Question

What is functional programming?

Answer 1

Functional programming is a branch of programming that emphasizes a few different things, but the core tenet is immutability; which is to say, you cannot change a value once it has been set. When you do operations on lists of things, the result is a new list, not a modification of the original list. There is also a strong preference for using anonymous functions and higher-order functions (functions passed to functions) to achieve certain goals (some examples include filtering, mutation, etc).

Answer 2

How can you get things done when everything is immutable?

Answer 3

Why are modern languages (like C# and C++) inheriting more and more 'functional programming' features?

Answer 4

Python also has a bunch of functional programming features

Answer 5

Sometimes it's easy—think of list maps for example. These create a new list from an existing list, making changes along the way. No mutable state is needed for that.

In other cases, it requires backflips. Input-output is a good example. Pure functional languages like Haskell do some pretty crazy stuff to maintain immutability in these situations.