In
computer science,
functional programming is a
programming paradigm—a style of building the structure and elements of computer programs—that treats
computation as the evaluation of
mathematical functions and avoids changing-
state and
mutable data. It is a
declarative programming paradigm, which means programming is done with
expressions. In functional code, the output value of a function depends only on the arguments that are input to the function, so calling a function
f twice with the same value for an argument
x will produce the same result
f(x) each time. Eliminating
side effects, i.e. changes in state that do not depend on the function inputs, can make it much easier to understand and predict the behavior of a program, which is one of the key motivations for the development of functional programming.