functional programming for fun and profit

FUNCTIONALPROGRAMMING

function() { return [‘fun’,‘profit’];}

Monday, 28 October 13

James Ottaway

@jms_

Monday, 28 October 13

elevator pitch

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teaser examples

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(take 25 (squares-of (integers)))

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[‘1’,’2’,’3’,’4’].map(&:to_i).reduce(&:+)

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[1,2,3,4,5].filter(function(i) { return i % 2 == 0;});

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history

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lambda calculus

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declarative programming

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> how

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nested paradigmsMonday, 28 October 13

regex

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reactive programming

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domain specific languages

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functional programming

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languages

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concepts

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function() { }

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function counter() { var x = 0;

function increment(y) { x += y; console.log(x); }

return increment;}

closures

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first_counter = counter();second_counter = counter();

first_counter(1) // returns 1first_counter(2) // returns 3first_counter(3) // returns 6

second_counter(5) // returns 5second_counter(5) // returns 10second_counter(5) // returns 15

closures

Monday, 28 October 13

no side effects

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insanity

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ONE = 1;

add = lambda { |x, y| x + y}

addOne = lambda { |x| add[x, ONE]}

referential transparency

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require 'date'

opaque_millis = lambda { DateTime.now.strftime('%Q').to_i}

transparent_millis = lambda { |datetime| datetime.strftime('%Q').to_i}

referential transparency

Monday, 28 October 13

memoisation

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deforestationMonday, 28 October 13

state is inevitable

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recursion

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structure and interpretation of computer programs

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examples

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list comprehension

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source = [1,2,3,4,5]destination = []

for i in 0..source.length-1 do destination << source[i]*2end

return destination

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[1,2,3,4,5].map { |i| i * 2 }

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numbers = [1,2,3,4,5]x = 0

for i in 1..numbers.length-1 do x += numbers[i]end

return x

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[1,2,3,4,5].reduce { |acc, x| acc + x }

Monday, 28 October 13

[1,2,3,4,5].reduce(&:+)

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mobile app frameworks

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Monday, 28 October 13

programming with nothing

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reactive extensions

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github desktop clients

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go forth and prosper!

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thanks

Monday, 28 October 13