Functional programming

A model of computation of some interest, functional programming is a style of programming that treats computation as the evaluation of mathematical functions and avoids changing state and mutable data. In functional programming, functions are first-class citizens, meaning they can be passed as arguments to other functions, returned as values from other functions, and assigned to variables. Many useful programming languages have a functional core and a more imperative shell, notably most differentiable languages, and PPLs.