[racingmars]

> Value Database

> Smalltalk and another esoteric programming environment I used for a while called Frontier had an idea of a persistent data store environment. Basically, you could set global.x = 1, shut your program down, and start it up again, and it would still be there.

Frontier! I played with that way back when on the Mac. Fun times.

But as for programming language with integrated database... MUMPS! Basically a whole language and environment (and, in the beginning, operating system) built around a built-in global database. Any variable name prefixed with ^ is global and persistent, with a sparse multi-dimensional array structure to be able to organize and access the variables (e.g. ^PEOPLE(45,"firstname") could be "Matthew" for the first name of person ID 45). Lives on today in a commercial implementation from Intersystems, and a couple Free Software implementations (Reference Standard M, GT.M, and the GT.M fork YottaDB). The seamless global storage is really nice, but the language itself is truly awful.

[SeenNotHeard]

TADS, an OOP language + VM for interactive fiction, has this "value database" model. Once loaded into memory, the compiled image can be updated with values stored in a separate save file. The compiled image itself could store updated values as well.

In fact, it does this during a "preinit" stage that runs immediately after compilation. Once all preinit code finishes executing, the compiled image is overwritten with the updated state. The language includes a "transient" keyword to permit creating objects that should not be stored.

This same mechanism permits in-memory snapshots, which are used for the game's UNDO feature. No need to rewind or memento-ize operations, just return to a previous state.

It's not a general-purpose mechanism. After all, the language is for building games with multiple player-chosen save files, and to permit restarting the game from a known Turn 0 state.

[kweingar]

The MUMPS database is wild. When I was working in MUMPS, it was so easy and fun to whip up an internal tool to share with my coworkers. You don't have to give any special thought at all to persistence, so you're able to stay in the flow of thinking about your business logic.

But as you said, the language itself is almost unbearable to use.

[danielhlockard]

I had a professor who is responsible for a lot of the more "modern" MUMPS stuff (lets be real, MUMPS is OLD!). Guy was pretty unbearable too.

[jonathaneunice]

Image persistence was one of the cool ideas of Smalltalk. And in practice, one of the biggest drawbacks. Cruft and old values accumulated steadily, with very little way to find and eliminate them. Transient execution has some cons. But on the pro side, every run starts from a "clean slate."

[igouy]

And in practice, both.

Save image... for short-term convenience; build clean every week from archived text files.

----

1984 "Smalltalk-80 The Interactive Programming Environment" page 500

"At the outset of a project involving two or more programmers: Do assign a member of the team to be the version manager. … The responsibilities of the version manager consist of collecting and cataloging code files submitted by all members of the team, periodically building a new system image incorporating all submitted code files, and releasing the image for use by the team. The version manager stores the current release and all code files for that release in a central place, allowing team members read access, and disallowing write access for anyone except the version manager."

https://rmod-files.lille.inria.fr/FreeBooks/TheInteractivePr...

[jimbokun]

So the "version manager" is a human git repository!

[igouy]

40 years ago, yes!

In the same way that "network" had recently been sneaker-net.

[brabel]

> with very little way to find and eliminate them.

The best Smalltalk these days is GlamorousToolkit: https://gtoolkit.com/

It has a sort of git in it, so you can easily "rollback" your image to previous states. So going back and forth in history is trivial.

[galaxyLogic]

> you can easily "rollback" your image to previous states.

Sounds very interesting. Does it support multi-developer merging and/or rebasing of changes?

[brabel]

I believe it's just a git repo behind the scenes. Not sure if the UI exposes those things as I never used that in multi-developer scenarios! Give it a go and see.

[whartung]

This may fall in the "you think you do, but you don't category", but I've always wanted a Smalltalk (or similar, not that picky) with a persistent virtual memory.

That is, the VM is mapped to a backing file, changes persisted automatically, no "saving", limited by drive space (which, nowadays, is a lot). But nowadays we also have vast memory space to act as a page cache and working memory.

My contrived fantasy use case was having a simple array name "mail", which an array containing all of my email messages (in email object, of course). Naturally as you get more mail, the array gets longer. Also, as you delete mail, then the array shifts. It's no different, roughly, than the classic mbox format, save it's not just text, its objects.

You can see if you delete a email, from a large (several GBs), there would be a lot of churn. That implies maybe it's not a great idea to use that data structure, but that's not the point. You CAN use that data structure if you like (just like you can use mbox if you like).

Were it to be indexed, that would be done with parallel data structures (trees or hashes or whatever).

But this is all done automagically. Just tweaks to pages in working memory backed by the disk using the virtual memory manager. Lots and lot of potential swapping. C'est la vie, no different from anything else. This what happens when you map 4TB into a 16GB work space.

The problem with such a system, is how fragile is potentially is. Corrupt something and it happily persists that corruption, wrecking the system. You can't reboot to fix it.

Smalltalk suffers from that today. Corrupt the image (oops, did I delete the Object become: method again?), and its gone for good. This is mitigated by having backup images, and the changelist to try to bring you back to the brink but no further.

I'm guessing a way to do that in this system is to use a copy on write facility. Essentially, snapshot the persistent store on each boot (or whatever), and present a list of previous snapshot at start up.

Given the structure of a ST VM you'd like to think this is not that dreadful to work up. I'd like to think a paper napkin implementation PoC would be possible, just to see what it's like. One of those things were the performance isn't really that great, but the modern systems are so fast, we don't really notice it in human terms.

But I do think it would be interesting.

[igouy]

Smalltalk suffers from mis-information —

> oops, did I delete the Object become: method again?), and its gone for good.

And then you admit actually it's not gone for good because if you created the method that will be recorded in the changes.log file and if it was a provided method that will still be in the provided sources file.

https://cuis-smalltalk.github.io/TheCuisBook/The-Change-Log....

[cess11]

Have you looked at Pharo? Their git integration makes it relatively easy to export and backup parts of your main image, and to pull the things back into a fresher one once you mess up.