Ramda JS como alternativa a underscore e lodash

1. Globalcode – Open4education
Ramda
Derek Stavis
Software Engineer

2. Globalcode – Open4education
Who?
Derek Stavis
github.com/derekstavis
Software Engineer
Ruby, JavaScript, Python, C
Node, React & Webpack Advocate

3. Globalcode – Open4education
Have you been using functional
helper libraries?

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Underscore?
🤔

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Lodash?
🤔

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Really?
🙄

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Those are really good libraries

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Weren't designed with a functional
mindset from day 0

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Ramda
A functional programming library
http://ramdajs.com

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Meet Ramda
Emphasizes a purer functional style
Immutability and side-effect free functions
Ramda functions are automatically curried
Argument ordering convenient to currying
Keep rightmost the data to be operated

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Small, single-responsibility and
reusable functions

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Ramda shines on currying

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Ramda shines on currying
var names = [
{ name: 'Pablo' },
{ name: 'Escobar' },
{ name: 'Gaviria' }
]
var getName = R.prop('name')
var pickNames = R.map(getName, names)
pickNames()
=> [ 'Pablo', 'Escobar', 'Gaviria' ]

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Ramda shines on currying
var names = [
{ name: 'Pablo' },
{ name: 'Escobar' },
{ name: 'Gaviria' }
]
var getName = R.prop('name')
var pickNames = R.map(getName)
pickNames(names)
=> [ 'Pablo', 'Escobar', 'Gaviria' ]

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Currying?
😨

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Currying was named after
Haskell Curry
One of the first to investigate such technique

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Turn a function that expects
multiple arguments into one that,
when supplied fewer arguments,
returns a new function that awaits
the remaining ones

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Ramda is about currying
const cookPasta = R.curry((water, heat, pasta) => { ... })
// Have everything needed
cookPasta (water, heat, pasta)
// Forgot to buy pasta
cookPasta (water, heat)(pasta)
// No gas and no pasta
cookPasta (water)(heat, pasta)
// Had to go twice to supermarket
cookPasta (water)(heat)(pasta)

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This is truly powerful

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Ramda is all curried
😎

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Point-free programming
🖖

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Ramda is all curried
R.add(2, 3) //=> 5
R.add(7)(10) //=> 17
R.contains(2, [1, 2, 3]) //=> true
R.contains(1)([1, 2, 3]) //=> true
R.replace(/foo/g, 'bar', 'foo foo') //=> 'bar bar'
R.replace(/foo/g, 'bar')('foo foo') //=> 'bar bar'
R.replace(/foo/g)('bar')('foo foo') //=> 'bar bar'

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Apply the parameters left-to-right
when you have them
👉

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But what if you'd like to apply the
leftmost or intermediate arguments
before the rightmost?

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Leave argument placeholders
✍

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Functional placeholder
R.minus(R.__, 5)(10) //=> 5
R.divide(R.__, 5)(10) //=> 17
R.contains(R.__, [1, 2, 3])(2) //=> true
R.contains(R.__, [1, 2, 3])(1) //=> true
R.contains(R.__, R.__)(1)([1, 2, 3]) //=> true

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Or do partial application

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Ramda does partial application
both left-to-right and right-to-left

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In fact, there's no currying as in
theoretical math, Ramda currying
is, in reality, partial application

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Partial application
const greet = (salutation, title, name) =>
`${salutation}, ${title} ${name}!`
const greetMrCrowley = R.partialRight(greet, ['Mr.', 'Crowley'])
greetMrCrowley('Hello') //=> 'Hello, Mr. Crowley!'
const greetMr = R.partial(greet, ['Hello', 'Mr.'])
const greetMs = R.partial(greet, ['Hello', 'Ms.'])
greetMr('Mendel') // => 'Hello, Mr. Mendel'
greetMs('Curie') // => 'Hello, Ms. Curie'

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Ramda also makes available some
cool and very useful functions

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Avoiding you to rewrite the same
stuff that you always have to

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Ramda functions are divided into
various categories

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Ramda functions categories
Function
Math
List
Logic
Object
Relation

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Function functions
// Always return the same thing, ignoring arguments
const name = R.always('Derek')
name('Willian') //=> Derek
// Functional if then else, a.k.a. Maybe Monad
const findName = R.ifElse(
R.has('name'),
R.prop('name'),
R.always('No name')
)
findName({ title: 'Mr.', name: 'Derek' }) //=> Derek
findName({ title: 'Mr.' }) //=> No name
// Pipe functions left-to-right. First function can have any arity
// Others must have arity of exactly one
const calculate = R.pipe(Math.pow, R.negate, R.inc);
calculate(3, 2); // -(3^2) + 1

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Math functions
// Addition
R.add(1, 2) //=> 3
// Subtraction
R.subtract(2, 1) //=> 1
// Sum all elements
R.sum([1, 1, 1]) //=> 3
// Increment
R.inc(41) //=> 42
// Decrement
R.dec(43) //=> 42
// Calculate the mean
R.mean([2, 7, 9]) //=> 6

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List functions
// Check if all elements match a predicate
R.all(R.gt(4), [1, 2, 3]) //=> true
// Check if a number is inside a list
R.contains(3, [1, 2, 3])
// Drop elements from start
R.drop(1, ['foo', 'bar', 'baz']) //=> ['bar', 'baz']
// Find elements using a predicate
const list = [{a: 1}, {a: 2}, {a: 3}]
R.find(R.propEq('a', 2))(list) //=> {a: 2}
R.find(R.propEq('a', 4))(list) //=> undefined
// Flatten a list of list into a single list
const list = [1, 2, [3, 4], 5, [6, [7, 8, [9, [10, 11], 12]]]]
R.flatten(list) //=> [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]

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Logic functions
// Combine predicates into a single function
var gt10 = x => x > 10
var even = x => x % 2 === 0
var gt10even = R.both(gt10, even)
gt10even(100) //=> true
gt10even(101) //=> false
// Functional switch case (aka. pattern matching?)
var whatHappensAtTemperature = R.cond([
[R.equals(0), R.always('water freezes at 0°C')],
[R.equals(100), R.always('water boils at 100°C')],
[R.T, temp => 'nothing special happens at ' + temp + '°C']
])
whatHappensAtTemperature(0) //=> 'water freezes at 0°C'
whatHappensAtTemperature(50) //=> 'nothing special happens at 50°C'
whatHappensAtTemperature(100) //=> 'water boils at 100°C'

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Object functions
// Add a key and value to an already existing object
R.assoc('c', 3, {a: 1, b: 2}) //=> {a: 1, b: 2, c: 3}
// Remove a key from an already existing object
R.dissoc('b', {a: 1, b: 2, c: 3}) //=> {a: 1, c: 3}
// Do the same with a nested path
R.assocPath(['a', 'b', 'c'], 42, {a: {b: {c: 0}}})
//=> {a: {b: {c: 42}}}
// Check if an object contains a key
var hasName = R.has('name')
hasName({name: 'alice'}) //=> true
hasName({name: 'bob'}) //=> true
hasName({}) //=> false
// Pick some properties from objects
var abby = {name: 'Abby', age: 7, hair: 'blond', grade: 2}
var fred = {name: 'Fred', age: 12, hair: 'brown', grade: 7}
R.project(['name', 'grade'], [abby, fred])
//=> [{name: 'Abby', grade: 2}, {name: 'Fred', grade: 7}]

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Relation functions
// Lots of comparison functions
// Kinda tricky, but also kinda natural
R.gt(2, 1) // 2 > 1
R.gt(2, 2) // 2 > 2
R.gte(2, 2) // 2 >= 2
R.gte(3, 2) // 3 >= 2
R.lt(2, 1) // 2 < 1
R.lt(2, 2) // 2 < 2
R.lte(2, 2) // 2 <= 2
R.lte(3, 2) // 3 <= 2
// Restrict a number to a range
R.clamp(1, 10, -1) // => 1
R.clamp(1, 10, 11) // => 10
// Intersect two lists
R.intersection([1,2,3,4], [7,6,4,3]) //=> [4, 3]

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Ramda works well with Promise

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Ramda and Promises
app.get('/v1/plants/:id', auth.active, (req, res) => {
db.plants.find({ id: req.params.id })
.then(R.head)
.then(R.bind(res.send, res))
})

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Ramda and Promises
function timesValues (number) {
return spot(number)
.then(spot =>
db.collection('zone_type_values')
.findOne({ id: spot.zone_type_value_id })
.then(R.prop('time_values'))
.then(R.assoc('timesValues', R.__, spot))
.then(R.pickAll(['id', 'name', 'timesValues']))
)
}

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Thanks for watching
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