Any takers?
IIRC, I have seen once an experimental language which worked exactly like in your proposal, but it was long ago and I do not remember which was it.
One LISP system that I have used long ago had a different approach. In it, one closing square bracket could be used to close all non-closed parentheses preceding it.
That was Interlisp, originally making handling of punch cards easier. Nowadays it's not necessary, since the 70s/80s text editors on terminals support handling nested expressions.
let hello = dbg!{ dbg![ dbg!("world") ] };
So it feels like this could be a reasonable plugin?
(car (first a))
(cond ((> a 10) 1)
((> b 20) 2)
((> c 30) 3))
> If different kinds of brackets had been used for every distinct purpose, then there would have been no need to count parentheses or be dependent on enforcing invariable indentation rules.
No Lisp developer counts parentheses. Indentation rules are used in many programming languages. Lisp applies these rules using tools, like many programming environments do.
If different kinds of brackets had been used for every distinct purpose, then there would have been no need to count parentheses or be dependent on enforcing invariable indentation rules.
ALGOL 68 is another example of programming language with fully parenthesized non-ambiguous syntax, but it uses many kinds of different bracket pairs, which makes it much easier to read. While some of its bracket pairs, like if/fi, do/od, case/esac, have been rightfully mocked, they achieve well their purpose.
In a programming language there are many different purposes for which bracket pairs are needed, e.g. for delimiting sub-expressions in order to change the default order of evaluation, for delimiting function argument lists, for delimiting array index lists, for delimiting blocks, for delimiting function bodies, for delimiting record/structure component definitions, for delimiting the components of various program structures, like conditional expressions and loops, and so on.
For an automatic parser, the use of different kinds of brackets can only make its task easier, never harder, because in the worst case its lexical analysis could replace all kinds of brackets with a single kind, while for a human reader different kinds of brackets are always helpful.
Using many kinds of bracket pairs is not necessarily as verbose as in Algol 68, because Unicode offers enough bracket pairs to choose for all purposes.
In LISP all parentheses look the same, but a LISP programmer who does not recognize that the things delimited in those parentheses are of different natures, e.g. "(CAR ..." vs. "(COND ..." vs. "(QUOTE ..." and so on, cannot write high quality LISP programs.
Many years ago, I have written many rather big Scheme or LISP programs, because they have many advantages beyond the uniform parentheses. If I would use again a language of the LISP family, I would use a text preprocessor to pass the source to the compiler, which would allow me to use various kinds of bracket pairs, for instance Unicode mathematical angle brackets for COND, Unicode bag delimiters for loops, curly brackets for blocks (curly bracket is the Unicode term for braces), and so on.