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![27 File.open("/tmp/setec_astronomy", "w") do |f| # do stuff with f end [1, 2, 3].map do |i| i + 1 end # => [2, 3, 4]](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-27-2048.jpg)
![28 // take a function as an argument let callMeMaybe = function (f) { if (Math.random() < 0.5) { return f(); } else { return undefined; } } for (var i of [1, 2, 3, 4, 5]) { console.log(`Try ${i}`); callMeMaybe(function () { console.log("I GOT CALLED!"); }); }](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-28-2048.jpg)
![32 let coll = [1, 2, 3, 4, 5]; let result = reduce(coll, 0, function (i, sum) { return sum + i; }); console.log(result); // => 15](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-32-2048.jpg)
![33 let reduce = function (coll, acc, fn) { if (coll.length === 0) { return acc; } let head = coll[0]; let rest = coll.slice(1, coll.length); let newAcc = fn(head, acc); return reduce(rest, newAcc, fn); }](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-33-2048.jpg)
![35 let coll = [1, 2, 3, 4, 5]; let result = map(coll, function (i) { return i + 1; }); console.log(result); // => [2, 3, 4, 5, 6]](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-35-2048.jpg)
![36 let map = function (coll, fn) { return reduce(coll, [], function (i, acc) { return acc.concat(fn(i)); }); }](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-36-2048.jpg)
![38 let coll = [1, 2, 3, 4, 5]; let result = filter(coll, function (i) { return i < 4; }); console.log(result); // => [1, 2, 3]](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-38-2048.jpg)
![39 let filter = function (coll, fn) { return reduce(coll, [], function (i, acc) { if (fn(i)) { return acc.concat(i); } else { return acc; } }); }](https://image.slidesharecdn.com/introtofunctional-150522033653-lva1-app6892/75/Functional-Programming-An-Introduction-39-2048.jpg)
Functional Programming: An Introduction
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- 2. > Drew Olson >Braintree > github.com/drewolson 2
- 3. Things to know >Ask questions > node > babeljs.io 3
- 4. Reduce/Map/Filter in Javascript 4 WithoutState Without Mutation
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- 6. What are wegoing to focus on? > Immutability > No state > Higher-order functions > Lots of code 6
- 7. What aren’t wegoing to focus on? > Types > Monads > Being tricky to feel smart 7
- 8. Why even care? >Explicitness > Concurrency / Parallelism > Understandability 8
- 9. Reduce/Map/Filter in Javascript 9 WithoutState > Without Mutation
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- 11. 11 let a = 1; a = 2; console.log(a); // => 2 //:( Enforced via discipline :)
- 12. Reduce/Map/Filter in Javascript 12 >Without State Without Mutation
- 13. 13 class Foo attr_accessor :bar def initialize(bar) @bar = bar end def increment(i) i + 1 end end foo= Foo.new(1) # things happen here # . # .. # ... # what does this return? p foo.bar # what does this return? p foo.increment(2)
- 14. Let’s add somenumbers! 14
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- 17. Recursion! > Base case >Recursive call 17
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- 20. 20 // sumRec(5) // 1+ sumRec(4) // 1 + (1 + sumRec(3)) // 1 + (1 + (1 + sumRec(2))) // 1 + (1 + (1 + (1 + sumRec(1)))) // 1 + (1 + (1 + (1 + (1 + sumRec(0))))) // 1 + (1 + (1 + (1 + (1 + 0)))) // 1 + (1 + (1 + (1 + 1))) // 1 + (1 + (1 + 2)) // 1 + (1 + 3) // 1 + 4 // 5
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- 22. 22 // sumTail(5) // sumTail(5,0) // sumTail(4, 1) // sumTail(3, 2) // sumTail(2, 3) // sumTail(1, 4) // sumTail(0, 5) // 5
- 23. > Reduce/Map/Filter in Javascript23 Without State Without Mutation
- 24. Higher-order functions! > Functionsas values > Take functions as input > Return functions 24
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- 26. Higher-order functions! YOU KNOWTHIS!! 26
- 27. 27 File.open("/tmp/setec_astronomy", "w") do |f| # do stuffwith f end [1, 2, 3].map do |i| i + 1 end # => [2, 3, 4]
- 28. 28 // take afunction as an argument let callMeMaybe = function (f) { if (Math.random() < 0.5) { return f(); } else { return undefined; } } for (var i of [1, 2, 3, 4, 5]) { console.log(`Try ${i}`); callMeMaybe(function () { console.log("I GOT CALLED!"); }); }
- 29. 29 Try 1 I GOTCALLED! Try 2 Try 3 I GOT CALLED! Try 4 I GOT CALLED! Try 5
- 30. 30 // return afunction let incrementor = function (n) { return function (i) { return i + n; } } let add1 = incrementor(1); console.log(add1(2)); // => 3
- 31. OK! Let’s implementreduce! > Tail recursion > Higher-order functions > No state > No mutation 31
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- 34. OK! Let’s implementmap! > ONLY USING REDUCE!!?!??! 34
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- 36.
- 37. OK! Let’s implementfilter! > ONLY USING REDUCE!!?!??! > This time less shockingly revealed!! 37
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- 40. Reduce/Map/Filter in Javascript 40 WithoutState Without Mutation
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- 42. Things to checkout > Functional Javascript (book) > The Little Schemer (book) > Elixir (language) 42
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