swi-mqtt-pack VS hackernews

Not a lot of code but a somewhat different use of Prolog than you're likely to see elsewhere. I used my fork of a MQTT library for Prolog (https://github.com/sprior/swi-mqtt-pack) to implement the central controller for my home automation system. The system responds to MQTT events and then coordinates the appropriate action by sending MQTT messages to other home services. Recent versions of SWI-Prolog also support redis and I've started using that to store device configuration and state between services. The MQTT version is actually a reimplementation of my previous version which used CORBA for inter-service communication.

I don't distribute the home automation code however it's pretty specific to my house. The MQTT library provides some building block examples.

I forked an abandoned implementation of MQTT for SWI-Prolog by olsky, my fork is at https://github.com/sprior/swi-mqtt-pack

Look in the examples directory for some basic pub/sub code.

The Prolog code that runs in my house is pretty specific to my house so I figured the best way to open source things would be as a framework more than an implementation. You can contact me via issues on the github repo and prod me into adding some more advanced examples - I've learned a lot since my last commit on the repo.

I've started using the Redis functionality recently added to SWI-Prolog, so my code now responds to MQTT messages and uses state queried from Redis to help determine what actions (implemented by sent MQTT messages) to send out. The beauty is that since I don't do anything that blocks significantly in the Prolog code it is now single threaded - even the MQTT listening. It still responds quickly enough and is MUCH easier to deal with than multi-threaded.

An example of what I'm doing is I built a bunch of ESP8266/EESP32 display devices that control neopixels/OLED/LCD displays. When one of those devices boots it sends a MQTT message announcing its location and capabilities (display type, bit depth, dimensions). Prolog receives that message and then stores that info in Redis. So that device info is all dynamic.

So then later Prolog might get a notification that something is in the driveway. All by MQTT it requests an image from the appropriate camera, then sends the image off to Sighthound and deepstack image recognition servers. The Sighthound front end sends a message back to Prolog with a description of any vehicle spotted which Prolog then matches against known vehicles. If it determines for example that a Fedex truck is in the driveway then Prolog sends notifications around the house - it queries all the display devices from Redis and then based on the capabilities of each devices creates a JSON formatted MQTT message to send to each announcing the Fedex truck. It then also sends a MQTT message to some Java code that connects with Google and sends a push message to an Android app I wrote that displays the alert on my phone and watch.

Before I switched to MQTT I was using Prolog with CORBA as the message transport and back then I also had Visual Basic and MS Agent as part of the system. One night I got bored and a little while later had 3 Peedy the Parrot characters singing Row Your Boat in a round across three different computers coordinated by Prolog. It was actually only a page worth of custom Prolog code for that.

this might help a little: https://github.com/wting/hackernews

I think it's a ratio of votes to time. I think as little as 4 votes can get something on the homepage if they come in fairly quickly.

The source code for hn is available if you want to go and look up the specifics. I'm not sure if this is the most up-to-date mirror, but the site doesn't change that often: https://github.com/wting/hackernews

Might not count as modern, but the original Reddit and HackerNews codebases:

- https://github.com/reddit-archive/reddit1.0

- https://github.com/wting/hackernews (actually news.arc, based on old hn)

There's also this https://github.com/wting/hackernews -- which is a version of the source code to the site from sometime in the past.

"Otherwise" was the operative word in my (slightly sarcastic) example. :)

Avoiding all caps words means you sometimes have to go back and change "FAA" back from "Faa".

HN's software is no longer open source, but at one time, this is how it processed titles on initial submission: https://github.com/wting/hackernews/blob/master/news.arc#L15...

And at any rate, #1 on HN is not the product of any simple rule like "most upvotes per unit time with some decay function applied." There is significant judgment in expressed in the way that stories are ranked. The sourcecode as of 2012 was enough to demonstrate this, but in my understanding yet more judgment has been applied since then.

https://github.com/wting/hackernews/blob/master/news.arc

"ad-hoc filesystem based solution" is the closest of your definitions, I think. Last time I saw/heard, HN was built in Arc, a Lisp dialect, and use(s/d) a variant of this (mirrored) code: https://github.com/wting/hackernews

Check out around this area of the code to see how simple it is. All just plain files. A database, of sorts, but not in the way you might be expecting: https://github.com/wting/hackernews/blob/master/news.arc#L16...

There is a modern maintained variant at https://github.com/arclanguage/anarki/tree/master/apps/news as well.

File syncing between machines is pretty much an easily solved problem. I don't know how they do it, but it could be something like https://syncthing.net/ or even some scripting with `rsync`. Heck, a cronned `tar | gzip | scp` might even be enough for an app whose data isn't exactly mission critical.

The old version in arc, mirrored at https://github.com/wting/hackernews/blob/5a3296417d23d1ecc90..., uses the file system as a database.

https://github.com/wting/hackernews/blob/5a3296417d23d1ecc90... shows the monotonically increasing number:

  (def new-item-id ()