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Why I Stopped Using an External Monitor 2023-03-03 For the longest time I’ve been using a Samsung 27” UHD monitor as my main display. This monitor was connected to my ThinkPad X260 (in clamshell mode) through the official Lenovo dock. It wasn’t a bad setup, but I have since changed my ways. Instead, I now only use the X260’s panel as my main display. Let me explain my reasoning… The Switch to Suckless Over the past year I switched away from a traditional desktop environment to a window manager - dwm to be specific. This also involved changing most of my daily software programs to utilize the full suckless “suite”. In doing so, the shift away from floating windows and virtualized desktops happened quickly. I continued to use my UHD monitor with this new environment but slowly started running into minor (yet still inconvenient) roadblocks: Tiled mode was not the most optimized for such a large monitor. I found myself defaulting into “floating” mode which defeats the purpose of a WM. The...
over a year ago

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Installing OpenBSD on Linveo KVM VPS

Installing OpenBSD on Linveo KVM VPS 2024-10-21 I recently came across an amazing deal for a VPS on Linveo. For just $15 a year they provide: AMD KVM 1GB 1024 MB RAM 1 CPU Core 25 GB NVMe SSD 2000 GB Bandwidth It’s a pretty great deal and I suggest you look more into it if you’re interested! But this post is more focused on setting up OpenBSD via the custom ISO option in the KVM dashboard. Linveo already provides several Linux OS options, along with FreeBSD by default (which is great!). Since there is no OpenBSD template we need to do things manually. Getting Started Once you have your initial VPS up and running, login to the main dashboard and navigate to the Media tab. Under CD/DVD-ROM you’ll want to click “Custom CD/DVD” and enter the direct link to the install76.iso: https://cdn.openbsd.org/pub/OpenBSD/7.6/amd64/install76.iso The "Media" tab of the Linveo Dashboard. Use the official ISO link and set the Boot Order to CD/DVD. Select “Insert”, then set your Boot Order to CD/DVD and click “Apply”. Once complete, Restart your server. Installing via VNC With the server rebooting, jump over to Options and click on “Browser VNC” to launch the web-based VNC client. From here we will boot into the OpenBSD installer and get things going! Follow the installer as you normally would when installing OpenBSD (if you’re unsure, I have a step-by-step walkthrough) until you reach the IPv4 selection. At this point you will want to input your servers IPv4 and IPv6 IPs found under your Network section of your dashboard. Next you will want to set the IPv6 route to first default listed option (not “none”). After that is complete, choose cd0 for your install media (don’t worry about http yet). Continue with the rest of the install (make users if desired, etc) until it tells you to reboot the machine. Go back to the Linveo Dashboard, switch your Boot Order back to “Harddrive” and reboot the machine directly. Booting into OpenBSD Load into the VNC client again. If you did everything correctly you should be greeted with the OpenBSD login prompt. There are a few tweaks we still need to make, so login as the root user. Remember how we installed our sets directly from the cd0? We’ll want to change that. Since we are running OpenBSD “virtually” through KVM, our target network interface will be vio0. Edit the /etc/hostname.vio0 file and add the following: dhcp !route add default <your_gateway_ip> The <your_gateway_ip> can be found under the Network tab of your dashboard. The next file we need to tweak is /etc/resolv.conf. Add the following to it: nameserver 8.8.8.8 nameserver 1.1.1.1 These nameservers are based on your selected IPs under the Resolvers section of Network in the Linveo dashboard. Change these as you see fit, so long as they match what you place in the resolve.conf file. Finally, the last file we need to edit is /etc/pf.conf. Like the others, add the following: pass out proto { tcp, udp } from any to any port 53 Final Stretch Now just reboot the server. Log back in as your desired user and everything should be working as expected! You can perform a simple test to check: ping openbsd.org This should work - meaning your network is up and running! Now you’re free to enjoy the beauty that is OpenBSD.

8 months ago 76 votes
Vertical Tabs in Safari

Vertical Tabs in Safari 2024-09-26 I use Firefox as my main browser (specifically the Nightly build) which has vertical tabs built-in. There are instances where I need to use Safari, such as debugging or testing iOS devices, and in those instances I prefer to have a similar experience to that of Firefox. Luckily, Apple has finally made it fairly straight forward to do so. Click the Sidebar icon in the top left of the Safari browser Right click and group your current tab(s) (I normally name mine something uninspired like “My Tabs” or simply “Tabs”) For an extra “clean look”, remove the horizontal tabs by right clicking the top bar, selected Customize Toolbar and dragging the tabs out When everything is set properly, you’ll have something that looks like this: One minor drawback is not having access to a direct URL input, since we have removed the horizontal tab bar altogether. Using a set of curated bookmarks could help avoid the need for direct input, along with setting our new tab page to DuckDuckGo or any other search engine.

9 months ago 79 votes
Build and Deploy Websites Automatically with Git

Build and Deploy Websites Automatically with Git 2024-09-20 I recently began the process of setting up my self-hosted1 cgit server as my main code forge. Updating repos via cgit on NearlyFreeSpeech on its own has been simple enough, but it lacked the “wow-factor” of having some sort of automated build process. I looked into a bunch of different tools that I could add to my workflow and automate deploying changes. The problem was they all seemed to be fairly bloated or overly complex for my needs. Then I realized I could simply use post-receive hooks which were already built-in to git! You can’t get more simple than that… So I thought it would be best to document my full process. These notes are more for my future self when I inevitably forget this, but hopefully others can benefit from it! Before We Begin This “tutorial” assumes that you already have a git server setup. It shouldn’t matter what kind of forge you’re using, so long as you have access to the hooks/ directory and have the ability to write a custom post-receive script. For my purposes I will be running standard git via the web through cgit, hosted on NearlyFreeSpeech (FreeBSD based). Overview Here is a quick rundown of what we plan to do: Write a custom post-receive script in the repo of our choice Build and deploy our project when a remote push to master is made Nothing crazy. Once you get the hang of things it’s really simple. Prepping Our Servers Before we get into the nitty-gritty, there are a few items we need to take care of first: Your main git repo needs ssh access to your web hosting (deploy) server. Make sure to add your public key and run a connection test first (before running the post-receive hook) in order to approve the “fingerprinting”. You will need to git clone your main git repo in a private/admin area of your deploy server. In the examples below, mine is cloned under /home/private/_deploys Once you do both of those tasks, continue with the rest of the article! The post-receive Script I will be using my own personal website as the main project for this example. My site is built with wruby, so the build instructions are specific to that generator. If you use Jekyll or something similar, you will need to tweak those commands for your own purposes. Head into your main git repo (not the cloned one on your deploy server), navigate under the hooks/ directory and create a new file named post-receive containing the following: #!/bin/bash # Get the branch that was pushed while read oldrev newrev ref do branch=$(echo $ref | cut -d/ -f3) if [ "$branch" == "master" ]; then echo "Deploying..." # Build on the remote server ssh user@deployserver.net << EOF set -e # Stop on any error cd /home/private/_deploys/btxx.org git pull origin master gem install 'kramdown:2.4.0' 'rss:0.3.0' make build rsync -a build/* ~/public/btxx.org/ EOF echo "Build synced to the deployment server." echo "Deployment complete." fi done Let’s break everything down. First we check if the branch being pushed to the remote server is master. Only if this is true do we proceed. (Feel free to change this if you prefer something like production or deploy) if [ "$branch" == "master" ]; then Then we ssh into the server (ie. deployserver.net) which will perform the build commands and also host these built files. ssh user@deployserver.net << EOF Setting set -e ensures that the script stops if any errors are triggered. set -e # Stop on any error Next, we navigate into the previously mentioned “private” directory, pull the latest changes from master, and run the required build commands (in this case installing gems and running make build) cd /home/private/_deploys/btxx.org git pull origin master gem install 'kramdown:2.4.0' 'rss:0.3.0' make build Finally, rsync is run to copy just the build directory to our public-facing site directory. rsync -a build/* ~/public/btxx.org/ With that saved and finished, be sure to give this file proper permissions: chmod +x post-receive That’s all there is to it! Time to Test! Now make changes to your main git project and push those up into master. You should see the post-receive commands printing out into your terminal successfully. Now check out your website to see the changes. Good stuff. Still Using sourcehut My go-to code forge was previously handled through sourcehut, which will now be used for mirroring my repos and handling mailing lists (since I don’t feel like hosting something like that myself - yet!). This switch over was nothing against sourcehut itself but more of a “I want to control all aspects of my projects” mentality. I hope this was helpful and please feel free to reach out with suggestions or improvements! By self-hosted I mean a NearlyFreeSpeech instance ↩

9 months ago 92 votes
Burning & Playing PS2 Games without a Modded Console

Burning & Playing PS2 Games without a Modded Console 2024-09-02 Important: I do not support pirating or obtaining illegal copies of video games. This process should only be used to copy your existing PS2 games for backup, in case of accidental damage to the original disc. Requirements Note: This tutorial is tailored towards macOS users, but most things should work similar on Windows or Linux. You will need: An official PS2 game disc (the one you wish to copy) A PS2 Slim console An Apple device with a optical DVD drive (or a portable USB DVD drive) Some time and a coffee! (or tea) Create an ISO Image of Your PS2 Disc: Insert your PS2 disc into your optical drive. Open Disk Utility (Applications > Utilities) In Disk Utility, select your PS2 disc from the sidebar Click on the File menu, then select New Image > Image from [Disc Name] Choose a destination to save the ISO file and select the format as DVD/CD Master Name your file and click Save. Disk Utility will create a .cdr file, which is essentially an ISO file Before we move on, we will need to convert that newly created cdr file into ISO. Navigate to the directory where the .cdr file is located and use the hdiutil command to convert the .cdr file to an ISO file: hdiutil convert yourfile.cdr -format UDTO -o yourfile.iso You’ll end up with a file named yourfile.iso.cdr. Rename it by removing the .cdr extension to make it an .iso file: mv yourfile.iso.cdr yourfile.iso Done and done. Getting Started For Mac and Linux users, you will need to install Wine in order to run the patcher: # macOS brew install wine-stable # Linux (Debian) apt install wine Clone & Run the Patcher Clone the FreeDVDBoot ESR Patcher: git clone https://git.sr.ht/~bt/fdvdb-esr Navigate to the cloned project folder: cd /path/to/fdvdb-esr The run the executable: wine FDVDB_ESR_Patcher.exe Now you need to select your previously cloned ISO file, use the default Payload setting and then click Patch!. After a few seconds your file should be patched. Burning Our ISO to DVD It’s time for the main event! Insert a blank DVD-R into your disc drive and mount it. Then right click on your patched ISO file and run “Burn Disk Image to Disc...". From here, you want to make sure you select the slowest write speed and enable verification. Once the file is written to the disc and verified (verification might fail - it is safe to ignore) you can remove the disc from the drive. Before Playing the Game Make sure you change the PS2 disc speed from Standard to Fast in the main “Browser” setting before you put the game into your console. After that, enjoy playing your cloned PS2 game!

10 months ago 67 votes
"This Key is Useless Now. Discard?"

“This Key is Useless Now. Discard?” 2024-08-28 The title of this article probably triggers nostalgic memories for old school Resident Evil veterans like myself. My personal favourite in the series (not that anyone asked) was the original, 1998 version of Resident Evil 2 (RE2). I believe that game stands the test of time and is very close to a masterpiece. The recent remake lost a lot of the charm and nuance that made the original so great, which is why I consistently fire up the PS1 version on my PS2 Slim. Resident Evil 2 (PS1) running on my PS2, hooked up to my Toshiba CRT TV. But the point of this post isn’t to gush over RE2. Instead I would like to discuss how well RE2 handled its interface and user experience across multiple in-game systems. HUD? What HUD? Just like the first Resident Evil that came before it, RE2 has no in-game HUD (heads-up display) to speak of. It’s just your playable character and the environment. No ammo-counters. No health bars. No “quest” markers. Nothing. This is how the game looks while you play. Zero HUD elements. The game does provide you with an inventory system, which holds your core items, weapons and notes you find along your journey. Opening up this sub-menu allows you to heal, reload weapons, combine objects or puzzle items, or read through previously collected documents. Not only is this more immersive (HUDs don’t exist for us in the real world, we need to look through our packs as well…) it also gets out of the way. The main inventory screen. Shows everything you need to know, only when you need it. (I can hear this screenshot...) I don’t need a visual element in the bottom corner showing me a list of “items” I can cycle through. I don’t want an ammo counter cluttering up my screen with information I only need to see in combat or while manually reloading. If those are pieces of information I need, I’ll explicitly open and look for it. Don’t make assumptions about what is important to me on screen. Capcom took this concept of less visual clutter even further in regards to maps and the character health status. Where We’re Going, We Don’t Need Roads Mini-Maps A great deal of newer games come pre-packaged with a mini-map on the main interface. In certain instances this works just fine, but most are 100% UI clutter. Something to add to the screen. I can only assume some devs believe it is “helpful”. Most times it’s simply a distraction. Thank goodness most games allow you to disable them. As for RE2, you collect maps throughout your adventure and, just like most other systems in the game, you need to consciously open the map menu to view them. You know, just like in real life. This creates a higher tension as well, since you need to constantly reference your map (on initial playthroughs) to figure out where the heck to go. You feel the pressure of someone frantically pulling out a physical map and scanning their surroundings. It also helps the player build a mental model in their head, thus providing even more of that sweet, sweet immersion. The map of the Raccoon City Police Station. No Pain, No Gain The game doesn’t display any health bar or player status information. In order to view your current status (symbolized by “Fine”, “Caution” or “Danger”) you need to open your inventory screen. From here you can heal yourself (if needed) and see the status type change in real-time. The "condition" health status. This is fine. But that isn’t the only way to visually see your current status. Here’s a scenario: you’re traveling down a hallway, turn a corner and run right into the arms of a zombie. She takes a couple good bites out of your neck before you push her aside. You unload some handgun rounds into her and down she goes. As you run over her body she reaches out and chomps on your leg as a final “goodbye”. You break free and move along but notice something different in your character’s movement - they’re holding their stomach and limping. Here we can see the character "Hunk" holding his stomach and limping, indicating an injury without the need for a custom HUD element. If this was your first time playing, most players would instinctively open the inventory menu, where their characters health is displayed, and (in this instance) be greeted with a “Caution” status. This is another example of subtle UX design. I don’t need to know the health status of my character until an action is required (in this example: healing). The health system is out of the way but not hidden. This keeps the focus on immersion, not baby-sitting the game’s interface. A Key to Every Lock Hey! This section is in reference to the title of the article. We made it! …But yes, discarding keys in RE2 is a subtle example of fantastic user experience. As a player, I know for certain this key is no longer needed. I can safely discard it and free up precious space from my inventory. There is also a sense of accomplishment, a feeling of “I’ve completed a task” or an internal checkbox being ticked. Progress has been made! Don’t overlook how powerful of a interaction this little text prompt is. Ask any veteran of the series and they will tell you this prompt is almost euphoric. The game's prompt asking if you'd like to discard a useless key. Perfection. Inspiring Greatness RE2 is certainly not the first or last game to implement these “minimal” game systems. A more “modern” example is Dead Space (DS), along with its very faithful remake. In DS the character’s health is displayed directly on the character model itself, and a similar inventory screen is used to manage items. An ammo-counter is visible but only when the player aims their weapon. Pretty great stuff and another masterpiece of survival horror. In Dead Space, the character's health bar is set as part of their spacesuit. The Point I guess my main takeaway is that designers and developers should try their best to keep user experience intuitive. I know that sounds extremely generic but it is a lot more complex than one might think. Try to be as direct as possible while remaining subtle. It’s a delicate balance but experiences like RE2 show us it is attainable. I’d love to talk more, but I have another play-through of RE2 to complete…

10 months ago 70 votes

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22 hours ago 4 votes
Get in losers, we're moving to Linux!

I've never seen so many developers curious about leaving the Mac and giving Linux a go. Something has really changed in the last few years. Maybe Linux just got better? Maybe powerful mini PCs made it easier? Maybe Apple just fumbled their relationship with developers one too many times? Maybe it's all of it. But whatever the reason, the vibe shift is noticeable. This is why the future is so hard to predict! People have been joking about "The Year of Linux on the Desktop" since the late 90s. Just like self-driving cars were supposed to be a thing back in 2017. And now, in the year of our Lord 2025, it seems like we're getting both! I also wouldn't underestimate the cultural influence of a few key people. PewDiePie sharing his journey into Arch and Hyprland with his 110 million followers is important. ThePrimeagen moving to Arch and Hyprland is important. Typecraft teaching beginners how to build an Arch and Hyprland setup from scratch is important (and who I just spoke to about Omarchy). Gabe Newell's Steam Deck being built on Arch and pushing Proton to over 20,000 compatible Linux games is important. You'll notice a trend here, which is that Arch Linux, a notoriously "difficult" distribution, is at the center of much of this new engagement. Despite the fact that it's been around since 2003! There's nothing new about Arch, but there's something new about the circles of people it's engaging. I've put Arch at the center of Omarchy too. Originally just because that was what Hyprland recommended. Then, after living with the wonders of 90,000+ packages on the community-driven AUR package repository, for its own sake. It's really good! But while Arch (and Hyprland) are having a moment amongst a new crowd, it's also "just" Linux at its core. And Linux really is the star of the show. The perfect, free, and open alternative that was just sitting around waiting for developers to finally have had enough of the commercial offerings from Apple and Microsoft. Now obviously there's a taste of "new vegan sees vegans everywhere" here. You start talking about Linux, and you'll hear from folks already in the community or those considering the move too. It's easy to confuse what you'd like to be true with what is actually true. And it's definitely true that Linux is still a niche operating system on the desktop. Even among developers. Apple and Microsoft sit on the lion's share of the market share. But the mind share? They've been losing that fast. The window is open for a major shift to happen. First gradually, then suddenly. It feels like morning in Linux land!

16 hours ago 2 votes
All about Svelte 5 snippets

Snippets are a useful addition to Svelte 5. I use them in my Svelte 5 projects like Edna. Snippet basics A snippet is a function that renders html based on its arguments. Here’s how to define and use a snippet: {#snippet hello(name)} <div>Hello {name}!</div> {/snippet} {@render hello("Andrew")} {@render hello("Amy")} You can re-use snippets by exporting them: <script module> export { hello }; </script> {@snippet hello(name)}<div>Hello {name}!</div>{/snippet} Snippets use cases Snippets for less nesting Deeply nested html is hard to read. You can use snippets to extract some parts to make the structure clearer. For example, you can transform: <div> <div class="flex justify-end mt-2"> <button onclick={onclose} class="mr-4 px-4 py-1 border border-black hover:bg-gray-100" >Cancel</button > <button onclick={() => emitRename()} disabled={!canRename} class="px-4 py-1 border border-black hover:bg-gray-50 disabled:text-gray-400 disabled:border-gray-400 disabled:bg-white default:bg-slate-700" >Rename</button > </div> into: {#snippet buttonCancel()} <button onclick={onclose} class="mr-4 px-4 py-1 border border-black hover:bg-gray-100" >Cancel</button > {/snippet} {#snippet buttonRename()}...{/snippet} To make this easier to read: <div> <div class="flex justify-end mt-2"> {@render buttonCancel()} {@render buttonRename()} </div> </div> snippets replace default <slot/> In Svelte 4, if you wanted place some HTML inside the component, you used <slot />. Let’s say you have Overlay.svelte component used like this: <Overlay> <MyDialog></MyDialog> </Overlay> In Svelte 4, you would use <slot /> to render children: <div class="overlay-wrapper"> <slot /> </div> <slot /> would be replaced with <MyDialog></MyDialog>. In Svelte 5 <MyDialog></MyDialog> is passed to Overlay.svelte as children property so you would change Overlay.svelte to: <script> let { children } = $props(); </script> <div class="overlay-wrapper"> {@render children()} </div> children property is created by Svelte compiler so you should avoid naming your own props children. snippets replace named slots A component can have a default slot for rendering children and additional named slots. In Svelte 5 instead of named slots you pass snippets as props. An example of Dialog.svelte: <script> let { title, children } = $props(); </script> <div class="dialog"> <div class="title"> {@render title()} </div> {@render children()} </div> And use: {#snippet title()} <div class="fancy-title">My fancy title</div> {/snippet} <Dialog title={title}> <div>Body of the dialog</div> </Dialog> passing snippets as implicit props You can pass title snippet prop implicitly: <Dialog> {#snippet title()} <div class="fancy-title">My fancy title</div> {/snippet} <div>Body of the dialog</div> </Dialog> Because {snippet title()} is a child or <Dialog>, we don’t have to pass it as explicit title={title} prop. The compiler does it for us. snippets to reduce repetition Here’s part of how I render https://tools.arslexis.io/ {#snippet row(name, url, desc)} <tr> <td class="text-left align-top" ><a class="font-semibold whitespace-nowrap" href={url}>{name}</a> </td> <td class="pl-4 align-top">{@html desc}</td> </tr> {/snippet} {@render row("unzip", "/unzip/", "unzip a file in the browser")} {@render row("wc", "/wc/", "like <tt>wc</tt>, but in the browser")} It saves me copy & paste of the same HTML and makes the structure more readable. snippets for recursive rendering Sometimes you need to render a recursive structure, like nested menus or file tree. In Svelte 4 you could use <svelte:self> but the downside of that is that you create multiple instances of the component. That means that the state is also split among multiple instances. That makes it harder to implement functionality that requires a global view of the structure, like keyboard navigation. With snippets you can render things recursively in a single instance of the component. I used it to implement nested context menus. snippets to customize rendering Let’s say you’re building a Menu component. Each menu item is a <div> with some non-trivial children. To allow the client of Menu customize how items are rendered, you could provide props for things like colors, padding etc. or you could allow ultimate flexibility by accepting an optional menuitem prop that is a snippet that renders the item. You can think of it as a headless UI i.e. you provide the necessary structure and difficult logic like keyboard navigation etc. and allow the client lots of control over how things are rendered. snippets for library of icons Before snippets every SVG Icon I used was a Svelte component. Many icons means many files. Now I have a single Icons.svelte file, like: <script module> export { IconMenu, IconSettings }; </script> {#snippet IconMenu(arg1, arg2, ...)} <svg>... icon svg</svg> {/snippet}} {#snippet IconSettings()} <svg>... icon svg</svg> {/snippet}}

yesterday 2 votes
Logical Quantifiers in Software

I realize that for all I've talked about Logic for Programmers in this newsletter, I never once explained basic logical quantifiers. They're both simple and incredibly useful, so let's do that this week! Sets and quantifiers A set is a collection of unordered, unique elements. {1, 2, 3, …} is a set, as are "every programming language", "every programming language's Wikipedia page", and "every function ever defined in any programming language's standard library". You can put whatever you want in a set, with some very specific limitations to avoid certain paradoxes.2 Once we have a set, we can ask "is something true for all elements of the set" and "is something true for at least one element of the set?" IE, is it true that every programming language has a set collection type in the core language? We would write it like this: # all of them all l in ProgrammingLanguages: HasSetType(l) # at least one some l in ProgrammingLanguages: HasSetType(l) This is the notation I use in the book because it's easy to read, type, and search for. Mathematicians historically had a few different formats; the one I grew up with was ∀x ∈ set: P(x) to mean all x in set, and ∃ to mean some. I use these when writing for just myself, but find them confusing to programmers when communicating. "All" and "some" are respectively referred to as "universal" and "existential" quantifiers. Some cool properties We can simplify expressions with quantifiers, in the same way that we can simplify !(x && y) to !x || !y. First of all, quantifiers are commutative with themselves. some x: some y: P(x,y) is the same as some y: some x: P(x, y). For this reason we can write some x, y: P(x,y) as shorthand. We can even do this when quantifying over different sets, writing some x, x' in X, y in Y instead of some x, x' in X: some y in Y. We can not do this with "alternating quantifiers": all p in Person: some m in Person: Mother(m, p) says that every person has a mother. some m in Person: all p in Person: Mother(m, p) says that someone is every person's mother. Second, existentials distribute over || while universals distribute over &&. "There is some url which returns a 403 or 404" is the same as "there is some url which returns a 403 or some url that returns a 404", and "all PRs pass the linter and the test suites" is the same as "all PRs pass the linter and all PRs pass the test suites". Finally, some and all are duals: some x: P(x) == !(all x: !P(x)), and vice-versa. Intuitively: if some file is malicious, it's not true that all files are benign. All these rules together mean we can manipulate quantifiers almost as easily as we can manipulate regular booleans, putting them in whatever form is easiest to use in programming. Speaking of which, how do we use this in in programming? How we use this in programming First of all, people clearly have a need for directly using quantifiers in code. If we have something of the form: for x in list: if P(x): return true return false That's just some x in list: P(x). And this is a prevalent pattern, as you can see by using GitHub code search. It finds over 500k examples of this pattern in Python alone! That can be simplified via using the language's built-in quantifiers: the Python would be any(P(x) for x in list). (Note this is not quantifying over sets but iterables. But the idea translates cleanly enough.) More generally, quantifiers are a key way we express higher-level properties of software. What does it mean for a list to be sorted in ascending order? That all i, j in 0..<len(l): if i < j then l[i] <= l[j]. When should a ratchet test fail? When some f in functions - exceptions: Uses(f, bad_function). Should the image classifier work upside down? all i in images: classify(i) == classify(rotate(i, 180)). These are the properties we verify with tests and types and MISU and whatnot;1 it helps to be able to make them explicit! One cool use case that'll be in the book's next version: database invariants are universal statements over the set of all records, like all a in accounts: a.balance > 0. That's enforceable with a CHECK constraint. But what about something like all i, i' in intervals: NoOverlap(i, i')? That isn't covered by CHECK, since it spans two rows. Quantifier duality to the rescue! The invariant is equivalent to !(some i, i' in intervals: Overlap(i, i')), so is preserved if the query SELECT COUNT(*) FROM intervals CROSS JOIN intervals … returns 0 rows. This means we can test it via a database trigger.3 There are a lot more use cases for quantifiers, but this is enough to introduce the ideas! Next week's the one year anniversary of the book entering early access, so I'll be writing a bit about that experience and how the book changed. It's crazy how crude v0.1 was compared to the current version. MISU ("make illegal states unrepresentable") means using data representations that rule out invalid values. For example, if you have a location -> Optional(item) lookup and want to make sure that each item is in exactly one location, consider instead changing the map to item -> location. This is a means of implementing the property all i in item, l, l' in location: if ItemIn(i, l) && l != l' then !ItemIn(i, l'). ↩ Specifically, a set can't be an element of itself, which rules out constructing things like "the set of all sets" or "the set of sets that don't contain themselves". ↩ Though note that when you're inserting or updating an interval, you already have that row's fields in the trigger's NEW keyword. So you can just query !(some i in intervals: Overlap(new, i')), which is more efficient. ↩

2 days ago 5 votes
The missing part of Espressif’s reset circuit

In the previous article, we peeked at the reset circuit of ESP-Prog with an oscilloscope, and reproduced it with basic components. We observed that it did not behave quite as expected. In this article, we’ll look into the missing pieces. An incomplete circuit For a hint, we’ll first look a bit more closely at the … Continue reading The missing part of Espressif’s reset circuit → The post The missing part of Espressif’s reset circuit appeared first on Quentin Santos.

2 days ago 3 votes