What is Functional Programming?

Functional languages have some restrictions that will shock traditional coders. This follows from our previous blog on Why Bother with OOP?

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So What Is It?

Some Key Principles

Why Bother?

Functional Coding in Action

Other Bits



So What Is It?Calculate

Functional Programming is a programming paradigm or toolset. As such it is programming language independent. It is radically different from other paradigms like Object Oriented (OO) and Imperative programming. It is firmly rooted in mathematics. Haskell is a popular contemporary functional language. C# 3.0, JavaScript and Java 8 are languages that allow functional, OO and imperative coding.

Functional coding has been used in industrial and commercial applications by a wide variety of organizations including FaceBook.

Here is a Wikipedia article on functional programming.


Some Key Principles

A key principle is all computation is the execution of a function. What is a function? A function maps input parameters to outputs. Here are examples that take one and two inputs.

f(x) = x + 2

g(x,y) = 2x + y + 2

 Let us call these functions.

      f(3) = 3 + 2 = 5

      g(4,5) = 2 * 4 + 5 + 2 = 15

The function cannot change the inputs. It is immutable or unchangeable. It encapsulates its data. This means there are no unpredictable side effects from a function call.

brain cell

A function is a bit like a neuron in a human brain. These neurons work independently. There are fibres that take in signals from other neurons and fibres that take signals out. By wiring together billions of neurons, highly complex tasks are accomplished.

Functional languages have some restrictions that will shock traditional coders. There are no global variables or variable reassignments. Also loops with counter variables are banned.

Functional languages mostly use recursive functions to get things done.  These functions repeatedly call themselves to implement repeated statements.

Why Bother?

Functional code provides a range of benefits.

  1. Ease of application maintenance – easy to find and fix bugs as each function is self contained.
  2. Code security – it is hard for a code hack to spread through functional code.
  3. Ease of parallel processing – it is safe to execute functions simultaneously in separate processors.
  4. Memory management – functional languages remove redundant data from memory.

Functional Coding in Action

Consider the problem of adding a series of integers. In Java we can use a familiar loop construct.


int total = 0;
for (int i = 0, i<=10, i++)
total = total + i;

In Haskell we cannot use variable reassignments or loops. But we can use a series of recursive function calls. The function sum[] calls itself to add up the integers. Here ns mean multiple n’s.

sum::[[int]] - - > int
sum[[n]] = n
sum[n:ns] = n + sum ns

 This is a call to our function with four inputs.

 sum [1,2,3,4]

It is worth mentioning that, as the problem is quite simple, both these snippets compile to similar native code. With similar performance.

Functional programming is a programming paradigm in C# that is frequently combined with object oriented programming. In C#, you will define something like:


This is C# LINQ query – but it is also functional programming. LINQ is just one .Net class library that enables you to use functional programming concepts.

To find out more take a look at these tutorials in the TalkIT C# course.

  • LINQ to Objects
  • Delegates and Events

Other Bits

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Photos www.freedigitalphotos.net/

Thanks to Computerphile for the YouTube video

David Ringsell TalkIT 2017 ©


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