000 --> 00:29:05.119 +this we save the .tex file and we + +00:29:05.120 --> 00:29:08.119 +compile the .tex file to generate a PDF... + +00:29:08.120 --> 00:29:10.959 +and if we run this we show the PDF in + +00:29:10.960 --> 00:29:14.239 +the lower right window. + +00:29:14.240 --> 00:29:17.759 +And that's the same thing for all + +00:29:17.760 --> 00:29:20.199 +my recent programs that generate + +00:29:20.200 --> 00:29:22.439 +PDFs - they are all + +00:29:22.440 --> 00:29:26.199 +integrated... here is the one that... + +00:29:26.200 --> 00:29:29.359 +the basis for all my modules that generate + +00:29:29.360 --> 00:29:30.719 +diagrams with Pict2e... + +00:29:30.720 --> 00:29:34.879 +its demos are not very interesting, + +00:29:34.880 --> 00:29:36.799 +so let me show some demos of + +00:29:36.800 --> 00:29:39.759 +extensions that do interesting things... + +00:29:39.760 --> 00:29:45.319 +so, this is a diagram that I created + +00:29:45.320 --> 00:29:47.479 +by editing it in a REPL... + +00:29:47.480 --> 00:29:51.279 +I create several Pict objects here... + +00:29:51.280 --> 00:29:54.479 +and if I execute this it + +00:29:54.480 --> 00:29:59.959 +compiles an object, generates a PDF, and + +00:29:59.960 --> 00:30:04.759 +if I tap this... here is the PDF. + +00:30:04.760 --> 00:30:07.599 +And if I just ask Lua to + +00:30:07.600 --> 00:30:10.079 +display what is "pux", here, + +00:30:10.080 --> 00:30:15.719 +it shows the source code in Pict2e + +00:30:15.720 --> 00:30:17.999 +of the diagram... and the + +00:30:18.000 --> 00:30:20.959 +nice thing is that it is indented, so + +00:30:20.960 --> 00:30:23.599 +it's easy to debug the Pict2e code. + +00:30:23.600 --> 00:30:25.919 +If anyone is interested the + +00:30:25.920 --> 00:30:28.639 +module that does the tricks for + +00:30:28.640 --> 00:30:31.879 +indentation is very easy to understand... + +00:30:31.880 --> 00:30:35.959 +it has lots of tests and test blocks, + +00:30:35.960 --> 00:30:38.599 +and I think that its data + +00:30:38.600 --> 00:30:42.079 +structures are easy to understand. + +00:30:42.080 --> 00:30:44.359 +Anyway... here is another + +00:30:44.360 --> 00:30:51.359 +example. The :show() is + +00:30:51.360 --> 00:30:56.439 +here... it generates a 3D diagram. + +NOTE Parsers + +00:30:56.440 --> 00:31:06.279 +Now let me talk about parsers and + +00:31:06.280 --> 00:31:09.559 +REPLs in VERY strange places... I mean, + +00:31:09.560 --> 00:31:13.359 +using REPLs to build parsers step by step + +00:31:13.360 --> 00:31:17.959 +and" replacing parts by more complex + +00:31:17.960 --> 00:31:23.039 +parts. So, I said that Lua is very + +00:31:23.040 --> 00:31:28.279 +minimalistic, and everybody knows that + +00:31:28.280 --> 00:31:30.759 +implementations of regular expressions + +00:31:30.760 --> 00:31:32.479 +are big and complex.. + +00:31:32.480 --> 00:31:34.679 +so, instead of coming with + +00:31:34.680 --> 00:31:37.439 +full regular expressions Lua comes with + +00:31:37.440 --> 00:31:39.879 +something called "patterns" and a + +00:31:39.880 --> 00:31:43.839 +library function called "string.match". + +00:31:43.840 --> 00:31:44.599 +Here is + +00:31:44.600 --> 00:31:50.319 +a copy of the part of the manual that + +00:31:50.320 --> 00:31:53.399 +explains the syntax... a part of the + +00:31:53.400 --> 00:31:57.159 +syntax of of patterns... here's how + +00:31:57.160 --> 00:31:59.279 +string.match is described in the + +00:31:59.280 --> 00:32:03.199 +manual - it's just this... "looks for + +00:32:03.200 --> 00:32:05.359 +the first match of pattern in the string + +00:32:05.360 --> 00:32:08.039 +as blah blah blah"... and then we have to + +00:32:08.040 --> 00:32:10.159 +go to the other section of the menual + +00:32:10.160 --> 00:32:11.479 +that explains patterns. + +00:32:11.480 --> 00:32:20.079 +Lua patterns are so simple, + +00:32:20.080 --> 00:32:23.159 +so limited, that they don't even + +00:32:23.160 --> 00:32:26.519 +have the the alternation operator... + +00:32:26.520 --> 00:32:29.759 +here is how it is described in the + +00:32:29.760 --> 00:32:31.599 +elisp manual - + +00:32:31.600 --> 00:32:36.039 +backslash-pipe specifies + +00:32:36.040 --> 00:32:40.359 +an alternative, blah blah blah. + +00:32:40.360 --> 00:32:42.879 +When we want to to build more + +00:32:42.880 --> 00:32:45.319 +complex... regular expressions, + +00:32:45.320 --> 00:32:49.199 +patterns, grammars, etc... we have to use + +00:32:49.200 --> 00:32:52.679 +an external library for that... no, + +00:32:52.680 --> 00:32:56.279 +sorry, a library that is external + +00:32:56.280 --> 00:32:58.239 +but that was written by one of the + +00:32:58.240 --> 00:33:00.879 +authors of Lua itself. This library + +00:33:00.880 --> 00:33:05.879 +is called Lpeg, and its manual says... + +00:33:05.880 --> 00:33:09.599 +"Lpeg is a new pattern matching library for + +00:33:09.600 --> 00:33:12.039 +Lua based on Parsing Expression Grammars + +00:33:12.040 --> 00:33:18.759 +(PEGs)". The manual is very terse, I + +00:33:18.760 --> 00:33:21.559 +found it incredibly hard to read... it + +00:33:21.560 --> 00:33:25.439 +doesn't have any diagrams - it has some + +00:33:25.440 --> 00:33:29.759 +examples, though... and the Lua Wiki + +00:33:29.760 --> 00:33:33.879 +has a big page called Lpeg Tutorial + +00:33:33.880 --> 00:33:35.359 +with lots of examples... + +00:33:35.360 --> 00:33:38.879 +but it it also doesn't have + +00:33:38.880 --> 00:33:41.199 +diagrams and I found some things + +00:33:41.200 --> 00:33:42.719 +incredibly hard to understand. + +00:33:42.720 --> 00:33:45.879 +For example, this is something that is in + +00:33:45.880 --> 00:33:48.879 +the the manual of Lpeg that I saw and I + +00:33:48.880 --> 00:33:51.639 +thought: "Wow, great! This makes all sense + +00:33:51.640 --> 00:33:53.159 +and is going to be very useful!"... + +00:33:53.160 --> 00:33:54.199 +it's a way to to build + +00:33:54.200 --> 00:33:57.199 +grammars that can be recursive, + +00:33:57.200 --> 00:34:01.359 +and they sort of can encode BNF + +00:34:01.360 --> 00:34:03.439 +grammars... we just have to translate the + +00:34:03.440 --> 00:34:06.479 +BNF a bit to get rid of some + +00:34:06.480 --> 00:34:08.079 +recursions and to translate them to + +00:34:08.080 --> 00:34:08.999 +something else. + +00:34:09.000 --> 00:34:11.919 +And the manual also has some things + +00:34:11.920 --> 00:34:15.159 +that I thought: "Oh, no! I don't have any + +00:34:15.160 --> 00:34:18.359 +idea of what this thing does"... and in fact + +00:34:18.360 --> 00:34:20.399 +I saw these things for the first + +00:34:20.400 --> 00:34:22.359 +time more than 10 years ago and they + +00:34:22.360 --> 00:34:26.079 +only started to make sense one year ago. + +00:34:26.080 --> 00:34:30.519 +One example is group captures. + +00:34:30.520 --> 00:34:36.359 +Lpeg also comes with a + +00:34:36.360 --> 00:34:38.719 +module called the Re module... let me + +00:34:38.720 --> 00:34:41.719 +pronounce as it in Portuguese - the Re + +00:34:41.720 --> 00:34:45.759 +module... its manual says: "The Re + +00:34:45.760 --> 00:34:48.199 +module (provided by the file re.lua in the + +00:34:48.200 --> 00:34:51.159 +distribution) supports a somewhat conventional + +00:34:51.160 --> 00:34:56.239 +regular expression syntax for pattern usage + +00:34:56.240 --> 00:34:58.679 +within lpeg"... and + +00:34:58.680 --> 00:35:03.519 +this is a quick reference... this + +00:35:03.520 --> 00:35:06.319 +thing is very brief, it has some nice + +00:35:06.320 --> 00:35:08.919 +examples but it's hard to understand anyway... + +00:35:08.920 --> 00:35:13.199 +and here are some comments about + +00:35:13.200 --> 00:35:17.279 +my attempts to learn Re.lua. This is + +00:35:17.280 --> 00:35:20.639 +a class... in this case it's a very small + +00:35:20.640 --> 00:35:24.839 +class... this file implements a :pm() + +00:35:24.840 --> 00:35:28.679 +method - I'm going to show examples of + +00:35:28.680 --> 00:35:32.239 +other :pm() methods very soon - so, this is + +00:35:32.240 --> 00:35:35.799 +a :pm() method for Re.lua that lets us + +00:35:35.800 --> 00:35:38.719 +compare the syntax of Lua patterns, Lpeg, + +00:35:38.720 --> 00:35:43.999 +and Re... let's see this example here... so, + +00:35:44.000 --> 00:35:47.319 +if we run this it loads my version of + +00:35:47.320 --> 00:35:52.799 +lpeg... no, sorry, my version of lpegrex... + +00:35:52.800 --> 00:35:57.119 +and it shows that when we apply + +00:35:57.120 --> 00:36:01.199 +the :pm() method to this Lua pattern, this + +00:36:01.200 --> 00:36:04.879 +lpeg pattern, and this Re pattern + +00:36:04.880 --> 00:36:07.999 +they all give the same results. So we can + +00:36:08.000 --> 00:36:10.799 +use this thing... this kind of thing here + +00:36:10.800 --> 00:36:14.119 +to show how to translate from Lua + +00:36:14.120 --> 00:36:16.519 +patterns, that are familiar because + +00:36:16.520 --> 00:36:18.519 +they're similar to regular expressions, + +00:36:18.520 --> 00:36:20.199 +only weaker... + +00:36:20.200 --> 00:36:24.799 +to lpeg, that is super weird + +00:36:24.800 --> 00:36:27.759 +and to Re, that is not so weird. + +00:36:27.760 --> 00:36:35.159 +Anyway, the comment says that in 2012 + +00:36:35.160 --> 00:36:37.519 +I had a project that needed a + +00:36:37.520 --> 00:36:40.479 +precedence passer that could parse + +00:36:40.480 --> 00:36:43.239 +arithmetical expressions with the right + +00:36:43.240 --> 00:36:46.639 +precedences... and at that point I was + +00:36:46.640 --> 00:36:49.919 +still struggling with pure lpeg, and I + +00:36:49.920 --> 00:36:52.359 +couldn't do much with it, so I tried to + +00:36:52.360 --> 00:36:55.519 +learn Re.lua instead, and I wrote this old + +00:36:55.520 --> 00:36:56.319 +class here... + +00:36:56.320 --> 00:37:01.039 +that allowed me to use a preprocessor + +00:37:01.040 --> 00:37:03.279 +on patterns for Lua. And the thing is that + +00:37:03.280 --> 00:37:04.879 +with this preprocessor I could + +00:37:04.880 --> 00:37:07.839 +specify precedence grammars using this + +00:37:07.840 --> 00:37:11.879 +thing here, that worked, but was super + +00:37:11.880 --> 00:37:15.999 +clumsy... and I gave up after a few attempts. + +00:37:16.000 --> 00:37:21.879 +and in 2022 I heard about something + +00:37:21.880 --> 00:37:23.239 +called lpegrex, + +00:37:23.240 --> 00:37:29.799 +that was a... a kind of extension or Re, + +00:37:29.800 --> 00:37:32.879 +and it was much more powerful than re.lua, + +00:37:32.880 --> 00:37:34.919 +but after a while I realized that it + +00:37:34.920 --> 00:37:37.639 +had the same defects as re.lua... + +00:37:37.640 --> 00:37:40.839 +and let me explain that, because + +00:37:40.840 --> 00:37:44.439 +it has all to do with the things about + +00:37:44.440 --> 00:37:48.039 +black boxes and magic that I told in the + +00:37:48.040 --> 00:37:52.919 +beginning. Both... I mean, sorry, neither + +00:37:52.920 --> 00:37:57.199 +re.lua or lpegrex had some features that + +00:37:57.200 --> 00:38:00.799 +I needed... they didn't let us explore... + +00:38:00.800 --> 00:38:03.679 +sorry, they received a pattern that was + +00:38:03.680 --> 00:38:06.839 +specified as a string, and it converted + +00:38:06.840 --> 00:38:09.679 +that into an lpeg pattern, but it didn't + +00:38:09.680 --> 00:38:12.559 +let us explore the the lpeg patterns + +00:38:12.560 --> 00:38:15.159 +that it generated... + +00:38:15.160 --> 00:38:18.759 +their code was written in a way + +00:38:18.760 --> 00:38:21.319 +that was REPL-unfriendly - I + +00:38:21.320 --> 00:38:24.279 +couldn't modify parts of the code + +00:38:24.280 --> 00:38:28.399 +bit by bit in a REPL and try to change + +00:38:28.400 --> 00:38:31.719 +the code without changing the + +00:38:31.720 --> 00:38:34.199 +original file... the code was very + +00:38:34.200 --> 00:38:36.839 +hard to explore, to hack, and to extend - + +00:38:36.840 --> 00:38:39.159 +in my opinion... the documentation was not + +00:38:39.160 --> 00:38:43.319 +very clear... and I sent one or two messages + +00:38:43.320 --> 00:38:47.159 +to the the developer of lpegrex and... + +00:38:47.160 --> 00:38:50.759 +he was too busy to help me. He + +00:38:50.760 --> 00:38:53.959 +answered it very briefly, and, uh, to be + +00:38:53.960 --> 00:38:56.599 +honest I felt... rejected. I felt that I + +00:38:56.600 --> 00:38:58.679 +wasn't doing anything interesting... + +00:38:58.680 --> 00:39:03.399 +whatever, whatever... + +00:39:03.400 --> 00:39:09.239 +So, in 2022 I was trying to learn lpegrex + +00:39:09.240 --> 00:39:11.559 +because I was thinking that it would + +00:39:11.560 --> 00:39:13.719 +solve my problems - but it didn't... + +00:39:13.720 --> 00:39:16.479 +it didn't have the features that I needed, + +00:39:16.480 --> 00:39:20.919 +it was hard to extend, hard to explore, + +00:39:20.920 --> 00:39:23.279 +and hard to debug, and I + +00:39:23.280 --> 00:39:25.039 +decided to rewrite it in a more + +00:39:25.040 --> 00:39:30.639 +hacker-friendly way - in the sense that... + +00:39:30.640 --> 00:39:33.759 +was modular, and I could replace any + +00:39:33.760 --> 00:39:35.399 +part of the module from a REPL... + +NOTE ELpeg1.lua + +00:39:35.400 --> 00:39:43.679 +My version of it was called ELpeg1.lua... + +00:39:43.680 --> 00:39:47.679 +and I decided that in my version I + +00:39:47.680 --> 00:39:49.639 +wouldn't have the part that + +00:39:49.640 --> 00:39:54.879 +receives a grammar specified as a string + +00:39:54.880 --> 00:39:57.519 +and converts that to lpeg... I would + +00:39:57.520 --> 00:40:00.959 +just have the backend part, that are the + +00:40:00.960 --> 00:40:03.999 +functions in lpeg that let us specify + +00:40:04.000 --> 00:40:05.479 +powerful grammars. + +00:40:05.480 --> 00:40:11.759 +Let me go back. Let me explain a + +00:40:11.760 --> 00:40:15.519 +bit about lpeg... Lua has + +00:40:15.520 --> 00:40:21.599 +coercions: the + expects to receive + +00:40:21.600 --> 00:40:23.999 +true numbers, and if one of its arguments, + +00:40:24.000 --> 00:40:26.999 +or both of them, are strings, it converts + +00:40:27.000 --> 00:40:29.839 +the string... the strings to numbers so in + +00:40:29.840 --> 00:40:33.519 +this case here, 2+"3", + +00:40:33.520 --> 00:40:36.159 +it returns the number 5, + +00:40:36.160 --> 00:40:39.359 +and this is the concatenation + +00:40:39.360 --> 00:40:42.119 +operator... it expects to receive + +00:40:42.120 --> 00:40:44.999 +strings, so in this case it will + +00:40:45.000 --> 00:40:47.359 +convert the number 2 to the string "2", + +00:40:47.360 --> 00:40:50.279 +and the concatenation of thes two + +00:40:50.280 --> 00:40:54.479 +things will be 23... oops, sorry, "23" + +00:40:54.480 --> 00:40:56.279 +as a string. + +00:40:56.280 --> 00:40:58.519 +Lpeg also has some coercions. + +00:40:58.520 --> 00:41:01.759 +I usually set these + +00:41:01.760 --> 00:41:05.799 +globals to let me write my grammars + +00:41:05.800 --> 00:41:09.719 +in a very compact way, so instead + +00:41:09.720 --> 00:41:14.759 +of lpeg.B, lpeg.C, etc I use these globals, + +00:41:14.760 --> 00:41:18.359 +like uppercase B, uppercase C, and so on... + +00:41:18.360 --> 00:41:21.679 +and with these globals I can write + +00:41:21.680 --> 00:41:26.759 +things like this: C(1)*"_"... + +00:41:26.760 --> 00:41:33.199 +and lpeg knows that lpeg.C... + +00:41:33.200 --> 00:41:38.879 +it sort of expands this to lpeg.C, + +00:41:38.880 --> 00:41:42.039 +but lpeg.C expects to receive + +00:41:42.040 --> 00:41:44.839 +an lpeg pattern, and 1 is not yet an + +00:41:44.840 --> 00:41:47.879 +lpeg pattern, so it is coerced into an + +00:41:47.880 --> 00:41:51.799 +lpeg pattern by calling lpeg.P, + +00:41:51.800 --> 00:41:55.679 +so this short thing here becomes + +00:41:55.680 --> 00:42:03.399 +equivalent to lpeg.C(lpeg.P(1)), and the + +00:42:03.400 --> 00:42:07.399 +multiplication, when at least one of its + +00:42:07.400 --> 00:42:10.759 +arguments is an lpeg pattern... it expects + +00:42:10.760 --> 00:42:13.199 +to receive two lpeg patterns, and in + +00:42:13.200 --> 00:42:15.239 +this case the one at the right is + +00:42:15.240 --> 00:42:18.319 +just a string, so it is coerced to an lpeg + +00:42:18.320 --> 00:42:20.079 +pattern by using lpeg.P. + +00:42:20.080 --> 00:42:25.599 +With this idea we can sort of + +00:42:25.600 --> 00:42:28.439 +understand the comparison here. I mean, + +00:42:28.440 --> 00:42:31.719 +let me run it again... this first part is + +00:42:31.720 --> 00:42:34.679 +very similar to a regular expression + +00:42:34.680 --> 00:42:35.359 +here at the left... + +00:42:35.360 --> 00:42:39.759 +and when we apply this... Lua pattern + +00:42:39.760 --> 00:42:43.639 +to this subject here the result + +00:42:43.640 --> 00:42:47.799 +is this thing here, this thing, this + +00:42:47.800 --> 00:42:54.319 +thing and this thing... I'm going to + +00:42:54.320 --> 00:42:56.119 +call each one of these results + +00:42:56.120 --> 00:42:59.519 +"captures", so each of these things + +00:42:59.520 --> 00:43:03.319 +between parentheses "captures" a substring + +00:43:03.320 --> 00:43:06.039 +of the original string and these + +00:43:06.040 --> 00:43:08.559 +captured substrings are returned in a + +00:43:08.560 --> 00:43:11.839 +certain order. Here is how to express the + +00:43:11.840 --> 00:43:12.759 +same thing in lpeg... + +00:43:12.760 --> 00:43:15.919 +it's very cryptic but it's a + +00:43:15.920 --> 00:43:20.719 +good way to understand the some basic + +00:43:20.720 --> 00:43:23.879 +operators of lpeg, I mean we can look at + +00:43:23.880 --> 00:43:26.479 +the manual and understand and + +00:43:26.480 --> 00:43:30.519 +what C, S and R do, and also + +00:43:30.520 --> 00:43:37.959 +exponentiation... and this strange thing + +00:43:37.960 --> 00:43:41.319 +here receives this string here, runs + +00:43:41.320 --> 00:43:43.279 +a function that I have defined, that + +00:43:43.280 --> 00:43:46.039 +converts it to an object of a certain + +00:43:46.040 --> 00:43:47.759 +class, and that class + +00:43:47.760 --> 00:43:52.399 +represents Re patterns, so this thing + +00:43:52.400 --> 00:43:54.479 +is treated as a pattern for re.lua, + +00:43:54.480 --> 00:43:56.479 +and it is matched against the string, + +00:43:56.480 --> 00:43:59.439 +and it returns the same thing as the + +00:43:59.440 --> 00:44:02.559 +other one. + +00:44:02.560 --> 00:44:05.519 +Also, this thing here also has a + +00:44:05.520 --> 00:44:08.479 +comparison with lpegrex, but these + +00:44:08.480 --> 00:44:11.559 +patterns are very trivial, they + +00:44:11.560 --> 00:44:13.359 +don't do anything very strange... + +00:44:13.360 --> 00:44:15.759 +so let's go back and see what + +00:44:15.760 --> 00:44:18.239 +kinds of very strange things there are. + +00:44:18.240 --> 00:44:26.559 +Here is the page of lpegrex at github, + +00:44:26.560 --> 00:44:29.719 +here's the documentation... + +00:44:29.720 --> 00:44:32.439 +it's relatively brief, + +00:44:32.440 --> 00:44:35.239 +it explains lpegrex as being an + +00:44:35.240 --> 00:44:39.719 +extension of Re.lua, so it explains + +00:44:39.720 --> 00:44:42.879 +mainly the additional features... here is a + +00:44:42.880 --> 00:44:45.119 +quick reference that explains only the + +00:44:45.120 --> 00:44:46.359 +additional features... + +00:44:46.360 --> 00:44:49.639 +some of the these things + +00:44:49.640 --> 00:44:50.919 +I was able to understand + +00:44:50.920 --> 00:44:57.559 +by struggling a lot, and some I wasn't + +00:44:57.560 --> 00:45:02.439 +able to even by spending several evenings + +00:45:02.440 --> 00:45:04.319 +try to to build examples... + +00:45:04.320 --> 00:45:12.879 +and this is something very nice. Lpegrex + +00:45:12.880 --> 00:45:15.879 +comes with some example parsers... and + +00:45:15.880 --> 00:45:18.679 +here is a parser that parses the Lua + +00:45:18.680 --> 00:45:22.479 +grammar - I mean, this is the the grammar + +00:45:22.480 --> 00:45:25.959 +for Lua 5.4 at the end of the + +00:45:25.960 --> 00:45:31.199 +reference manual... it's just this... this + +00:45:31.200 --> 00:45:34.799 +is in a kind of BNF, and this is the BNF + +00:45:34.800 --> 00:45:35.599 +translated + +00:45:35.600 --> 00:45:39.919 +to the language of lpegrex, so this + +00:45:39.920 --> 00:45:43.039 +thing uses many constructions that are + +00:45:43.040 --> 00:45:47.999 +in re.lua and some extra constructions that + +00:45:48.000 --> 00:45:50.959 +are described here... and with these + +00:45:50.960 --> 00:45:54.239 +examples I was able to to understand + +00:45:54.240 --> 00:45:55.159 +some of the... + +00:45:55.160 --> 00:45:58.079 +of these things here that are + +00:45:58.080 --> 00:46:00.239 +described here in the quick + +00:46:00.240 --> 00:46:04.719 +reference - but not all. + +00:46:04.720 --> 00:46:11.279 +So, I wasn't able to use lpegrex + +00:46:11.280 --> 00:46:14.279 +by itself, because some things didn't + +00:46:14.280 --> 00:46:16.199 +make much sense, and I decided to + +00:46:16.200 --> 00:46:18.759 +reimplement it in my own style, + +00:46:18.760 --> 00:46:23.679 +because that would be a way to map... + +00:46:23.680 --> 00:46:26.839 +to at the very least map what I had + +00:46:26.840 --> 00:46:29.559 +understood and what I didn't, learn + +00:46:29.560 --> 00:46:32.999 +one feature at a time, do comparisons, and + +00:46:33.000 --> 00:46:35.319 +so on. + +00:46:35.320 --> 00:46:38.799 +Here I pointed to two features of lpeg... + +00:46:38.800 --> 00:46:41.679 +in one I said "Oh, great! This thing can + +00:46:41.680 --> 00:46:44.319 +be used to to define grammars, even + +00:46:44.320 --> 00:46:45.959 +recursive grammars", and so on... + +00:46:45.960 --> 00:46:49.759 +and this is an "Oh, no!" feature - one + +00:46:49.760 --> 00:46:51.759 +thing that didn't make any sense at all... + +00:46:51.760 --> 00:46:56.439 +group captures. One thing that I did to + +00:46:56.440 --> 00:46:59.039 +understand group captures was to + +00:46:59.040 --> 00:47:02.319 +represent them as diagrams. Of course in + +00:47:02.320 --> 00:47:05.359 +the beginning I was drawing these + +00:47:05.360 --> 00:47:08.919 +diagrams by hand, but then I realized + +00:47:08.920 --> 00:47:11.559 +that I could use the bits of lpeg + +00:47:11.560 --> 00:47:14.759 +that I already knew to build a grammar + +00:47:14.760 --> 00:47:17.479 +that would parse a little language and + +00:47:17.480 --> 00:47:20.999 +generate these diagrams in LaTeX, and I was + +00:47:21.000 --> 00:47:21.919 +able to make this. + +00:47:21.920 --> 00:47:25.279 +In this diagram here + +00:47:25.280 --> 00:47:30.719 +this thing above the arrow is Lua code... + +00:47:30.720 --> 00:47:33.759 +a piece of Lua code that + +00:47:33.760 --> 00:47:37.119 +specifies an lpeg pattern... this + +00:47:37.120 --> 00:47:39.559 +thing here at the top is the string that + +00:47:39.560 --> 00:47:43.039 +is being matched, and the things below + +00:47:43.040 --> 00:47:46.599 +the underbraces are the captures that + +00:47:46.600 --> 00:47:50.639 +each thing... sorry, that each thing + +00:47:50.640 --> 00:47:51.319 +captures. + +00:47:51.320 --> 00:47:58.479 +For example, this underbrace here + +00:47:58.480 --> 00:48:00.279 +corresponds to this pattern here, + +00:48:00.280 --> 00:48:02.879 +that parses a single character but + +00:48:02.880 --> 00:48:05.559 +doesn't return any captures, this thing + +00:48:05.560 --> 00:48:08.119 +here parses a single "b" and doesn't + +00:48:08.120 --> 00:48:11.239 +return any captures, this thing here + +00:48:11.240 --> 00:48:14.399 +parses a single character and captures + +00:48:14.400 --> 00:48:16.879 +it, and this thing here parses the + +00:48:16.880 --> 00:48:21.319 +character "d" and captures it... and this + +00:48:21.320 --> 00:48:24.439 +other thing here transforms this + +00:48:24.440 --> 00:48:27.279 +pattern into another pattern... + +00:48:27.280 --> 00:48:33.119 +returns first a capture with all + +00:48:33.120 --> 00:48:35.079 +the string that was parsed by this + +00:48:35.080 --> 00:48:37.399 +pattern here, and then all the captures + +00:48:37.400 --> 00:48:41.079 +returned by this thing here before + +00:48:41.080 --> 00:48:42.959 +the ":". + +00:48:42.960 --> 00:48:45.479 +So, this was a way to build + +00:48:45.480 --> 00:48:48.599 +concrete examples for things that the + +00:48:48.600 --> 00:48:52.159 +lpag manual was explaining in a very terse + +00:48:52.160 --> 00:48:55.799 +way, and it worked for me - some things + +00:48:55.800 --> 00:48:56.999 +that were very + +00:48:57.000 --> 00:48:59.839 +mysterious started to make sense, and I + +00:48:59.840 --> 00:49:03.199 +started to have intelligent questions + +00:49:03.200 --> 00:49:06.079 +to ask in the mailing list. + +00:49:06.080 --> 00:49:10.959 +And with that I was able to + +00:49:10.960 --> 00:49:12.959 +understand what are group captures, + +00:49:12.960 --> 00:49:17.879 +and group captures that receive a name... + +00:49:17.880 --> 00:49:22.719 +Well, let me explain what this does. + +00:49:22.720 --> 00:49:27.119 +This thing here captures... sorry, parses + +00:49:27.120 --> 00:49:29.359 +the empty string and returns this as a + +00:49:29.360 --> 00:49:32.959 +constant... so, this is something that + +00:49:32.960 --> 00:49:35.799 +doesn't exist in regular expressions... + +00:49:35.800 --> 00:49:38.639 +it parses nothing and + +00:49:38.640 --> 00:49:41.839 +returns this as a capture... then this + +00:49:41.840 --> 00:49:44.599 +thing here returns these two + +00:49:44.600 --> 00:49:47.159 +constants here, and parses the empty + +00:49:47.160 --> 00:49:51.279 +string, and this thing here converts + +00:49:51.280 --> 00:49:54.159 +the results of this thing here into a + +00:49:54.160 --> 00:49:57.639 +group capture, and stores it in the label + +00:49:57.640 --> 00:50:03.279 +"d"... and then here's another constant + +00:50:03.280 --> 00:50:03.719 +capture. + +NOTE Building lists + +00:50:03.720 --> 00:50:05.679 +And I realized that these things + +00:50:05.680 --> 00:50:08.599 +here were similar to how Lua + +00:50:08.600 --> 00:50:09.839 +specifies building lists... + +00:50:09.840 --> 00:50:16.239 +when we build... sorry, tables. When + +00:50:16.240 --> 00:50:18.759 +we build a table, and we say that the + +00:50:18.760 --> 00:50:21.879 +first element of the table is here, this + +00:50:21.880 --> 00:50:23.559 +element is put at the end of the table... + +00:50:23.560 --> 00:50:29.399 +when after the that would say d=42... + +00:50:29.400 --> 00:50:31.199 +we are putting the 42 + +00:50:31.200 --> 00:50:34.559 +in the the slot whose key is "d". + +00:50:34.560 --> 00:50:38.999 +This was happening with lpeg captures, + +00:50:39.000 --> 00:50:43.359 +but there was something very strange... + +00:50:43.360 --> 00:50:46.199 +these group captures could hold + +00:50:46.200 --> 00:50:49.199 +more than one capture - more than one + +00:50:49.200 --> 00:50:51.759 +value... so there was something between + +00:50:51.760 --> 00:50:58.039 +lists and tables. I started to use this + +00:50:58.040 --> 00:51:00.479 +notation to... + +00:51:00.480 --> 00:51:04.959 +explain in my notation what they + +00:51:04.960 --> 00:51:08.159 +were doing... many things started + +00:51:08.160 --> 00:51:10.239 +to make sense, many mysterious + +00:51:10.240 --> 00:51:12.879 +sentences in the manual started to + +00:51:12.880 --> 00:51:14.439 +make sense... but some didn't... + +00:51:14.440 --> 00:51:19.679 +but at least I was able to send + +00:51:19.680 --> 00:51:22.319 +some intelligent questions to the + +00:51:22.320 --> 00:51:25.199 +mailing lis,t and the author of Lua and + +00:51:25.200 --> 00:51:27.359 +lpeg answered some of them... + +00:51:27.360 --> 00:51:31.519 +he was not very happy about my + +00:51:31.520 --> 00:51:34.959 +questions - he... told me that those + +00:51:34.960 --> 00:51:37.679 +diagrams were a waste of time, the + +00:51:37.680 --> 00:51:40.559 +manual was perfectly clear, and so on... + +00:51:40.560 --> 00:51:44.919 +whatever - but I was able to... + +00:51:44.920 --> 00:51:48.879 +so, it was weird, but I was able to + +00:51:48.880 --> 00:51:51.799 +understand lots of things from his + +00:51:51.800 --> 00:51:56.519 +answers. This is a copy of one of + +00:51:56.520 --> 00:51:58.239 +my messages, then there's another one, + +00:51:58.240 --> 00:52:01.239 +another one, some of them had diagrams... + +00:52:01.240 --> 00:52:04.359 +then he complained about these diagrams, + +00:52:04.360 --> 00:52:08.439 +he said that these things here, that look + +00:52:08.440 --> 00:52:11.119 +like table constructors, "do not exist"... + +00:52:11.120 --> 00:52:17.199 +whatever... anyway, once I understood + +00:52:17.200 --> 00:52:20.679 +group captures many features + +00:52:20.680 --> 00:52:23.359 +were very easy to understand + +00:52:23.360 --> 00:52:26.039 +and I started to be able to use lpeg to + +00:52:26.040 --> 00:52:28.159 +to build some very interesting things... + +00:52:28.160 --> 00:52:33.039 +I was able to reproduce some + +00:52:33.040 --> 00:52:36.359 +of the features that I saw in lpegrex - + +00:52:36.360 --> 00:52:41.079 +remember that this... where is that? + +00:52:41.080 --> 00:52:46.119 +this is the syntax of Lua... here - + +00:52:46.120 --> 00:52:48.959 +I was able to understand + +00:52:48.960 --> 00:52:52.479 +how these things here were translated to + +00:52:52.480 --> 00:52:55.359 +lpeg code... to lpeg patterns + +00:52:55.360 --> 00:52:58.239 +by using group captures in a certain + +00:52:58.240 --> 00:53:03.039 +way... I was able to implement them + +00:53:03.040 --> 00:53:04.759 +in ELpeg1.lua... + +00:53:04.760 --> 00:53:08.719 +and after some time I was able to use + +00:53:08.720 --> 00:53:12.879 +ELpeg1.lua to build grammars that + +00:53:12.880 --> 00:53:14.159 +were able to parse + +00:53:14.160 --> 00:53:18.679 +arithmetical expressions with the + +00:53:18.680 --> 00:53:20.959 +right precedence... and here's an example + +00:53:20.960 --> 00:53:23.319 +in which I built the grammar step by step... + +00:53:23.320 --> 00:53:29.239 +and I test the current grammar, and I + +00:53:29.240 --> 00:53:35.079 +replace a bit, and then I test the new + +00:53:35.080 --> 00:53:36.599 +grammar and so on... + +00:53:36.600 --> 00:53:39.079 +and you can see that the result is + +00:53:39.080 --> 00:53:43.359 +always a tree that is drawn in a + +00:53:43.360 --> 00:53:44.239 +nice two dimensional way... + +00:53:44.240 --> 00:53:48.919 +At this point these powers here + +00:53:48.920 --> 00:53:50.559 +are returned as a list, + +00:53:50.560 --> 00:53:53.119 +as an operation "pow" + +00:53:53.120 --> 00:53:57.559 +with several arguments, here... and then + +00:53:57.560 --> 00:54:00.519 +I apply a kind of parsing combinator, + +00:54:00.520 --> 00:54:03.719 +here... that transforms these trees into + +00:54:03.720 --> 00:54:08.199 +other trees and with these combinators + +00:54:08.200 --> 00:54:12.199 +here I can specify that the "^" is + +00:54:12.200 --> 00:54:14.639 +associative in a certain direction... + +00:54:14.640 --> 00:54:17.519 +that the "/" is associative in + +00:54:17.520 --> 00:54:20.119 +another direction... the "-" uses + +00:54:20.120 --> 00:54:23.079 +the same direction as a the "/", + +00:54:23.080 --> 00:54:26.079 +and so on... and they have the + +00:54:26.080 --> 00:54:29.679 +right precedences. + +00:54:29.680 --> 00:54:34.559 +So, here are the tests... + +00:54:34.560 --> 00:54:38.119 +here is my file ELpeg1.lua... it has + +00:54:38.120 --> 00:54:41.719 +several classes, each class has tests + +00:54:41.720 --> 00:54:42.279 +after it... + +00:54:42.280 --> 00:54:46.239 +I was able to implement something + +00:54:46.240 --> 00:54:50.519 +that lpegrex has, that is called + +00:54:50.520 --> 00:54:53.519 +"keywords", that is very useful for parsing + +00:54:53.520 --> 00:54:56.479 +programs in programming languages... + +00:54:56.480 --> 00:54:59.439 +I was able to implement something + +00:54:59.440 --> 00:55:02.639 +similar to the debugger... to the + +00:55:02.640 --> 00:55:07.999 +lpeg debugger lpeg uses... I was + +00:55:08.000 --> 00:55:11.399 +frustrated by some limitations of + +00:55:11.400 --> 00:55:16.839 +the lpeg debugger, and I implemented + +00:55:16.840 --> 00:55:23.439 +my own that is, uh... much better!... + +00:55:23.440 --> 00:55:24.759 +Let me show something else... I was + +00:55:24.760 --> 00:55:27.119 +able to translate a good part of the + +00:55:27.120 --> 00:55:33.039 +Lua parser, here, to ELpeg1.lua... I haven't + +00:55:33.040 --> 00:55:38.399 +finished yet, but I have most of the + +00:55:38.400 --> 00:55:39.719 +the translation here... + +00:55:39.720 --> 00:55:47.279 +and after having all that I was able to + +00:55:47.280 --> 00:55:50.319 +build other grammars very quickly... + +00:55:50.320 --> 00:55:55.239 +writing new parsers finally became fun. + +00:55:55.240 --> 00:55:58.719 +And here's one example that I showed in the + +00:55:58.720 --> 00:56:00.639 +beginning. + +00:56:00.640 --> 00:56:05.799 +If I remember correctly... + +00:56:05.800 --> 00:56:10.639 +I took a figure from the Wikipedia... + +00:56:10.640 --> 00:56:12.439 +I don't have its link now... + +00:56:12.440 --> 00:56:17.079 +but I specified a grammar that parses + +00:56:17.080 --> 00:56:20.119 +exactly the example that appears + +00:56:20.120 --> 00:56:20.839 +in the Wikipedia... + +00:56:20.840 --> 00:56:24.679 +so, with my grammar, considering that + +00:56:24.680 --> 00:56:28.719 +the top level entry is "Stmt", when I + +00:56:28.720 --> 00:56:30.679 +parse this string here + +00:56:30.680 --> 00:56:36.599 +the result is this tree... + +00:56:36.600 --> 00:56:41.119 +and I can do some operations on that, + +00:56:41.120 --> 00:56:44.039 +I can define how this thing is to be + +00:56:44.040 --> 00:56:45.639 +converted into LaTeX, + +00:56:45.640 --> 00:56:49.399 +I can define other operations + +00:56:49.400 --> 00:56:52.999 +that convert trees into other trees, and + +00:56:53.000 --> 00:56:54.879 +here are some tests of these operations... + +00:56:54.880 --> 00:57:00.359 +This is what I showed in the beginning... + +00:57:00.360 --> 00:57:02.759 +I'm not going to explain all the details + +00:57:02.760 --> 00:57:03.999 +of this thing now... + +00:57:04.000 --> 00:57:09.199 +this :show() converts this thing + +00:57:09.200 --> 00:57:11.919 +into LaTeX in the way specified by these + +00:57:11.920 --> 00:57:16.159 +instructions here, that says that... + +00:57:16.160 --> 00:57:25.239 +well, whatever... + +00:57:25.240 --> 00:57:32.959 +and here's the result - the LaTeXed result... + +00:57:32.960 --> 00:57:41.759 +and these diagrams here are generated by + +00:57:41.760 --> 00:57:46.719 +this file here, that defines a simple + +00:57:46.720 --> 00:57:48.479 +grammar that parses this thing here, + +00:57:48.480 --> 00:57:51.999 +and then LaTeXes it in a certain way, and + +00:57:52.000 --> 00:57:56.399 +and also tests to check if this code here... + +00:57:56.400 --> 00:58:01.999 +this Lua code that generates an lpeg grammar... + +00:58:02.000 --> 00:58:05.799 +parses this subject here and + +00:58:05.800 --> 00:58:08.599 +returns the expected result... + +00:58:08.600 --> 00:58:12.239 +So: this is the code that I + +00:58:12.240 --> 00:58:16.719 +wanted to show. I wanted to show many + +00:58:16.720 --> 00:58:19.919 +more things but I wasn't able to prepare + +00:58:19.920 --> 00:58:23.919 +them before the conference... and I hope + +00:58:23.920 --> 00:58:27.519 +that soon - for some value of "soon" - + +00:58:27.520 --> 00:58:30.399 +I'll be able to create REPL-based + +00:58:30.400 --> 00:58:33.919 +tutorials for lpeg, Re, and ELpeg1.lua... + +00:58:33.920 --> 00:58:36.319 +where lpeg is something very famous, + +00:58:36.320 --> 00:58:39.199 +Re is a module of lpeg... + +00:58:39.200 --> 00:58:42.399 +I could also do something like this + +00:58:42.400 --> 00:58:47.799 +for lpegrex... and ELpeg1.lua is + +00:58:47.800 --> 00:58:51.159 +the thing that I wrote, the one that + +00:58:51.160 --> 00:58:56.799 +has test in comments, and the tests + +00:58:56.800 --> 00:58:59.519 +usually generate trees, and sometimes + +00:58:59.520 --> 00:59:00.879 +they generate TeX code. + +00:59:00.880 --> 00:59:04.959 +Yeah, so that's it! I wanted to + +00:59:04.960 --> 00:59:07.159 +present much more but I wasn't able to + +00:59:07.160 --> 00:59:10.480 +prepare it... so: sorry, thanks, bye! =) |