Earlier quoted context omitted.
I disagree, the language itself is one of the more elegant parts of the system, and enables a lot of the rest of the elegance. From a purely programming language theory, it's pretty unique. I once tried to find a language that had all the same properties, and I failed. The Factor language is probably the closest. But they are still pretty different.
The relevant programming paradigm is string/term rewriting, which is featured in other programming languages such as Pure. It seems to have few direct applications outside of symbolic computing itself, compilers and related fields such as PL theory. (Formal calculi and languages are often specified in PL theory as rewrite rules, even though the practical implementation may ultimately differ.)
It was Kernel that was most similar with the fexpr capability.
Pure is a good example too.