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Welcome to the world of the functional programming Kenta Murata 2011.06.11 #osc11doMonday, June 13, 2011 1

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mrkn Ruby Rubyhttp://www.flickr.com/photos/koichiroo/5244581973/Monday, June 13, 2011 3

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Monday, 12010 3 June 13, 2011 4

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Welcome to the world of the functional programming Kenta Murata 2011.06.11 #osc11doMonday, June 13, 2011 5

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Functional ProgrammingMonday, June 13, 2011 6

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Imperative Programming Procedural ProgrammingMonday, June 13, 2011 7

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Fortran Basic Cobol Algol C C++ Java LISPMonday, June 13, 2011 8

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Functional ProgrammingMonday, June 13, 2011 10

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High-order Functions Lazy EvaluationMonday, June 13, 2011 11

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Functions as Building Blocks for constructing programshttp://www.flickr.com/photos/stevendepolo/5597111652Monday, June 13, 2011 12

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Functions as Glue for bonding functionshttp://www.flickr.com/photos/pseudoego/5417919481Monday, June 13, 2011 13

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A lot of programming languages available for functional programminghttp://www.flickr.com/photos/32712959@N07/3222623206Monday, June 13, 2011 14

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High-order FunctionsMonday, June 13, 2011 18

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Haskell [ ] e.g. [] [1, 2, 3] (:) e.g. [1] => 1 : [] [1, 2, 3] => 1 : 2 : 3 : []Monday, June 13, 2011 21

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(:) LISP cons cons Haskell cons :: a -> [a] -> [a] -- cons x [] = [x] -- cons x1 (x2:xs) = x1 : (cons x2 xs)Monday, June 13, 2011 22

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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);Monday, June 13, 2011 23

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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]Monday, June 13, 2011 24

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(Int) sum sum :: [Int] -> Int sum [] = 0 sum (n:ns) = n + (sum ns)Monday, June 13, 2011 25

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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)Monday, June 13, 2011 26

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cons x [] = [x] sum [] = 0 cons x1 (x2:xs) = x1 : (cons x2 xs) sum (n :ns) = n + (sum ns)Monday, June 13, 2011 27

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(Int) product product :: [Int] -> Int product [] = 1 product (n:ns) = n * product nsMonday, June 13, 2011 28

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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)Monday, June 13, 2011 29

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(Bool) allTrue allTrue :: [Bool] -> Bool allTrue [] = True allTrue (b:bs) = b && allTrue nsMonday, June 13, 2011 30

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(Bool) anyTrue anyTrue :: [Bool] -> Bool anyTrue [] = False anyTrue (b:bs) = b || anyTrue nsMonday, June 13, 2011 31

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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)Monday, June 13, 2011 32

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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)Monday, June 13, 2011 32

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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 (||) FalseMonday, June 13, 2011 33

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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 (||) FalseMonday, June 13, 2011 33

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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 (||) FalseMonday, June 13, 2011 33

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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 (||) FalseMonday, June 13, 2011 33

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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]Monday, June 13, 2011 34

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Functions as Building Blocks for constructing programshttp://www.flickr.com/photos/stevendepolo/5597111652Monday, June 13, 2011 38

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Functions as Glue for bonding functionshttp://www.flickr.com/photos/pseudoego/5417919481Monday, June 13, 2011 39

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-- 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, :+)Monday, June 13, 2011 41

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Lazy EvaluationMonday, June 13, 2011 43

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http://www.sampou.org/haskell/article/whyfp.htmlMonday, June 13, 2011 46

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http://www.infoq.com/interviews/john-hughes-fpMonday, June 13, 2011 47

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http://weblog.raganwald.com/2007/03/why-why-functional-programming-matters.htmlMonday, June 13, 2011 48

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language evaluation pureness Haskell lazy pure Concurrent Clean lazy pure OCaml strict impure F# strict impure Scheme strict impureMonday, June 13, 2011 49

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language evaluation pureness Haskell lazy pure Concurrent Clean lazy pure OCaml strict impure F# strict impure Scheme strict impureMonday, June 13, 2011 50

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Monday, 12010 3 June 13, 2011 52

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Functional ProgrammingMonday, June 13, 2011 53

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A lot of programming languages available for functional programminghttp://www.flickr.com/photos/32712959@N07/3222623206Monday, June 13, 2011 54

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High-order FunctionsMonday, June 13, 2011 56

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

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Functions as Glue for bonding functionshttp://www.flickr.com/photos/pseudoego/5417919481Monday, June 13, 2011 58

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Lazy EvaluationMonday, June 13, 2011 59

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