The document provides an overview of functional programming using Clojure, emphasizing its mathematical foundations and lambda calculus. It discusses key concepts such as first-class functions, immutability, and metaprogramming, while illustrating Clojure's syntax and data structures. Additionally, it highlights the advantages of Clojure, including its ability to facilitate concurrency and its performance compared to other programming languages.

1. Demystifying (λ)Functional Programming with
Clojure
-Rohit Vaidya

2. Agenda
● Functional Programming
● Some Functional Jargon
● Understand Clojure
● Clojure Syntax
● Lein - Build tools for Clojure
● Meta Programming

3. Functional Programming
● Functional Programming takes a
mathematical view of the world
● Nothing but elaboration of Lambda
Calculus

4. λ- Calculus
● λ-Calculus is universal model of
Computation
● Can be used to simulate a taped turing
machine
● λ-Calculus treats functions anonymously
● Computable functions are fundamental to
math and CS.
● λ-Calculus provides semantics for
computation

5. λ- Calculus
squaresum( x , y)→ x
2
+y
2
(x , y) → x
2
+ y
2
(( x , y)→ x
2
+y
2
)(4,3)
→4
2
+3
2
→25
(x →( y → x
2
+y
2
)(5))(2)
( y →5
2
+y
2
)(2)
5
2
+2
2
29

6. Jargon
● Homoiconic Language - Program
structure is similar to its syntax
● Metaprogramming - Metaprogramming is
the art of writing of computer programs with
the ability to treat programs as their data
● Referential Transparency (Pure) -
Always returns the same result for a given
argument

7. Functional Programming-Clojure
● First class functions
● Immutable Data Structures
● Recursive looping
● Facilitates concurrency

8. Why Clojure?
● A Lisp – dynamic language
● Functional Programming
● Symbiotic with an established Platform
● Designed for Concurrency
● Embraces the JVM (Native to the JVM)
● Clojure is concise – Code as Data
– (+ 3 2) This is a function call
– '(+ 3 2) This is data

9. Why Clojure?
● You can tranlate data into function call at
runtime
● Performs better than JavaScript, Ruby and
Python
● Macros- Extending the Language
– e.g: HTML templating is bloated
– In java you mix HTML with Java or Java
with HTML
– What if your language knows generating
HTML?

10. Why Clojure?
– [:a {:href "http://github.com"} "GitHub"]
– This converts to
– <a href="http://github.com">GitHub</a>
– The above can be done using Hiccup
● Has a REPL
● Define functions on the fly

11. Clojure Syntax
● ()[]{} Everything within () gets evaluated
● Almost no syntax rules
● Lisp Syntax (data = code).Code as Data!!!
● Lets write a simple function
– Anonymous Function
– Named function

12. Atomic Data Types
● Nil means nothing. Same as Java null
● Booleans true false
● Doubles 1.234 BigDecimals 10.123M
● Ratios 22/7
● Strings “fred” Characters a b c
● Regex #”a*x”

13. Atomic Data
● Use clojure.core/class function to identify
type of data

14. Clojure Functions
● Create a Clojure Function
1.Bind Name add to the function
2.Anonymous function with arguments x y
1.fn creates a anonymous function
3.Function description
4.Function body
1
2
31
4

15. Clojure Function
● Define function with macro form defn
1
2
3
1. Create a function add with x, y
arguments
2. Function description
3. Function Body

16. Clojure Function Pure vs Impure
● Referential Transparency
1. Is pure. For certain x,y it will always return
same result
2. Is impure. Getting a hike is dependent on
side effect and not always deterministic
1 2

17. Special Forms
● Primitives build in clojure to perform core
operations
● If do let fn loop recur etc are special forms
● (if true 1 2)
– Returns 1
● (let [x 3] println x)
– Prints 3
– Scope restricted to let statment

18. Lists, Vectors, Sets and Maps
● Vectors
– Similar to Array
– 0 based collection
– Syntax
● [1 2 3]
● (def abc [1 2 3])
● (get abc 0)

19. Lists, Vectors, Sets and Maps
● Lists
– Similar to Vectors
– Cannot use get against lists
– Syntax
● '(1 2 3)
● (nth '(1 2 3) 0)
● Lists to used if you want to add elements to
the beginning
– (conj '(1 2 3) 4) returns 4 1 2 3

20. Lists, Vectors, Sets and Maps
● Maps
– Similars to dictionaries or hashes
– Two types in Clojure
● HashMaps
● SortedMaps
– Syntax:
● {:firstName “Rohit” :lastName “Vaidya”}
● (def hm {:a 1 :b 2})
● (get hm :a) returns 1

21. Lists, Vectors, Sets and Maps
● HashSet
– Sets are collection on unique values
– Syntax
● (hash-set 1 2 3 3 2 1)
– Create a hash set
● (contains? (hash-set 1 2 2 1 1) 1)
– Check presense of a element
– Returns true

22. Lists, Vectors, Sets and Maps
● HashSet
– Sets are collection on unique values
– Syntax
● (hash-set 1 2 3 3 2 1)
– Create Hash Set
● (contains? (hash-set 1 2 2 1 1) 1)
– Check presense of element
– Returns true

23. Programming to Abstractions
● Sequence Abstraction, abstracts
– List,
– Vector
– Set and Map
● Clojure defines map and reduce in terms of
sequence abstractions and not any specific
data structure
● y1 = f(x1), y2 = f(x2), . . . yn = f(x n).

24. Programming to Abstractions
● Visualizing mapping on a sequence abstraction

25. Programming to Abstractions
1. Define a increment function
2. Function description
3. Argument
4. Function Body
5. Map applied to a sequence(Vector). Map is a higher order function
1
2
3
4
5

26. Loops using Recursion
1. First function overload
with zero arugment with
arity 0
2. Second function overload
with 1 argument i.e arity 1
3. Recursive call to by
passing incremented
value of number
1
2
3

27. Loops with Recursion
1
2
• Clojure equivalent of 1 in 2

28. Metaprogramming – Alchemy
● Reader: Is a clojure Parser
– Converts text into clojure data structure
● Read String converts to list

29. Metaprogramming - Alchemy
1. Read a string and convert to list (data)
2. Read a String and evaluate it. Clojure expected operator.
3. Constructed prefix (reverse polish) with infix expression
4. Evaluated the constrcuted prefix expression
1
2
3
4

30. Metaprogramming - Alchemy
● Defmacro defines a
macro
● Lesser verbose,
metaprogramming
1. Define a macro
2. Argument for macro
3. Prefix to infix
4. Call to a macro
1
2
3
4

31. High Order Functions
● When a language takes a fn as arugment
or returns fn as result
● A higher order function is
– A function that takes function arguments
– A function that retuns a function
● Some well known higher order functions
– Map Reduce Remove
Filter Iterate

32. Lein – the build tool
● Lein commands
– lein new app clojure-noob
– lein run
– lein test
● Lein web app
– lein new luminus my-app
– cd my-app
– lein run

33. References
● https://clojurebridge.github.io/community-docs/
● http://www.slideshare.net/smartrevolution/how-a-
● http://www.braveclojure.com/
● http://xahlee.info/clojure/clojure_index.html
● https://www.gnu.org/software/emacs/
● https://mitpress.mit.edu/sicp/
● Clojure by Rich Hickey
● 4Clojure

34. SICP