Quick introduction to Clojure @ Programmers in Padua

1. (intro "Clojure")
Matteo Barbieri
barbieri.matteo@gmail.com
@matteobarbieri

2. ?

3. Clojure is a dinamically-typed functional
language (LISP dialect) running as an hosted
language on the JVM (and JS) with a focus on
interactivity, immutability, no side effects,
laziness and concurrency

4. ©2007 Rich Hickey

5. LISP dialect

7. lang=knparens

9. var people = [{name: "Matteo", age: 33},
{name: "Paolo", age: 25},
{name: "Luca", age: 55}];
people.filter(function isYoung(p) {
return p.age < 34;
}).map(function(p) {
return p.age;
}).reduce(function(a,b) {
return a + b;
},0);

10. 13

12. (def people [{:name "Matteo" :age 33}
{:name "Paolo" :age 25}
{:name "Luca" :age 55}])
(defn young? [p] (< (:age p) 34))
(apply + (map :age (filter young? people)))

13. 12

14. =12
=13

17. SIMPLE

18. SIMPLE MADE EASY
https://www.infoq.com/presentations/Simple-Made-Easy

19. SIMPLE ≠ EASY

20. DIFFICULT → EASY

23. SIMPLE | COMPLEX

26. SIMPLE

29. if (x + y > 0) x else y

30. AST = Abstract Syntax Tree

31. if
cond elsethen

32. if
(x + y > 0) yx

33. if
> yx
x + y 0

34. if
> yx
+ 0
x y

35. if
> yx
+ 0
x y
if (x + y > 0) x else y

36. if
> yx
+ 0
x y

38. UNLESS
ANYONE?

39. unless (x + y > 0) y else x

40. if
> yx
+ 0
x y

41. unless
> xy
+ 0
x y

42. if
> yx
+ 0
x y

43. every tree is a list ()
first element is the root
other elements are children
recur

44. if
> yx
+ 0
x y
(if …)

45. if
> yx
+ 0
x y
(if (> …) x y)

46. if
> yx
+ 0
x y
(if (> (+ …) 0) x y)

47. if
> yx
+ 0
x y
(if (> (+ x y) 0) x y)

49. CODE AS DATA

50. HOMOICONICITY

51. immutability, no side effects,
laziness, concurrency etc.

52. INTERACTIVITY

53. REPL
Read Evaluate Print Loop

54. DEMO