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# Transcript
[[!template new="1" text="""Hi everyone!""" start="00:00:00.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Welcome to our talk on Parallel Text Replacement.""" start="00:00:01.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""My name is Lovro, and I'll be telling you about an""" start="00:00:04.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""interesting problem that my friend Valentino and I""" start="00:00:07.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""set out to solve one afternoon.""" start="00:00:09.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We will describe the problem, take a look at some""" start="00:00:11.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""of the existing work and then present our solution.""" start="00:00:13.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Afterwards, we will show some demos and conclude""" start="00:00:16.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""with a quick overview of the implementation.""" start="00:00:19.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Let's get straight into it!""" start="00:00:21.520" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Here is a problem that most of us have dealt with""" start="00:00:23.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""at some point.""" start="00:00:25.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Assume we have a piece of code such as the following.""" start="00:00:27.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We use a code example here, but in general what we're""" start="00:00:29.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""about to discuss can be applied to any piece of text.""" start="00:00:32.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""After a bit of thinking, we decide that the names of""" start="00:00:35.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the two variables, "foo" and "bar", should actually be""" start="00:00:37.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""swapped.""" start="00:00:39.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""That is, "foo" should be replaced with "bar", and "bar"""" start="00:00:40.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""should be replaced with "foo".""" start="00:00:43.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The question is: what is a good way to achieve this?""" start="00:00:45.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We could perform the edits manually if the code is""" start="00:00:49.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""small enough, and we might even be done reasonably""" start="00:00:51.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""quickly.""" start="00:00:53.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""However, consider two things.""" start="00:00:54.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Imagine the usual case where there's just too much""" start="00:00:56.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""code to edit by hand.""" start="00:00:58.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We have no other option than to automate the task.""" start="00:01:00.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""More importantly though, we have a whole programmable""" start="00:01:03.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""text editor right at our fingertips.""" start="00:01:06.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We should object to doing things that the computer""" start="00:01:08.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""can do for us.""" start="00:01:10.280" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""So, one way to automate it is by using our old friend""" start="00:01:12.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""query-replace (M-%) multiple times in a sequence.""" start="00:01:15.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We first do a pass where we replace "foo" with "bar",""" start="00:01:19.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""then we do another pass where we replace "bar" with "foo".""" start="00:01:22.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""But that's clearly not right.""" start="00:01:25.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We all know that this naive multi-pass approach""" start="00:01:26.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""doesn't work because it results in interference""" start="00:01:29.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""between the two replacements.""" start="00:01:31.560" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Instead, we have to be a bit more clever.""" start="00:01:34.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We should first replace "foo" with a temporary string,""" start="00:01:36.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""in this case "oof", that we will call a "token".""" start="00:01:39.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""To avoid interference, we must be careful to ensure""" start="00:01:42.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""that the token does not contain whatever we're about""" start="00:01:45.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to replace next.""" start="00:01:48.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Then we do a second pass to replace "bar" with "foo",""" start="00:01:49.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and finally a third pass to replace the token with "bar".""" start="00:01:52.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This gives us the result we want.""" start="00:01:56.080" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Putting the implementation aside for a moment, this style""" start="00:01:57.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""of text replacement, where we replace multiple sources""" start="00:02:01.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""with their targets, without running into interference""" start="00:02:05.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""issues between replacement pairs, is what we call""" start="00:02:09.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""a "parallel replacement".""" start="00:02:11.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This is the essence of the problem we're trying to solve.""" start="00:02:12.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The examples with swapping that we've shown so far""" start="00:02:16.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""are really just one of the many use cases that are""" start="00:02:18.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""supported by a general parallel replacement utility.""" start="00:02:21.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""To avoid confusion, let us clarify that the word "parallel"""" start="00:02:25.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""is not in reference to hardware parallelization, but""" start="00:02:28.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""rather comes from analogy with the Lisp let operator,""" start="00:02:31.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""where the bindings of variables are performed in parallel,""" start="00:02:34.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""rather than sequentially as in let*.""" start="00:02:38.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Parallel in this context means that none of the bindings""" start="00:02:40.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""are in scope within any of the initial value forms.""" start="00:02:43.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""In other words, just like a let's initialization form""" start="00:02:46.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""cannot refer to any of the earlier bindings, a""" start="00:02:50.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replacement pair's source should not be able to replace""" start="00:02:53.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the previously substituted targets of any other pair.""" start="00:02:56.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This is what we mean by "no interference".""" start="00:03:00.200" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""However, manually invoking multiple carefully chosen""" start="00:03:04.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""query-replace commands gets old very quickly.""" start="00:03:08.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Say we scaled up the problem and wanted to perform n""" start="00:03:11.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""swaps instead of just two, e.g. to swap, or rather,""" start="00:03:14.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""rotate, "foo" to "bar", "bar" to "baz", "baz" to "quux"""" start="00:03:18.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and "quux" to "foo".""" start="00:03:22.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We would first have to perform n - 1 additional""" start="00:03:23.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replacements to introduce the necessary tokens,""" start="00:03:26.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""effectively doubling the number of steps.""" start="00:03:29.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Even if we tried to automate this, think about what""" start="00:03:32.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""tokens the code would have to generate if we had no""" start="00:03:34.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""prior knowledge of the replacement pairs given by the""" start="00:03:37.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""user.""" start="00:03:40.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We would have to program defensively and use long""" start="00:03:41.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""randomly-generated strings that, one, hopefully do""" start="00:03:44.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""not interfere with any of the replacement pairs,""" start="00:03:47.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and two, might slow down the search if they're overly long.""" start="00:03:50.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Can we do better?""" start="00:03:53.480" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Yes we can!""" start="00:03:55.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We can actually perform just a single pass.""" start="00:03:56.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The trick is to alternate between the replacement""" start="00:03:59.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""pairs, replacing whichever source occurs the earliest,""" start="00:04:02.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and making sure to continue scanning after the end""" start="00:04:06.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""of the substituted target in order to avoid interference.""" start="00:04:08.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This interleaving of replacements is not something""" start="00:04:12.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""that's easy to do by hand with query-replace.""" start="00:04:14.520" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Since this is Emacs we're talking about, of course""" start="00:04:18.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""there already exist solutions that implement this idea.""" start="00:04:20.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Here are few that we could find.""" start="00:04:23.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The EmacsWiki has a page dedicated to this problem.""" start="00:04:25.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Stack Overflow has an old post where a couple of""" start="00:04:28.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""users provided their solutions.""" start="00:04:31.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Mastering Emacs also gives a method along with other""" start="00:04:33.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""interesting query-replace-regexp (C-M-%) patterns.""" start="00:04:36.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""More recently, Tony Zorman made a blogpost providing""" start="00:04:39.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""a solution with an interface based on query-replace.""" start="00:04:42.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""I encourage you to take a look at these solutions if""" start="00:04:45.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""you're interested in the details.""" start="00:04:47.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""But while a step in the right direction, these solutions""" start="00:04:50.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""are not satisfactory because they all lack one or""" start="00:04:53.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""more of the following.""" start="00:04:55.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""One, they are not completely automated and require""" start="00:04:56.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the user to come up with a relatively complicated""" start="00:05:00.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and verbose query-replace-regexp invocation.""" start="00:05:02.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Two, they are restricted to performing only 2-element""" start="00:05:06.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""swaps rather than general parallel replacements.""" start="00:05:09.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Three, they don't provide any sort of interactivity""" start="00:05:12.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""during replacement and instead perform it in one shot.""" start="00:05:15.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Four, they don't attempt to integrate with the familiar""" start="00:05:18.620" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""query-replace interface, which supports skipping, undo,""" start="00:05:21.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""history and more advanced features like Lisp expressions""" start="00:05:25.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and recursive query edits.""" start="00:05:28.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Most importantly however, five, none of them were""" start="00:05:30.700" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""designed with regular expressions in mind and instead""" start="00:05:33.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""only ever consider literal strings.""" start="00:05:36.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""In fact, the only one that comes close is the""" start="00:05:39.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""half-automated solution that invokes query-replace-regexp""" start="00:05:43.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""with a specially crafted replacement.""" start="00:05:46.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""As an example, here's how you would use this technique""" start="00:05:48.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to perform a 3-element parallel regex replacement.""" start="00:05:51.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""It uses the backslash-comma Lisp expression feature""" start="00:05:54.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""in order to choose the appropriate target to substitute.""" start="00:05:57.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Aside from being very clumsy and tedious to write out,""" start="00:06:01.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""this approach makes it really hard to use more complex""" start="00:06:03.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""regular expressions that make use of capture groups""" start="00:06:06.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""themselves.""" start="00:06:09.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This was the biggest limitation that we wanted""" start="00:06:10.800" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to get rid of and the main motivation for our work.""" start="00:06:12.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""So, as an alternative to the existing zoo of 80% solutions,""" start="00:06:15.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""we aim to provide a 100% solution, one that handles""" start="00:06:19.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""regexes and consolidates all of the existing ideas""" start="00:06:24.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""into a single package.""" start="00:06:27.120" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""We call it query-replace-parallel.""" start="00:06:29.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The package is free and open-source and can currently""" start="00:06:31.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""be found on GitHub under hokomo/query-replace-parallel.""" start="00:06:34.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The name is not yet finalized and we're open to any""" start="00:06:37.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""suggestions.""" start="00:06:40.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We hope to get it published on an Elisp""" start="00:06:41.503" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""package archive in the near future, but for now you""" start="00:06:43.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""can just download and load the main Elisp file manually.""" start="00:06:45.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""With all of that said, let's go through a few demos""" start="00:06:48.900" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to illustrate some use cases and see how to use the package.""" start="00:06:51.400" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Our first demo is a simple swap, like the one we""" start="00:06:55.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""showed at the beginning of the presentation.""" start="00:06:57.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This chunk of text is actually one of the tests""" start="00:06:59.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""from our package's code.""" start="00:07:02.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Assuming we have loaded the package, we can execute""" start="00:07:03.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the query-replace-parallel command, a parallel version""" start="00:07:06.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""of the standard query-replace.""" start="00:07:09.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This command works with literal strings and will""" start="00:07:11.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""ask for each source and target in turn.""" start="00:07:14.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Our goal is to replace "foo" with "bar"""" start="00:07:16.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and "bar" with "foo".""" start="00:07:21.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""After inputting our replacements, we terminate the""" start="00:07:24.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""prompt by pressing enter with empty input.""" start="00:07:27.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""At this point, everything functions the same as in""" start="00:07:29.860" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""a standard query-replace invocation.""" start="00:07:32.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The echo area shows the match and the replacement""" start="00:07:35.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""we're about to make.""" start="00:07:37.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We can perform replacements,""" start="00:07:38.703" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""undo them,""" start="00:07:43.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""skip them,""" start="00:07:46.503" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""execute them until the end,""" start="00:07:49.203" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and so on.""" start="00:07:50.240" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""The second demo shows our first regex use case.""" start="00:07:53.970" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Imagine we have the following LaTeX code.""" start="00:07:56.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We realize that we haven't been completely consistent""" start="00:07:58.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""in our use and naming of macros, so we decide to""" start="00:08:01.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""fix the problem.""" start="00:08:04.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This time we execute query-replace-parallel-regexp""" start="00:08:05.536" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""because we want to work with regex instead of literal""" start="00:08:08.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""strings.""" start="00:08:11.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We want to achieve two things.""" start="00:08:12.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""First, we want to wrap all usages of the variable n""" start="00:08:13.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""with the natvar macro.""" start="00:08:16.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Using the backslash-less-than and blackslash-greater-than""" start="00:08:18.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""constructs allows us to only match letters n not""" start="00:08:21.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""appearing as part of a larger word.""" start="00:08:23.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Second, we want to rename natvar to intvar because""" start="00:08:25.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the variables a, b and c are integers and not natural""" start="00:08:29.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""numbers.""" start="00:08:32.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We enter empty input to terminate the prompt and can""" start="00:08:33.300" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""now perform the replacements.""" start="00:08:35.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""There we go, the fixes are done and we didn't have""" start="00:08:42.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to think about in which order to apply them.""" start="00:08:44.480" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""We now take a look at a more complicated regex""" start="00:08:48.700" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""example to demonstrate that even advanced query-replace""" start="00:08:51.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""features are supported.""" start="00:08:53.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Each "foo" and "bar" in this example is followed by""" start="00:08:55.100" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""a number.""" start="00:08:57.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The goal is to not only swap "foo" and "bar", but""" start="00:08:58.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""also increase or decrease the corresponding number.""" start="00:09:01.380" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We first match "foo" and capture the number that""" start="00:09:03.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""follows it.""" start="00:09:06.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""For the target, we make use of the backslash-comma""" start="00:09:07.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Lisp expression feature in order to replace the""" start="00:09:10.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""match with "bar" followed by the number's successor.""" start="00:09:12.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We do the same thing for "bar", except that we""" start="00:09:15.540" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replace the number with its predecessor.""" start="00:09:17.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Performing the replacements, we can see how each""" start="00:09:27.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""number is incremented or decremented appropriately.""" start="00:09:29.120" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""We haven't covered it explicitly so some of you may""" start="00:09:36.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""be wondering how parallel replacement deals with""" start="00:09:38.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""overlapping matches and whether the order of the""" start="00:09:41.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replacement pairs is significant.""" start="00:09:43.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This demo will clarify the exact behavior.""" start="00:09:45.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The first example has the sources "watch" and "stopwatch".""" start="00:09:48.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Conceptually, the matches overlap, but the rule is""" start="00:09:57.500" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""that matches are always processed earliest first,""" start="00:10:00.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""regardless of their length or the ordering of the pairs.""" start="00:10:03.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Therefore it is "stopwatch" that gets replaced,""" start="00:10:06.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and not its substring "watch".""" start="00:10:09.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The second example uses the sources "watch" and "watchword".""" start="00:10:16.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Both of the matches now conceptually start at the same""" start="00:10:19.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""position.""" start="00:10:22.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""In situations like these the order of the pairs does""" start="00:10:23.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""matter, and ties are broken by prefering the pair that""" start="00:10:26.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""was entered first, which is behavior that is inherited""" start="00:10:29.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""from the Elisp regex engine.""" start="00:10:32.280" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""So, the substring "watch" in "watchword" is what gets""" start="00:10:34.460" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replaced in this case.""" start="00:10:37.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Situations where the order of the pairs is significant""" start="00:10:39.460" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""are not very common however, so the user generally""" start="00:10:41.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""doesn't have to worry about this edge case.""" start="00:10:44.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The order only matters when two or more sources""" start="00:10:46.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""share the same prefix, as in this example.""" start="00:10:49.960" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""The final demo tests the limits of the package and""" start="00:10:54.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""shows that it fully integrates with query-replace.""" start="00:10:56.960" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""It is really just for fun and can even serve as a""" start="00:10:59.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""small Emacs brainteaser.""" start="00:11:03.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""See if you can keep up!""" start="00:11:04.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We open a directory and enter Writable Dired mode""" start="00:11:06.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""in order to rename the directories "foo" and "bar".""" start="00:11:09.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Instead of doing it quickly by hand, we decide to""" start="00:11:11.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""show off and use query-replace-parallel-regexp.""" start="00:11:14.760" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We enter our pairs and make use of the""" start="00:11:17.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""backslash-question-mark query edit feature.""" start="00:11:20.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Now whenever we perform a replacement, the query""" start="00:11:25.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""edit makes Emacs stop and prompt us for additional""" start="00:11:27.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""input to use as the target.""" start="00:11:30.840" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We confirm the renames and now enter the "bar-lib"""" start="00:11:36.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""directory in order to perform the same kind of""" start="00:11:39.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""replacement on "baz" and "quux".""" start="00:11:42.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Rather than save time, we decide to be extra lazy""" start="00:11:44.500" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and take the long route.""" start="00:11:47.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We recall the first pair and initiate a recursive""" start="00:11:48.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""invocation of query-replace-parallel-regexp.""" start="00:11:52.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We are now replacing the replacement.""" start="00:11:54.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We apply our fixes and then do the same thing again""" start="00:12:01.020" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""with the second pair.""" start="00:12:04.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Recall and recurse.""" start="00:12:05.970" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We confirm the prompt and finally rename our directories.""" start="00:12:16.300" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Wow, that really paid off.""" start="00:12:25.360" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""Before we finish, a few quick words about the""" start="00:12:29.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""implementation for the curious.""" start="00:12:31.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Both query-replace-parallel and query-replace-parallel-regexp""" start="00:12:33.300" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""delegate to the complex perform-replace function""" start="00:12:36.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""which is the workhorse of query-replace's interactive""" start="00:12:39.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""mechanism.""" start="00:12:41.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The way we achieve multiple interleaved replacements""" start="00:12:43.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""is by providing perform-replace with a big "matcher regex"""" start="00:12:45.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and a special replacement function.""" start="00:12:49.120" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Essentially, a complex parallel replacement like this""" start="00:12:50.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""is transformed into a standard replacement like this.""" start="00:12:54.400" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This is similar to the trick shown earlier in the""" start="00:12:57.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""presentation.""" start="00:13:00.200" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Each source is put in its own capture group to allow""" start="00:13:00.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""the replacement function to determine which one matched""" start="00:13:03.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""and return the appropriate target.""" start="00:13:06.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""However, we now take care to support arbitrary""" start="00:13:08.980" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""regular expressions as sources.""" start="00:13:11.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We achieve this by converting each source regex into""" start="00:13:13.480" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""an equivalent one for which we can guarantee that its""" start="00:13:17.080" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""capture groups will not clash with our matcher regex.""" start="00:13:19.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Information about this conversion is stored, and""" start="00:13:22.920" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""once the replacement function is called it has""" start="00:13:26.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""enough data to apply the replacement from the""" start="00:13:28.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""viewpoint of the original regex.""" start="00:13:30.360" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""The regex transformation is reliable because it""" start="00:13:32.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""uses the rx library, allowing us to treat regexes""" start="00:13:35.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""as s-expressions and avoid any nasty manual parsing.""" start="00:13:38.520" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""In fact, rx itself is based on one of Olin Shivers'""" start="00:13:42.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""100% solutions:""" start="00:13:46.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""SRE, or the S-expression regex notation.""" start="00:13:48.436" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""We all stand on the shoulders of many giants, so""" start="00:13:51.320" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""let's strive to design good solutions that we can""" start="00:13:54.440" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""all benefit from, many years into the future!""" start="00:13:56.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Finally, because query-replace's core is not completely""" start="00:13:59.240" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""customizable, we did have to sprinkle in some advice""" start="00:14:03.000" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""to get certain things working.""" start="00:14:06.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""This concerns only minor cosmetic fixes and not the""" start="00:14:07.600" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""core replacement functionality, but we have nontheless""" start="00:14:11.160" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""tried to do it in the simplest and least intrusive way""" start="00:14:14.040" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""possible.""" start="00:14:16.680" video="mainVideo-parallel" id="subtitle"]]
[[!template new="1" text="""In conclusion, go download and play with the package.""" start="00:14:18.740" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Even if you're not performing overlapping replacements,""" start="00:14:21.680" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""you can still use query-replace-parallel for the""" start="00:14:24.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""peace of mind knowing that things won't go wrong if""" start="00:14:26.880" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""you perform more than one replacement at a time.""" start="00:14:29.720" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Feel free to let us know about any interesting or""" start="00:14:32.460" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""crazy use cases you might come up with, as well as""" start="00:14:34.640" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""improvements or bugs that make it only a 99% solution.""" start="00:14:37.560" video="mainVideo-parallel" id="subtitle"]]
[[!template text="""Thanks for listening and have a great EmacsConf!""" start="00:14:40.640" video="mainVideo-parallel" id="subtitle"]]
Questions or comments? Please e-mail [hokomo@disroot.org](mailto:hokomo@disroot.org?subject=Comment%20for%20EmacsConf%202022%20parallel%3A%20Parallel%20text%20replacement)
<!-- End of emacsconf-publish-after-page -->
