Question

What is functional programming? (no copy/paste stuff)

Answer 1

Yeah, what is it?

Some say functional programming is the one true programming paradigm, yet why isn't it mainstream?

Answer 2

Functional programming is different than imperative programming in that algorithms are expressed as applying functions to data and expressing loops using recursion instead of maintaining and modifying a global state.

Answer 3

Unlike imperative programming, in functional programming functions don't have "side effects". When a function is called it does not read and write to some global state, and so when you call a function more than once with the same input you should expect the same output.

Answer 4

Yes