Irreal

Protesilaos Stavrou (Prot) has a new heroic video. Heroic because it undertakes to describe the mechanism for controlling the placement of buffers. That is, where in the display environment should a buffer be displayed. That mechanism is complex so describing it usefully is a significant task.

For most of us, most of the time, the default behavior is fine but sometimes we would prefer something else to happen. This is Emacs so of course we can have it our way but even I was surprised at the level of control the user has.

The basic mechanism is an alist called display-buffer-alist. Prot describes this list as having entries of the form

;; ( BUFFER-MATCHING-RULE
;;   LIST-OF-DISPLAY-BUFFER-FUNCTIONS
;;   OPTIONAL-PARAMETERS)

The BUFFER-MATCHING-RULE is a regular expression or more complex expression that selects the buffers to which the LIST-OF-DISPLAY-BUFFER-FUNCTIONS and OPTIONAL-PARAMETERS should apply. Those functions and parameters can be selected from a very rich set and give very fine control over the buffer placement.

You’re going to have to watch Prot’s video for more details and even he doesn’t cover the full list of possibilities. He provides a link to his configuration for display-buffer-alist that demonstrate some of the advanced features but if you’re really interested in this you’ll probably have to consult the documentation.

The video is 29 minutes, 51 seconds so schedule some time. The video is a bit complex so schedule your watching for a time that you can focus on its content.

Protesilaos Stavrou (Prot) has posted a nifty video on abbrev-mode. It turns out that there’s a lot more to it than you might have thought. Prot says that you can think of it as a lightweight alternative for yasnippet or something similar. My view is that if you’re already familiar with YASnippet you should just use that but if you aren’t familiar with it or just want something simpler, abbrev-mode may be just what you need.

As Prot shows, it’s pretty easy to set up a simple abbreviation: you simply call the define-abbrev function specifying the abbreviation and its expansion. But even in this simple case there are some nuances. You also have to specify the major mode the abbreviation will be active in. That can be global or it can be more specific. The modes form a hierarchy with global mode at the top, more specific modes (such as text-mode) next, and then derived modes (such as org-mode). Abbreviations for lower modes override the same abbreviation at higher levels so there’s a consistent inheritance mechanism.

That’s all there is to the simple case but Prot considers two more complicated cases. First, you can replace the expansion string with a function that will return the expansion value. Prot uses the example of a function that returns an ASCII representation of the current time.

Next, he considers the case of expanding something like :emojiX to the corresponding emoji. The problem here is that abbrev-mode will not recognize :emojiX as a word because of the colon. You can tell abbrev-mode to recognize such things by adjusting the regular expression it uses to recognize abbreviations.

Prot gives all the details in his video and there’s a copy of his scratch file at the link so you don’t have to worry about copying the things he does down. The video is 26 minutes, 22 seconds long so you’ll have to schedule some time. As usual with Prot’s videos, it’s a worthwhile investment.

If you’ve been around Irreal for a while, you know that I’m a hug fan of abo-abo’s Swiper/Ivy/Counsel package. Its minibuffer completion system means that if I can get anywhere near the name of a command I’m trying to run or a file I’m trying to open, Ivy will find it, usually with just a couple of keystrokes. Even for complicated names, its builtin easy regular expression engine can easily filter a huge list of candidates to just a few close matches.

It turns out that I’m not the only fan. Martin Fowler is a well known software engineer and author who is also a long time Emacs user. Among his favorite Emacs tools is the same Swiper/Ivy/Counsel package much beloved at Irreal.

He has a post describing his Ivy use and how it makes his work much easier. He does a good job of describing the regular expression engine that will translate a space into .* so that foo bar will match any (sub)string beginning will foo and ending with bar. Two spaces are mapped to a space so it’s really easy to write a regular expression that usually does the job without resorting to the full Kleene notation.

Another nice (optional) feature of Ivy is that it can ignore order so that foo bar will match both foo comes before bar and bar comes after foo. You can turn that on for a single instance or configure Ivy to always use it. Check out the post for the details if you’re interested.

If you want to see how Ivy can meet your completion needs, take a look at Fowler’s post.

Update [2024-02-07 Wed 15:43]: Consult → Counsel

Ruslan Bekenev has an interesting post that discusses which-function-mode. I was vaguely familiar with it before I read Bekenev’s post but never thought much about it. Bekenev, however, makes a good case for it. His use case is that he has long functions and deep Org trees and it’s nice to be able to see at a glance where he is.

Wait. What? Org trees? What do they have to do with functions? Probably nothing but the thing is that when which-function-mode is on, it does an excellent job of telling you were you are regardless of what object it’s dealing with. If you’re in an Org tree, it will tell you what subheading you’re in. If you’re in a code buffer it does a similarly good job. I tried it out in my init.el and besides functions, it identified setq, devar, define-key, use=package, and, doubtless, many other objects.

Bekenev says that it worked on most of the files he tried except for files containing HTML. Still, it seems pretty complete.

If you’re a good doobie and keep your functions short it may not do much for you and in any event, if you’re working in a function you’d better know what function it is. On the other hand, it’s easy to imagine searching for a variable and landing in the middle of a function and having no idea what function it is. It may, ironically, be more useful in Org files. Of course, that’s just my take and you may have a very different opinion.

In any event, which-function-mode is a handy thing to know about. Bekenev’s post is short and well worth a minute or two of your time. Check it out.

Update [2024-02-04 Sun]: Fixed link.

Emacs Elements has a very short video on a relatively unknown but extraordinarily useful command: iedit. It does basically the same job as multiple cursors but is builtin and a bit simpler. It’s less powerful than multiple cursors but is usually more than powerful enough for the job at hand. I use it all the time, usually in preference to commands like query-replace and its siblings.

The video is less than two minutes long so it doesn’t cover many of the nuances involved with iedit. The most important such nuance is what text is selected for editing. If you just place the cursor on some text, the selected text is basically what’s returned by thing-at-point. I often find that that is not what I want so I highlight the word (or extended text) that I’m interested in instead. Then, that text is selected as if by a substring match. On the other hand, that may not always do the right thing either so you should be familiar with both methods. You can also edit the regular expression by hand to get exactly what you want.

Another obscure but useful nuance is restricting the range of selection to the current function. You do that by by specifying a prefix of 0 to the command. There’s a fairly long description of how the command works in its document string so ts worthwhile calling Help for iedit to get the full story.

As I said, the video is very short—only 1 minute, 55 seconds—so it’s easy to fit in. Take a look at the video to get the general idea but you should definitely read the Doc entry too.

Protesilaos Stavrou (Prot) has a great video on nesting key maps. A nested key map is just what it sounds like: a key map inside another key map. What that means practically is that one key shortcut will lead to another key map of additional choices.

In theory it works just as you think it should but there are some nuances and it’s nice to have the whole thing explained in one place. Prot’s video uses keymap-set and defvar-keymap, which assume you’re using Emacs 29 or later but even if you aren’t the process is the same except that you have to use the older commands such as define-key and make-sparse-keymap.

You can watch the video to see how to set up nested key-maps but, as I say, it works just like you think it would. One of the non obvious things that the video explains is how to deal with describing the key maps in which-key. To see why this matters, type Ctrl+x and wait until which-key pops up. You’ll see a lot of entries that say +prefix but there’s no indication of what the resulting key map does. Prot shows how to configure which-key to give the key map a meaningful name. That alone is worth watching the video for.

The video is 23 minutes, 17 seconds long so plan accordingly but you really should find some time to watch this video. If you hate watching videos, at least take a look at the sample code at the link. It’s a nice précis of how to set up nested key maps and configure which-key.