But Rust is still a controlled language in that there's a language committee updating it. It's just that the committee actually listens to its community.
A true bottoms-up-controlled programming language would have to allow users to redefine keywords and grammar, then allow users to drift the language over time. Eventually you'll have multiple subgroups (accents) and one person's compiler might choke on the line `if x ain't 3`
Forth probably even more, since most things that are statements in other languages can be defined inside Forth, and you can end up easily building mutually incomprehensible DSLs even if they're technically runnable by the same interpreter.
Forth was the other example that came to mind. And possibly Haskell and Scala. But Lisp is the one that's well known with language extensibility as an advertised feature.
_Users_ can't redefine keywords and grammar in SQL, can they? All you can do is create data structures, and write functions and procedures.
Yes, you can write code that creates functions and procedures; it might even be possible to write code that modifies itself, but that still would be essentially different from what one can do in Lisp and Forth.
A true bottoms-up-controlled programming language would have to allow users to redefine keywords and grammar, then allow users to drift the language over time. Eventually you'll have multiple subgroups (accents) and one person's compiler might choke on the line `if x ain't 3`