1. Ihome In Action Author:Dennis IHOME

2. FP

FP Functional Programming

lambda

Lambda

Alonzo Church Stephen Cole Kleene 20 30

3. FP

Lambda

1 Erlang

2

amb

Less Code

4. FP

currying Continuation

Mond

5.

1 final

2 erlang

3

6.

scheme procedure

+=>#

(define (square x) (* x x)

(square 3)=> 9

(square 4)=> 10

( (lambda(x) (* x x))3)=> 9

high-order function FP first-class

7.

Map foreach filter

map, proc

(define (map proc items)

(if (null? Items)

'()

(cons (proc (car items))

(map proc (cdr items)))))

(map square (list 1 2 3 4))

=> (1 4 9 16)

8. filter

,predicate

(define (filter predicate sequence)

(cond ((null? sequence) '())

((predicate (car sequence))

(cons (car sequence) (filter predicate (cdr sequence))))

(else

(filter predicate (cdr sequence)))))

9. accumulate

OP

(define (accumulate op initial sequence)

(if (null? sequence)

initial

(op (car sequence) (accumulate op initial (cdr sequence)))))

10.

,

low high)

'()

(cons low (enumerate-interval (+ low 1) high))))

(enumerate-interval 0 n)

11.

map0-nfib(k)

(map fib (enumerate-interval 0 n))

(filter even?

(map fib (enumerate-interval 0 n)))

12.

(accumulate cons

'()

(filter even?

(map (enumerate-interval 0 n)))))

13.

(define (even-fibs n)

(accumulate cons

'()

(filter even?

(map fib (enumerate-interval 0 n)))))

14.

15. -

block

(define (get-adder x)

(lambda(y)(+ x y)))

X get-adder

(define add4 (get-adder 4))

(add4 7)=> 11

16. -

Java:

class Product implements Comparator{

public int compare(Product other)

return this.price-other.price

Collections.sort(products)

Ruby:

products.sort{|a,b| a.price-b.price}

17. -

Java7

double log = { double x => Math.log(x) }.invoke(10);

int sum = { int x, int y => x + y }.invoke(3, 4); // will return 7

String[] girls = { "Jane", "Eva", "Sarah", "Alice" };

Arrays.sort(girls, { String s1, String s2 => int r = s1.length() - s2.length(); r == 0 ? s1.compareTo(s2) : r });

18.

lua:

function make_stack()

local data = {}; local last = -1;

local function push(e) last = last + 1; data[last] = e; end

local function pop() if last == -1 then return nil end last = last - 1 return data[last+1] end

return function (index) local tb = {push=push, pop=pop} return tb[index] end end

s=make_stack()

s("push")("test0")

s("push")("test1") s("push")("test2") s("push")("test3")

print(s("pop")()) print(s("pop")()) print(s("pop")())

19. Currying

Currying Haskell Curry lambda curry

20. Currying 1

Javascript

functionadd(x,y) {if(x!=null&&y!=null)returnx+y;

elseif(x!=null&&y==null)

returnfunction(y) {returnx+y;}

elseif(x==null&&y!=null)

returnfunction(x){returnx+y;}}

vara=add(3,4);

varb=add(2);

varc=b(10);

21. Currying 2

Ruby1.9 Proc#curry

plus=lambda{|a,b|a+b}

plus(3,4)=>7

curried_plus=plus.curry

plus_three=curried_plus[3]

plus_three(4)=>7

22. Currying 3

is_weekday=lambda{|day_of_week,time|time.wday==day_of_week}.curry

sunday=is_weekday[0]

monday=is_weekday[1]

tuesday=is_weekday[2]

wednesday=is_weekday[3]

thursday=is_weekday[4]

friday=is_weekday[5]

saturday=is_weekday[6]

caseTime.now

whensunday

puts"Dayofrest"

whenmonday,tuesday,wednesday,thursday,friday

puts"Work"

whensaturday

puts"chores"

end

23.

Lazy evalution

1

2 (stream)

24.

Unless

(define (unless condition usual-value exception-value)

(if condition

Exception-value

Usual-value))

(unless (= 0 0)

(/ 1 0)

(begin (display exception return 0) 0))

25.

(/ 1 0)

(= 0 0)trueexception-value(/ 1 0)

26.

conscarcdrstream-cons stream-car stream-cdrstream-map stream-filter

:(define (integers-starting-from n)

(cons-stream n (integers-starting-from (+ n1))))

(define integers (integers-starting-from 1))

27.

1

(define ones (cons-stream 1 ones))

28.

(define (divisible? x y) (= (remainder x y) 0))

(define (sieve stream)

(cons-stream

(stream-car stream)

(sieve (stream-filter (lambda(x)

(not (divisible? x (stream-car stream))))

(stream-cdr stream)))))

(define primes (sieve (integers-starting-from 2)))

29. Continuation

1 what to evalute?

2 waht to do with the value?

what to do with the value (continuation)

30. Continuation

(if (null? x)

'()

(cdr x))

(null? x)'()(cdr x)(null? x).

(+ 2

(call/cc

(lambda (k)

(* 5 (k 4)))))=> 6

31. Continuation

call/cc:call-with-current-continuation

continuation

SchemeRubycall/cc

Continuaton

1breakgoto

2

3failtry

32. Continuation break

schemebreakcontinuation

(define product

(lambda (ls)

(call/cc

(lambda (break)

(let f ((ls ls))

(cond

((null? ls) 1)

((= (car ls) 0) (break 0))

(else (* (car ls) (f (cdr ls))))))))))

33. Continuation amb

amb, John McCarthy 1961

Amb

amb e1 e2 e3 e4 ...)

n ei

(list (amb 1 2 3) (amb 'a 'b))

(1 a) (1 b)(2 a) (2 b)(3 a) (3 b)

(amb) fail

(define (require p)

(if (not p) (amb)))

34. amb

call/ccambcontinuation

scheme continuation 2.scm

Rubycontinuation.rb

35. amb

:

Baker, Cooper, Fletcher, Miller, Smith5BakerCooperFletcherMillerCooperSmithFletcherFletcherCooper

36.