

Functional languages are inherently built on non-functional ones, for the same reason that object oriented languages are built on non object oriented ones, because cpus are fundamentally not object oriented or functional.
They are computational machines with specific instructions around moving values in memory and performing certain operations on them.
Assembly / machine code is always, at a fundamental level, imperative programming, and all higher ordered languages have to translate to these imperative instruction sets / languages.
However, there is an OS that tries to be functional as much as possible though, and that’s a Linux distribution called NixOS, based on the functional language Nix.







Most major languages these days are multi-paradigm languages that can do procedural, functional, or object oriented coding.
C#, Kotlin, JavaScript, TypeScript, Go, Python, Swift, etc all fall into this bucket.
Java has made a lot of efforts to support functional programming, but it’s still not first class.
I would argue that these languages adopting functional coding as a first class citizen has made dedicated functional languages somewhat more obsolete, but they also paved the way and set the standards for the general languages that came after.
On the web side of things, the most popular JavaScript / TypeScript frameworks these days are often fundamentally functional though, from React on the front-end to Express on the back end.