Functional Programming in C#: Classic Programming Techniques for Modern Projects

WHAT IS FUNCTIONAL PROGRAMMING?

In spite of the close coupling to LISP in its early days, functional programming is generally regarded a paradigm of programming that can be applied in many languages — even those that were not originally intended to be used with that paradigm. Like the name implies, it focuses on the application of functions. Functional programmers use functions as building blocks to create new functions — that’s not to say that there are no other language elements available to them, but the function is the main construct that architecture is built from.

Referential transparency is an important idea in the realm of functional programming. A function that is referentially transparent returns values that depend only on the input parameters that are passed. This is in contrast to the basic ideas of imperative programming, where program state often influences return values of functions. Both functional and imperative programming use the term function, but the mathematical meaning of the referentially transparent function is the one used in functional programming. Such functions are also referred to as pure functions, and are described as having no side effects.

It’s often impossible to define whether a given programming language is a functional language or not. On the other hand, it is possible to find out the extent to which a language supports approaches commonly used in the functional programming paradigm — recursion, for example. Most programming languages generally ...