Programação Funcional FISL 2013

1. Programação Funcional
FISL 2013
Juarez Bochi
λ
Sunday, July 14, 13

2. Juarez Bochi
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3. Juarez Bochi
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4. Juarez Bochi
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5. Juarez Bochi
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6. Juarez Bochi
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7. Agenda
• Motivação
• Conceitos
• Exemplos
• Resumo
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8. Motivação
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9. Ler um arquivo, listar
as palavras mais
comuns em ordem
decrescente.
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10. Ler um arquivo, listar
as palavras mais
comuns em ordem
decrescente.
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11. Donald Knuth
X
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12. Donald Knuth Doug McIlroy
X
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13. Donald Knuth Doug McIlroy
X
10+ páginas de Pascal/WEB
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14. Donald Knuth Doug McIlroy
X
10+ páginas de Pascal/WEB 6 linhas de shell
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15. tr -cs A-Za-z 'n' |
tr A-Z a-z |
sort |
uniq -c |
sort -rn |
sed ${1}q
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16. Sunday, July 14, 13

17. $ cat discurso.txt | tr -cs A-Za-z 'n' | tr A-Z a-z | sort |
uniq -c | sort -rn | sed 40q
65 e
48 de
42 a
35 o
32 que
18 os
15 para
15 com
14 mais
13 nao
13 do
11 as
10 um
10 dos
10 da
9 das
8 ela
7 todos
7 se
7 pais
7 muito
6 ruas
6 brasil
5 violencia
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18. “Keep it simple, make
it general, and make it
intelligible.”
Doug McIlroy
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19. “Keep it simple, make
it general, and make it
intelligible.”
Doug McIlroy
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20. Conceitos
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21. Paradigmas
• Imperativo
• Lógico
• Funcional
• Orientado a Objetos
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22. Paradigma Imperativo
Linguagem Computador
Variáveis Mutáveis Endereço de memória
Estruturas de controle
(if-then-else, loop)
Jumps
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23. “Can Programming Be
Liberated from the von.
Neumann Style?”
John Backus - Turing Award Lecture
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24. Programação Funcional
• Concentrar em teorias, não mutações
• Minimizar mudança de estados
• Sem estruturas de controle
imperativas
• Foco em funções
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25. “Programação Funcional
é ortogonal à Orientação
a Objetos”
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26. Elementos de Programação
• Expressões Primitivas
• Meios de Combinação
• Meios de Abstração
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27. Exemplos
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28. First Class Functions
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29. First Class Functions
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30. Closure
> var inc, dec;
undefined
> function contador() {
... var x = 0;
... inc = function() { return ++x; };
... dec = function() { return --x; };
... }
undefined
> contador();
undefined
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31. Closure
> inc();
1
> inc();
2
> dec();
1
> dec();
0
> inc();
1
> x
ReferenceError: x is not defined
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32. > import Control.Applicative
> let foo = fmap (+3) (+2)
> foo 10
15
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33. > import Control.Applicative
> let foo = fmap (+3) (+2)
> foo 10
15
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34. > (defn soma3 [x] (+ x 3))
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35. > (defn soma3 [x] (+ x 3))
> (map soma3 [2 4 6])
(5 7 9)
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36. > (defn soma3 [x] (+ x 3))
> (map soma3 [2 4 6])
(5 7 9)
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37. > (defn soma3 [x] (+ x 3))
> (map soma3 [2 4 6])
(5 7 9)
> (pmap soma3 [2 4 6])
(5 7 9)
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38. Higher Order Function
pessoas = [{'nome': 'Adolfo', 'estado': 'MG'},
{'nome': 'Pedro', 'estado': 'RS'},
{'nome': 'Maria', 'estado': 'AC'}]
def por_estado(pessoa1, pessoa2):
return cmp(pessoa1['estado'], pessoa2['estado'])
>>> pprint.pprint(sorted(pessoas, cmp=por_estado))
[{'estado': 'AC', 'nome': 'Maria'},
{'estado': 'MG', 'nome': 'Adolfo'},
{'estado': 'RS', 'nome': 'Pedro'}]
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39. Recursão
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40. Recursão
(define (fib n)
.. (if (< n 2)
.. n
.. (+ (fib (- n 1)) (fib (- n 2)))))
(fib 10)
=> 55
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41. Tail Call Optimization
1. fib(5)
2. fib(4) + fib(3)
3. (fib(3) + fib(2)) + (fib(2) + fib(1))
4. ((fib(2) + fib(1)) + (fib(1) + fib(0))) + ((fibb(1) + fib(0)) + fib(1))
5. (((fib(1) + fib(0)) + fib(1)) + (fib(1) + fib(0))) + ((fib(1) + fib(0)) +
fib(1))
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42. Tail Call Optimization
(define (fib n)
.. (letrec ((fib-aux (lambda (n a b)
.. (if (= n 0)
.. a
.. (fib-aux (- n 1) b (+ a b))))))
.. (fib-aux n 0 1)))
(fib 1000)
=> 4.346655768693743e+208
1. fib(5)
2. fib(4) + fib(3)
3. (fib(3) + fib(2)) + (fib(2) + fib(1))
4. ((fib(2) + fib(1)) + (fib(1) + fib(0))) + ((fibb(1) + fib(0)) + fib(1))
5. (((fib(1) + fib(0)) + fib(1)) + (fib(1) + fib(0))) + ((fib(1) + fib(0)) +
fib(1))
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43. Sunday, July 14, 13

44. Currying & Partials
def to_tag(tag, texto):
return "<{tag}>{texto}</{tag}>".format(tag=tag,
texto=texto)
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45. Currying & Partials
def partial(funcao, argumento):
def fn(arg):
return funcao(argumento, arg)
return fn
def to_tag(tag, texto):
return "<{tag}>{texto}</{tag}>".format(tag=tag,
texto=texto)
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46. Currying & Partials
def partial(funcao, argumento):
def fn(arg):
return funcao(argumento, arg)
return fn
def to_tag(tag, texto):
return "<{tag}>{texto}</{tag}>".format(tag=tag,
texto=texto)
negrito = partial(to_tag, 'b')
italico = partial(to_tag, 'i')
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47. Currying & Partials
def partial(funcao, argumento):
def fn(arg):
return funcao(argumento, arg)
return fn
def to_tag(tag, texto):
return "<{tag}>{texto}</{tag}>".format(tag=tag,
texto=texto)
negrito = partial(to_tag, 'b')
italico = partial(to_tag, 'i')
>>> negrito(italico("Oi, FISL!"))
"<b><i>Oi FISL!</i></b>"
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48. Currying & Partials
def partial(funcao, argumento):
def fn(arg):
return funcao(argumento, arg)
return fn
def to_tag(tag, texto):
return "<{tag}>{texto}</{tag}>".format(tag=tag,
texto=texto)
DSL!!
negrito = partial(to_tag, 'b')
italico = partial(to_tag, 'i')
>>> negrito(italico("Oi, FISL!"))
"<b><i>Oi FISL!</i></b>"
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49. Laziness
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50. Laziness
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51. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
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52. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
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53. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
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54. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
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55. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
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56. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
s.head #:: sieve(s.tail filter (_ % s.head != 0))
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57. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
s.head #:: sieve(s.tail filter (_ % s.head != 0))
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58. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
s.head #:: sieve(s.tail filter (_ % s.head != 0))
val primes = sieve(from(2))
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59. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
s.head #:: sieve(s.tail filter (_ % s.head != 0))
val primes = sieve(from(2))
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60. Laziness
def from(n: Int): Stream[Int] = n #:: from(n+1)
val nats = from(0)
def sieve(s: Stream[Int]): Stream[Int] =
s.head #:: sieve(s.tail filter (_ % s.head != 0))
val primes = sieve(from(2))
(primes take N).toList
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61. Data Abstraction
class Zero(Natural):
def __init__(self):
pass
def __repr__(self):
return "0"
def __add__(self, other):
return other
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62. Data Abstraction
class Zero(Natural):
def __init__(self):
pass
def __repr__(self):
return "0"
def __add__(self, other):
return other
class Natural(object):
def __init__(self, anterior):
self.anterior = anterior
def __repr__(self):
return repr(self.anterior) + " + 1"
def __add__(self, other):
return self.anterior + other.sucessor()
def sucessor(self):
return Natural(anterior=self)
Sunday, July 14, 13

63. Data Abstraction
class Zero(Natural):
def __init__(self):
pass
def __repr__(self):
return "0"
def __add__(self, other):
return other
class Natural(object):
def __init__(self, anterior):
self.anterior = anterior
def __repr__(self):
return repr(self.anterior) + " + 1"
def __add__(self, other):
return self.anterior + other.sucessor()
def sucessor(self):
return Natural(anterior=self)>>> zero = Zero()
>>> um = zero.sucessor()
>>> dois = um.sucessor()
>>> um
0 + 1
>>> dois
0 + 1 + 1
>>> um + dois
0 + 1 + 1 + 1
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64. Resumo
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65. Blub Paradox
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66. Resumo
Código fácil de entender
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67. Resumo
Código fácil de manter
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68. Resumo
Código fácil de testar
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69. Resumo
Código fácil de escalar
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70. Obrigado!
@jbochi
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71. Referências
• http://www.leancrew.com/all-this/2011/12/more-shell-less-egg/
• http://onesixtythree.com/literate/literate2.pdf
• http://mitpress.mit.edu/sicp/
• http://www.paulgraham.com/avg.html
• https://www.coursera.org/course/progfun
• http://www.slideshare.net/jbochi/programao-funcional-em-python
• https://raw.github.com/richhickey/slides/master/simplicitymatters.pdf
• http://pragprog.com/magazines/2013-01/functional-programming-basics
• http://adit.io/posts/2013-04-17-functors,_applicatives,_and_monads_in_pictures.html
• http://en.literateprograms.org/Fibonacci_numbers_(Scheme)
• http://norvig.com/21-days.html
• http://www.youtube.com/watch?v=3jg1AheF4n0
• http://www.flickr.com/photos/niceric/74977685/sizes/l/in/
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