This document provides an introduction to functional programming concepts and the Clojure programming language. It outlines what will be covered, including looking at programming without for-loops or mutable data, understanding functional programming basics in the context of Clojure, and why considering a functional style and Clojure may benefit projects. Key functional programming concepts like pure functions, recursion over iteration, and referential transparency are introduced. Clojure is described as a Lisp for the JVM that uses an immutable and functional style while interoperating with Java. The document gives examples of Clojure syntax including functions, lists, and map/filter/reduce operations before concluding with questions.

1. Introduction to Functional
Programming and Clojure
@sdaas

2. What to Expect …
• Look at programming in a different way
– Immutable data
– A world without for-loops
• Understand basics of functional programming
– In the context of Clojure
• A POV on why to consider a functional
programming style in your current project
• And why Clojure might be a good choice

3. What NOT to Expect …
• NOT a deep dive into all aspects of the Clojure
programming language
• NOT about installation, debugging,
performance, etc. of Clojure
• NO bashing of Java or any other language
• NO bashing of Object-Oriented Design

4. Don’t forget Java yet …
• FP is a programming paradigm or style
• Some languages lend themselves better to
functional programming
– Clojure, Haskell, Erlang
• Most languages support FP to some extent
– Java 8
– JavaScript
– Python

5. Functional Programming Concepts
• More like Mathematical Functions
– vs. Subroutines/procedures
• Support higher order functions
• Pure functions – with no side effects
• Recursion is favored over iteration
• Lazy Evaluation
• Referential Transparency
– Once defined, a “variable” never changes value

6. What is Clojure ?
• Created by Rich Hickey
• Immutable and Functional Programming style
• Lisp that runs on the JVM
• Interoperates with Java
• Power of Functional Programming meets the
Richness of Java Ecosystem

7. Clojure Syntax

8. Functions

9. Lists
• Collection of heterogeneous values
• Operations on lists never modify the original
list. They always return a copy.
• This “immutability” of data structure is a big
deal in Functional Programing.
• Two fundamental operators – first, & rest
• Every data structure and function is built up
using these two operators

10. Lists

11. Building Blocks – first & rest
• Favoring recursion over iteration
• Do you see the bomb in the nth-element ?

12. Tail recursion is your friend

13. Map, Filter, and Reduce

14. Composition
• FP encourages you to compose small/simpler
function to create complex functions

15. What does this code do ?

16. Sum of square of all odd numbers ..
• How testable and maintainable is this code ?
• Modify this for odd numbers that aren’t multiples of 7 ?
• How would this work for infinitely long data ?

17. Functional Version …

18. Find the first 20 prime numbers

19. Laziness is good ...
• Iterate : returns lazy sequence of f(x) f(f(x)) etc ..
• take : returns a lazy sequence of first n from collection
• Map and filter can work on lazy sequences
• Check out the call to java.lang.Math.sqrt

20. Hash Maps

21. Reading a CSV File …
FROM
Smith,John,45,90210
Frank,Peter,25,90110
Bond,James,38,90110
TO
{:zip 90210, :age 45, :fname "John", :lname "Smith"}
{:zip 90110, :age 25, :fname "Peter", :lname "Frank"}
{:zip 90110, :age 38, :fname "James", :lname "Bond"}

22. 12 lines of Clojure Code …

23. What the %$*&^ was that ?

24. In Summary …
• FP concepts can be used to create concise,
highly modular, and composable code
• Java 8 and JavaScript have good support for FP
concepts
• Clojure interoperates well with Java, and could
be a good way to experiment with FP without
abandoning the Java ecosystem

25. Questions ?
Please give your feedback at
http://bit.ly/introfp

26. Resources
• The SICP Book “Structure and Interpretation of
Computer Programs”
• Paul Graham’s Blogs
• Clojure Home page (clojure.org)
• Clojure for the Brave and True (braveclojure.com)
• www.slideshare.net/SoumendraDaas/present
ations
• www.github.com/sdaas/clojure-talk
• https://medium.com/@sdaas/functionally-
speaking-f4dba2a1c7ee