Clojure is a Lisp dialect created by Rich Hickey in 2008 that runs on the Java Virtual Machine. It is a dynamic, functional programming language with immutable persistent data structures and supports proper equality semantics. Clojure code is made up of data structures and uses homoiconicity, where code is represented as standard data structures. It has many standard data types like integers, doubles, ratios, strings, symbols and keywords, as well as collection data structures like lists, vectors, and maps.

1. Introduction to Clojure
By Abhishek Mahawar
BM Tech Talk

2. Not so old History
● Created by Rich Hickey
● First version in 2008
● Origin of name - Wanted to involve c(c#), l
(lisp) and j(java).

3. Clojure is a ….
● LISP dialect targeting the JVM
● Dynamic programming language
● Functional programming language
● Compiled language

4. Clojure is a LISP
● S-expressions (Polish notation)
(+ 2 4)
● Homoiconicity
code is data, data is code
● Reader
Operator/function names Arguments

5. Atomic Data Types
● Arbitrary precision integers 123
● Doubles 1.23 , BigDecimals 1.23M
● Ratios 22/7
● Strings “bm” , Characters b
● Symbols bm , Keywords :bm
● Booleans true false, Null - nil

6. Data Structures
● Lists (1 2 3)
● Vectors [1 2 3]
● Maps {:a 1 :b 2}
maps are functions of their keys
● Sets #{1 2}

7. Data Structures (contd.)
● Clojure data structures are
○ persistent
■ previous version remains intact when modified
○ immutable
○ support proper equality semantics in their
implementation of equals

8. Syntax
● We’ve just seen it !!
● No text based syntax
● Data structures are the code
Homoiconicity
● Actually, syntax is in the interpretation of
data structures

9. Clojure Evaluation
Clojure
code
Reader
characters
evaluator/
compiler
data structures
JVM
Output
bytecode

10. Expressions
● Everything is an expression
● All data literals represent themselves,
except
○ symbols - looks for binding to value
○ lists - an operation form
■ (operation arguments)
■ operation can be special ops, macros or
functions

11. Special ops/forms
● Can have non-normal evaluation of
arguments
○ (def name value-expr)
○ (if test-expr then-expr else-expr)
■ conditional, evaluates only one of then/else
● fn, let, loop, recur, do, new, ., throw, try,
set!, quote, var, monitor-enter, monitor-
exit

12. Functions
● First class values
○ (def five 5)
○ (def add-1 (fn[x] (+ x 1)))
○ (add-1 five) = 6
● Higher order functions (HOF)
● fn special op is used to create functions

13. Lots of other stuff
● Software Transactional Memory
● Macros
● Lazy Sequences
● Metadatas

14. References
● http://clojure.org/
● http://www.youtube.com/clojuretv
● Clojure Programming by Chas Emerick,
Brian Carper and Christophe Grand