title: Functional Programming: Practice and Theory
author: Bruce J. Maclennan
description: This book is more than an introduction to programming in functional languages; it introduces functional programming as a new programming paradigm. Its focus is on functional programming methodology--what it is, and how it can be used to good effect. In particular, the book shows how this methodology can be used effectively in deriving, analyzing, and proving the correctness of programs. In as much as this book emphasizes general methodology over any particular language, the author has chosen standard mathematical notation for his examples.
zlib_text: © Anto Aravinth 2017
  
  Anto AravinthBeginning Functional JavaScript10.1007/978-1-4842-2656-8_1
  
  # 1\. Functional Programming in Simple Terms
  
  Anto Aravinth1
  
  (1)
  
  Chennai, Tamil Nadu, India
  
  Electronic supplementary material
  
  The online version of this chapter
  (doi:[10.​1007/​978-1-4842-2656-8_​1](http://dx.doi.org/10.1007/978-1-4842-2656-8_1))
  contains supplementary material, which is available to authorized users.
  
  
  >
  
  
  The first rule of functions is that they should be small. The second rule of
  functions is that they should be smaller than that.
  
  
  —ROBERT C. MARTIN
  
  
  Welcome to the functional programming
  
  
  world. The world, which has only functions, living happily without any outside
  world dependencies, without states, without mutations – forever. Functional
  programming is a buzz in recent days. You might have heard about this term
  within your team, in your local group meeting, and have thought about this. If
  you’re already aware of what that means, this is great! But for those who
  d