In mathematics a function is a mapping having the property that each input is related to exactly one output. This brings with it certain properties you can rely on. In particular functions themselves are also values that can be passed around as parameters or returned by other functions, hence higher order functions.

It's regrettable that we overloaded the word "function", given we could have used procedures or subroutines to denote, you know, jumps in code that trigger effects and push/pop the call stack.

And as proof, applying filter/map and other similar operations with side-effecting procedures is a really, really bad idea, because such operators are usually implemented with lazy behavior (in order for "fusion" to happen) and laziness doesn't blend well with side effects, with the result becoming non-deterministic. E.g. at least people that worked with Map-Reduce frameworks should know what I'm talking about.

Or in other words, there is no such thing as "function-oriented", there's just local application of FP where it seems to be making sense, but with all the caveats that entails.