Clojure intro

Agenda

• Background
• What is Clojure?
• Why Clojure?
• Some code..

Clojure Vocabulary
Functional LISP STM
Programming
lambda calculus
recursion
(λ)
preﬁx notation
JVM
Lazy Sequences macros

homoiconicity REPL S-expressions

Programming Taxonomy
http://en.wikipedia.org/wiki/
Comparison_of_programming_paradigms

What is Clojure?

Clojure is a dynamic, strongly
typed, functional, high
performance implementation
of Lisp on the JVM (and CLR
and yes JavaScript)

What is Lisp?
LISP stands for LISt Processing.
Designed by John McCarthy.
Implementation of lambda
calculus.
Oldest Language - Circa 1958
Uses Lots of ( )s - Polish Preﬁx
notation
Known for AI, DSLs etc

Example LISP Code

http://kazimirmajorinc.blogspot.in/2012/03/few-examples-of-lisp-code-typography.html

What is lambda calculus?
• Formal system computation by
for expressing
in Computer Science

functions
• Consists of λ expressions
• variables v1, v2, ..., vn, ...
• the abstraction symbols λ and .
• parentheses ( )
• Examples
• λx.x — is a function taking an argument x,
and returning x Alonzo Church

• f x — is a function f applied to an argument x

Clojure History
• Project led by Rich Hickey
• 1.0 in 2007

• 1.1 in 2009

• 1.2 in 2010

• 1.3 in 2011

• 1.4 in 2012

• 1.5 released in March 2013

• Maintained on Github

• contains one jar ﬁle clojure.jar

• You can get it from Maven repo

http://java.dzone.com/articles/results-2012-state-clojure

Q: How long have you been using Clojure?

Q: What language did you use just prior to adopting Clojure ?

Q: How would you characterize your use of
Clojure today?

Q: In which domain(s) are you using Clojure?

Q: What have been the biggest wins for you in
using Clojure?

Q: Which development environment(s) do you
use to work with Clojure?

Why Clojure?
• Good at working with Data

• Rich literal types like arrays, sets, data types

• Good at expressing algorithms

• Functional

• Great for concurrency

• Immutable data structure

• Innovative approach to state - STM

Data literals
(1 2 3 "this" "is" :a :list)
[1 2 3 "this is a vector"]
{:key "value" :two 2 }
#{"I" "am" "set" }

(println "this is a function call")

fn call


fn call arguments


fn call arguments


list

syntax

(fn-name arg1 arg2 arg3 ...)

Functional Programming
A pure Function

A impure Function

A pure Function
don’t
...look outside their box
Arguments (Perform ...modify anything, anywhere
...print messages to the user
calculations, may ...write to disk

Return Value call other pure i.e. No Side Effects

functions) E.g. f(x) = x * x + 1

A impure Function

A pure Function
don’t
...look outside their box
Arguments (Perform ...modify anything, anywhere
...print messages to the user
calculations, may ...write to disk

Return Value call other pure i.e. No Side Effects

functions) E.g. f(x) = x * x + 1

A impure Function
Arguments Read External State
(perform
Return Value calculations) Write External State
(Side Effect)

Functional
Programming
• Project Euler (http://projecteuler.net)

Functional
Programming
• Problem 1: If we list all the natural numbers
below 10 that are multiples of 3 and 5, we
get 3,5,6,9. The sum of these mutiples is 23.

Functional
Programming
• Problem 1: If we list all the natural numbers
below 10 that are multiples of 3 and 5, we
get 3,5,6,9. The sum of these mutiples is 23.
Find the sum of all the multiples of 3 and 5
below 1000.

Project Euler: range

• I need a function to get a list of numbers


(range 5) => (0 1 2 3 4)


(range 5) => (0 1 2 3 4)
• So to get a range of (0-999) we can do


(range 5) => (0 1 2 3 4)
• So to get a range of (0-999) we can do
(range 1000)

Project Euler:numbers
that are divisible by
3 and 5

• zero?
• rem

Project Euler: filter

• Next something that returns a list of
selected values from a larger list
(filter even? (range 5)) => (0 2 4)
• filter function takes a predicate and a
sequence (aka collection)

Project Euler: reduce
• Finally something to add up these numbers
• reduce takes a function and a sequence.
Applies the function to the ﬁrst two
elements of the sequence, then applies the
function to the result and third item and so
on
(reduce + (range 6)) ==> 15

Project Euler:Completed
program
(defn div_by_3_or_5? [n]
(or (zero? (rem n 3))
(zero? (rem n 5))
)
)
(reduce +
(ﬁlter div_by_3_or_5?
(range 1000)
)
)

Books / Resources
http://alexott.net/en/clojure/video.html

Example of Clojure Code
10 threads manipulating one shared data structure, which consists of 100 vectors each one
containing 10 (initially sequential) unique numbers. Each thread then repeatedly selects two
random positions in two random vectors and swaps them. All changes to the vectors occur
in transactions by making use of clojure's software transactional memory system. That's
why even after 100 000 iterations of each thread no number got lost.
(defn run [nvecs nitems nthreads niters]
(let [vec-refs (vec (map (comp ref vec)
(partition nitems (range (* nvecs nitems)))))
swap #(let [v1 (rand-int nvecs)
v2 (rand-int nvecs)
i1 (rand-int nitems)
i2 (rand-int nitems)]
(dosync
(let [temp (nth @(vec-refs v1) i1)]
(alter (vec-refs v1) assoc i1 (nth @(vec-refs v2) i2))
(alter (vec-refs v2) assoc i2 temp))))
report #(do
(prn (map deref vec-refs))
(println "Distinct:"
(count (distinct (apply concat (map deref vec-refs))))))]
(report)
(dorun (apply pcalls (repeat nthreads #(dotimes [_ niters] (swap)))))
(report)))

(run 100 10 10 100000)

Clojure intro

More Related Content

What's hot (20)

Similar to Clojure intro (20)

Recently uploaded (20)

Clojure intro