1.
Welcome to the world of the functional programming
Kenta Murata 2011.06.11 #osc11do
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2.
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3.
mrkn
Ruby
Ruby
http://www.flickr.com/photos/koichiroo/5244581973/
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4.
Monday, 1
2010 3 June 13, 2011 4

5.
Welcome to the world of the functional programming
Kenta Murata 2011.06.11 #osc11do
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6.
Functional Programming
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7.
Imperative Programming
Procedural Programming
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8.
Fortran
Basic
Cobol
Algol
C
C++
Java
LISP
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9.
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10.
Functional Programming
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11.
High-order Functions
Lazy Evaluation
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12.
Functions
as Building Blocks
for constructing programs
http://www.flickr.com/photos/stevendepolo/5597111652
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13.
Functions as Glue
for bonding functions
http://www.flickr.com/photos/pseudoego/5417919481
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14.
A lot of programming
languages
available for
functional programming
http://www.flickr.com/photos/32712959@N07/3222623206
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15.
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16.
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17.
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18.
High-order Functions
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19.
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20.
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21.
Haskell [ ]
e.g. []
[1, 2, 3]
(:)
e.g. [1] => 1 : []
[1, 2, 3] => 1 : 2 : 3 : []
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22.
(:) LISP
cons
cons Haskell
cons :: a -> [a] -> [a] --
cons x [] = [x] --
cons x1 (x2:xs) = x1 : (cons x2 xs)
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23.
cons :: a -> [a] -> [a] --
cons x [] = [x] --
cons x1 (x2:xs) = x1 : (cons x2 xs)
// C++
template <typename a>
std::list<a>
cons(a const& x, std::list<a> const& xs);
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24.
cons :: a -> [a] -> [a] --
cons x [] = [x] --
cons x1 (x2:xs) = x1 : (cons x2 xs)
e.g. cons 0 [1,2,3,4]
=> x1 0, x2 1, xs [2,3,4]
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25.
(Int)
sum
sum :: [Int] -> Int
sum [] = 0
sum (n:ns) = n + (sum ns)
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26.
cons sum
cons :: a -> [a] -> [a]
cons x [] = [x]
cons x1 (x2:xs) = x1 : (cons x2 xs)
sum :: [Int] -> Int
sum [] = 0
sum (n:ns) = n + (sum ns)
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27.
cons x [] = [x]
sum [] = 0
cons x1 (x2:xs) = x1 : (cons x2 xs)
sum (n :ns) = n + (sum ns)
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28.
(Int)
product
product :: [Int] -> Int
product [] = 1
product (n:ns) = n * product ns
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29.
cons x [] = [x]
sum [] = 0
product [] = 1
cons x1 (x2:xs) = x1 : (cons x2 xs)
sum (n :ns) = n + (sum ns)
product (n :ns) = n * (product ns)
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30.
(Bool)
allTrue
allTrue :: [Bool] -> Bool
allTrue [] = True
allTrue (b:bs) = b && allTrue ns
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31.
(Bool)
anyTrue
anyTrue :: [Bool] -> Bool
anyTrue [] = False
anyTrue (b:bs) = b || anyTrue ns
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32.
cons x [] = [x]
sum [] = 0
product [] = 1
allTrue [] = True
anyTrue [] = False
cons x1 (x2:xs) = x1 : (cons x2 xs)
sum (n :ns) = n + (sum ns)
product (n :ns) = n * (product ns)
allTrue (b :bs) = b && (allTrue bs)
anyTrue (b :bs) = b || (anyTrue bs)
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33.
cons x [] = [x]
sum [] = 0
product [] = 1
allTrue [] = True
anyTrue [] = False
cons x1 (x2:xs) = x1 : (cons x2 xs)
sum (n :ns) = n + (sum ns)
product (n :ns) = n * (product ns)
allTrue (b :bs) = b && (allTrue bs)
anyTrue (b :bs) = b || (anyTrue bs)
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34.
reduce :: (a -> [a] -> a) -> a -> [a] -> a
reduce f x0 [] = x0
reduce f x0 (x1:xs) = f x1 (reduce f x0 xs)
sum = reduce (+) 0
product = reduce (*) 1
allTrue = reduce (&&) True
anyTrue = reduce (||) False
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35.
reduce :: (a -> [a] -> a) -> a -> [a] -> a
reduce f x0 [] = x0
reduce f x0 (x1:xs) = f x1 (reduce f x0 xs)
sum = reduce (+) 0
product = reduce (*) 1
allTrue = reduce (&&) True
anyTrue = reduce (||) False
Monday, June 13, 2011 33

36.
reduce :: (a -> [a] -> a) -> a -> [a] -> a
reduce f x0 [] = x0
reduce f x0 (x1:xs) = f x1 (reduce f x0 xs)
sum = reduce (+) 0
product = reduce (*) 1
allTrue = reduce (&&) True
anyTrue = reduce (||) False
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37.
reduce :: (a -> [a] -> a) -> a -> [a] -> a
reduce f x0 [] = x0
reduce f x0 (x1:xs) = f x1 (reduce f x0 xs)
sum = reduce (+) 0
product = reduce (*) 1
allTrue = reduce (&&) True
anyTrue = reduce (||) False
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38.
cons reduce
append :: [a] -> [a] -> [a]
append xs ys = reduce (:) ys xs
append [1,2] [3,4]
-> reduce (:) [3,4] [1,2]
-> reduce (:) [3,4] (1:2:[])
-> 1 : (reduce (:) [3,4] (2:[]))
-> 1 : 2 : (reduce (:) [3,4] [])
-> 1 : 2 : [3,4]
-> [1,2,3,4]
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39.
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40.
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41.
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42.
Functions
as Building Blocks
for constructing programs
http://www.flickr.com/photos/stevendepolo/5597111652
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43.
Functions as Glue
for bonding functions
http://www.flickr.com/photos/pseudoego/5417919481
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44.
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45.
-- Haskell
reduce (+) 0 [1..10]
// C++
int ns[] = {1,2,3,4,5,6,7,8,9,10};
std::accumulate(ns, ns + 10, 0, &std::plus<int>);
# Ruby
[*1..10].inject(0, :+)
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46.
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47.
Lazy Evaluation
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48.
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49.
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50.
http://www.sampou.org/haskell/article/whyfp.html
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51.
http://www.infoq.com/interviews/john-hughes-fp
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52.
http://weblog.raganwald.com/2007/03/why-why-functional-programming-matters.html
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53.
language evaluation pureness
Haskell lazy pure
Concurrent Clean lazy pure
OCaml strict impure
F# strict impure
Scheme strict impure
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54.
language evaluation pureness
Haskell lazy pure
Concurrent Clean lazy pure
OCaml strict impure
F# strict impure
Scheme strict impure
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55.
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56.
Monday, 1
2010 3 June 13, 2011 52

57.
Functional Programming
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58.
A lot of programming
languages
available for
functional programming
http://www.flickr.com/photos/32712959@N07/3222623206
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59.
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60.
High-order Functions
Monday, June 13, 2011 56

61.
Functions
as Building Blocks
for constructing programs
http://www.flickr.com/photos/stevendepolo/5597111652
Monday, June 13, 2011 57

62.
Functions as Glue
for bonding functions
http://www.flickr.com/photos/pseudoego/5417919481
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63.
Lazy Evaluation
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64.
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