Slide 1
Slide 1 text
Sunday, 7 October 12
Slide 2
Slide 2 text
Plan B
Sunday, 7 October 12
Slide 3
Slide 3 text
Why functional is the
new black
Elise Huard @elise_huard JSConf EU 2012
Sunday, 7 October 12
Slide 4
Slide 4 text
Why functional is the
new black
Elise Huard @elise_huard JSConf EU 2012
Sunday, 7 October 12
Slide 5
Slide 5 text
Why functional is the
new black
Elise Huard @elise_huard JSConf EU 2012
Sunday, 7 October 12
Slide 6
Slide 6 text
Sunday, 7 October 12
Slide 7
Slide 7 text
λ
λ
Sunday, 7 October 12
Slide 8
Slide 8 text
λ
λ
Sunday, 7 October 12
Slide 9
Slide 9 text
Sunday, 7 October 12
Slide 10
Slide 10 text
Sunday, 7 October 12
Slide 11
Slide 11 text
It’s all functions
Sunday, 7 October 12
Slide 12
Slide 12 text
It’s all functions
no global variables or global
state
Sunday, 7 October 12
Slide 13
Slide 13 text
It’s all functions
no global variables or global
state
no side-effects
Sunday, 7 October 12
Slide 14
Slide 14 text
It’s all functions
no global variables or global
state
no side-effects
no destructive updates
Sunday, 7 October 12
Slide 15
Slide 15 text
function Person(gender) {
this.gender = gender;
}
Person.prototype.sayGender = function()
{
console.log(this.gender);
};
var person1 = new Person('Male');
var genderTeller = person1.sayGender;
Sunday, 7 October 12
Slide 16
Slide 16 text
Sunday, 7 October 12
Slide 17
Slide 17 text
Some “patterns”
Sunday, 7 October 12
Slide 18
Slide 18 text
Higher order functions
Sunday, 7 October 12
Slide 19
Slide 19 text
Taking functions as
arguments
Sunday, 7 October 12
Slide 20
Slide 20 text
input.change(function(event) {...});
app.get('/', function(req, res) { ...});
Sunday, 7 October 12
Slide 21
Slide 21 text
returning functions
Sunday, 7 October 12
Slide 22
Slide 22 text
var validate = function(validationFunction) {
return function(field) {
var isError, errorMessage = validationFunction(field);
return (isError,errorMessage);
}
}
var requiredField = validate(function(field) {
var errorMessage = null;
if (!field) {
errorMessage = "should have a field"
}
return [!field, errorMessage];
})
Sunday, 7 October 12
Slide 23
Slide 23 text
Utilities
Sunday, 7 October 12
Slide 24
Slide 24 text
[1,3,5].map(function(x) {return x+1 });
http://underscorejs.org/
_.map([1,2,3], function(x) {return x+1});
http://osteele.com/sources/javascript/functional/
map('x+1', [1,2,3,4])
Sunday, 7 October 12
Slide 25
Slide 25 text
for (var i = 0; i < array.length; i++)
doSomething(array[i]); // => map
for (var i = 0; i < array.length; i++) {
if (array[i]%2 == 0)
doSomething(array[i]);
} // => filter
var sum = 0;
for (var i = 0; i < array.length; i++) {
sum += array[i];
} // => reduce/foldl
http://notes-on-haskell.blogspot.co.uk/2007/02/whats-wrong-with-for-loop.html
Sunday, 7 October 12
Slide 26
Slide 26 text
Currying
Sunday, 7 October 12
Slide 27
Slide 27 text
var phoneListing = function(name,home)
{
return name + “ - “ + phone;
}
listing(“Sam”,”012345678”);
listing(“Sam”); // => undefined
Sunday, 7 October 12
Slide 28
Slide 28 text
// getLocalArgs() = Array.prototype.slice.call(arguments)
function partial(f) {
var args = getLocalArgs(),
givenArgs = args.slice(1);
return function() {
var remainingArgs = getLocaLArgs();
return f.apply(this, givenArgs.concat(remainingArgs));
}
}
var samsPartner= partial(phoneListing, ”Sam”);
samsPartner(“0999999999”); // => “Sam - 0999999999”
Sunday, 7 October 12
Slide 29
Slide 29 text
Monads
Sunday, 7 October 12
Slide 30
Slide 30 text
Sunday, 7 October 12
Slide 31
Slide 31 text
// make a monadic value (“return”)
var makeMonadicValue = function(value) {
return function(state) {
return {value: value, state: state};
}
}
Sunday, 7 October 12
Slide 32
Slide 32 text
// make a very simple monadic value
var makeMonadicValue = function(value) {
return function() {
return value;
}
}
Sunday, 7 October 12
Slide 33
Slide 33 text
// make a monadic value (“return”)
var makeMonadicValue = function(value) {
return function(state) {
return {value: value, state: state};
}
}
Sunday, 7 October 12
Slide 34
Slide 34 text
// Joe is in the kitchen
var mv = makeMonadicValue("Joe");
mv(10); // => {value: "Joe", state: 10}
Sunday, 7 October 12
Slide 35
Slide 35 text
// bind to a function
var bindToFunction = function(mv, f) {
return function(state) {
var monadOutput = mv(state),
value = monadOutput.value,
newState = monadOutput.state;
return (f(value))(newState);
}
}
Sunday, 7 October 12
Slide 36
Slide 36 text
// you could act on the value directly
var addPerson = function(value, name) {
return value + " and " + name;
}
// but here's the monadic way to do it
var mAddPerson = function(mv, name) {
return bindToFunction(mv, function(value) {
return makeMonadicValue(value + " and " + name);
})
}
Sunday, 7 October 12
Slide 37
Slide 37 text
(mAddPerson(mv, "Tom"))(10);
// => {value:"Joe and Tom", state: 10}
Sunday, 7 October 12
Slide 38
Slide 38 text
// you can act on state
var takeYoghurt = function(state) {
return state - 1;
}
var mTakeYoghurt = function(mv) {
return bindToFunction(mv, function(value) {
return function(state) {
return {value: value, state: state-1};
}
})
}
(mTakeYoghurt(mv))(10); // => {value: "Joe", state: 9 }
Sunday, 7 October 12
Slide 39
Slide 39 text
(mTakeYoghurt(
(mAddPerson(
(mTakeYoghurt(
(mAddPerson
(mv,"Tom")
))),
"Shelley"))))
(10);
// => { value: 'Joe and Tom and
Shelley', state: 8 }
http://www.infoq.com/presentations/Why-is-a-Monad-Like-a-
Writing-Desk
Sunday, 7 October 12
Slide 40
Slide 40 text
Lazy evaluation (?)
Sunday, 7 October 12
Slide 41
Slide 41 text
The Good
Sunday, 7 October 12
Slide 42
Slide 42 text
Easier to debug
Sunday, 7 October 12
Slide 43
Slide 43 text
Easier to test
Sunday, 7 October 12
Slide 44
Slide 44 text
Easier to refactor
Sunday, 7 October 12
Slide 45
Slide 45 text
Parallelization (?)
Sunday, 7 October 12
Slide 46
Slide 46 text
Hard?
Sunday, 7 October 12
Slide 47
Slide 47 text
Sunday, 7 October 12
Slide 48
Slide 48 text
"the greatest single programming
language ever designed"
- Alan Kay, on Lisp, the 70s
Sunday, 7 October 12
Slide 49
Slide 49 text
“Object-oriented programming
(...) allows software structure to
be based on real-world structures,
and gives programmers a powerful
way to simplify the design and
construction of complex programs.
- D. Gelernter, the 80s
Sunday, 7 October 12
Slide 50
Slide 50 text
Sunday, 7 October 12
Slide 51
Slide 51 text
Software is hard
Sunday, 7 October 12
Slide 52
Slide 52 text
Sunday, 7 October 12
Slide 53
Slide 53 text
Sunday, 7 October 12
Slide 54
Slide 54 text
But:
Sunday, 7 October 12
Slide 55
Slide 55 text
Thank you.
Elise Huard @elise_huard
Sunday, 7 October 12