Run, if you hear FP is declarative programming

Well, that's a good point. I always saw declarative programming as something where one writes what to get out of program and does not write how to get it.

Functional programming still includes the way of how to get the result, it's just about composing dynamically created functions, tail recursion and immutability. I constantly find it hard to accept that FP is of similar class as logic programming, while FP is to me closer to imperative programming than Prolog or SQL.

(I like functional programming very much; I just don't get it why it should be called "declarative".)