Clojure for Rubyists

Clojure for Rubyists For Montreal.rb on September 21 st 2010 By Jeff Heon

Clojure in a nutshell
Functional
Concurrency
JVM
Lisp

Similarities
Interactive development
Ruby Clojure irb REPL (read eval loop print) java -cp clojure.jar clojure.main

Similarities
Ruby symbols are Clojure keywords.
Ruby Clojure :symbol :keyword

Similarities
In a conditional, nil and false evalute to false and everything else to true.
Ruby Clojure if 0 then true end => true if nil then true else false end => false (if 0 true) => true (if nil true false) => false

Similarities
Last expression in a method is the return value.
Ruby Clojure def convert_farenheit_to_celcius(f) (f - 32) * 5.0 / 9 end (defn convert-farenheit-to-celcius [f] (* (- f 32) (/ 5.0 0)))

Basic types Ruby Clojure letter_digit = /^[a-zA-Z][0-9]$/ (def letter-digit #"^[a-zA-Z][0-9]$") [0, 'Ruby', 42] my_array[0] [0 "Ruby" 42] (my-vector 0) { :r => 'Ruby', :c => 'Clojure' } #Accessing my_hash[:r] { :r "Ruby" :c "Clojure" } ;Accessing (my-hash :c)

Functional Ruby Clojure def odd?(n) (n % 2) == 1 end #Sum of odd numbers from 0 to 99 (0..99). select { |n| odd? n }. inject(0) { |acc, n| acc + n } => 2500 (defn odd? [n] (= 1 (mod n 2))) ;Sum of odd numbers from 0 to 99 (reduce + (filter odd? (range 100))) => 2500

Functional, but lazy Ruby Clojure def odd_trace?(n) puts n (n % 2) == 1 end #Sum of odd numbers from 0 to 9 (0..99). select { |n| puts n;(n % 2) == 1 }. first(10). inject(0) { |acc, n| acc + n } => prints 0 to 99, returns 100 (defn odd-trace? [n] (print n) (= 1 (mod n 2))) ;Sum of odd numbers from 0 to 9 (reduce + (take 10 (filter odd-trace? (range 100)))) => prints 0 to 31, returns 100

Immutable data structure Data structure are always immutable. Adding or removing an element to an array, vector, hash or set will always return a new collection. But, they are efficient because they are persistant (in the sense that they share structure.)

Concurrency Software transactional memory Or having multiple threads access the same reference using transactions instead of locks. STMs are not all the same (like GC) Readers are never blocked. Works hand in hand with persistant data structure.

Where did my books go? (def book1 { :author "David Flanagan" :title "The Ruby Programming language" }) (def book2 { :author "Gregory Brown" :title "Ruby Best Practices"}) (def home-books (ref #{book1 book2})) (def lent-books (ref #{})) (alter home-books disj book1) => No transaction running (dosync (alter home-books disj book1) (alter lent-books conj book1)) @home-books => #{{:author "Gregory Brown", :title "Ruby Best Practices"}} @lent-books => #{{:author "David Flanagan", :title "The Ruby Programming language"}}

Further exploration If nothing else: Are we there yet? Main site: Clojure.org News & getting started: Disclojure Books ( a comparison )
Programming Clojure
Clojure in Action
The Joy of Clojure
Practical Clojure
And one upcoming from O'Reilly

Clojure for Rubyists

by jfheon on Sep 22, 2010

Accessibility

Categories

Tags

Upload Details

Usage Rights

1 Embed 1

Statistics

Clojure for Rubyists — Presentation Transcript