First, the paradigm of functional programming, just-just talking about how to write programs. The purpose of this paradigm is to formalize programs as mathematical functions.
Of course, these are some big goals, someone thinks that is the only true way of programming, someone worships the paradigm as God. But these people, excuse me for such a rude statement — fools. The truth is "between". In other words, functional programming allows to make the code more compact, beautiful, fast, but using only this paradigm, ignoring the rest — only harm.
It is important to understand what is required of the language. As I see it, the only requirement is high speed with small resources will not grow(am I right?).
If it's so critical(the 100 and 1 time, rate task!), the choice is not great: C, C++.
If you want to partake of the functional paradigm, you can try Haskell, CL(Common Lisp). But I repeat, if the problem is the word "function", it does not mean that you need to use "functional programming".