The idea of programming language generations were based on paradigms of programming that never really caught on. The idea, roughly, is that 3GL are those languages where you specify how something is to be done, 4GL is where you specify what is to be done instead, and 5GL is you specify the problem and the computer does everything for you.
This breaks down with the fact that it's really difficult, outside of really constrained spaces, to turn a "what" specification into a high-performance implementation, so any practical language needs to let you give some degree of control in the "how", and as a result, any modern language is somewhere uncomfortably between the 3GL and 4GL in the paradigm, not fitting entirely well in either category.
The modern analogue of 4GLs would be the promise of LLMs letting you write prompts so you don't have to learn a programming language; the promise of the original 4GLs like Pearl (not to be confused with perl) and Objectstar was to let you have non-programmers writing business logic without being COBOL or FORTRAN programmers.
Ironically, the whole reason COBOL has its weird-ass syntax was to let you have non-programmers writing business logic without being assembly or C programmers. We can see how well that worked.
I think about that every time I hear someone saying LLMs will make programmers unemployable. There’s no doubt that the work will change but I think a lot of the premise is based on a fundamental misunderstanding of the problem: business systems are just more complex than people like to think so you’re basically repeating https://xkcd.com/793/ where people higher on the org chart think the problem is just cranking out syntax because they “know” how it should work.
I think we’ve had at least 4 generations of that idea that reducing coding time will be a game-changer: the COBOL/SQL era of English-like languages promising that business people could write or at least read the code directly, 4GLs in the 80s and 90s offering an updated take on that idea, the massive push for outsourcing in the 90s and 2000s cutting the hourly cost down, and now LLMs in the form being pushed by Gartner/McKinsey/etc. In each case there have been some real wins but far less than proponents hoped because the hard problem was deciding what it really needed to do, not hammering out syntax.
There’s also a kind of Jevons paradox at work because even now we still have way more demand than capacity, so any productivity wins are cancelled out. At some point that should plateau but I’m not betting on it being soon.
4GL was really more a marketing slogan than a true generation. The idea was something like "with third generation tools, you have to drive the car, making every turn yourself, with 4th Gen., you say "Go to the Ritz!".
It wasn't true, although they did make some operations easier in tangible ways.
Rust is a wholly different kind of thing -- not easier than, say, Java, but lots more control with better guarantees. It's more a systems programming language. 4GLs were all application-focused.
