exalted.future

exalted.future

Experimental

A javascript and typescript monadic library & functional fun. fantasy-land compliant, mostly.

The style of monad object is inspired by DrBoolean course on egghead.io.

The choice for cata, encase, head, tail, last is inspired by rametta's take on monads in pratica.

This is, in many ways, an evolution of oncha which I wrote with other people many years ago and is no longer maintained.

Install

yarn add exalted.future

Types

Name	Apply	Applicative	Setoid	Foldable	Functor	Monad	Chain
Either	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎
Future	✔︎	—	✔︎	✔︎	✔︎	—	✔︎
Identity	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎
Maybe	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎	✔︎

• There is a divergence from fantasy-land where reduce is named cata and loosely based on daggy's union types.
• fold always folds on identity a => a, except when it does not like with the Future.
• Maybe.map will return Nothing if the callback function returns null. In other words Just(null) is impossible, unless you call the 'static' constructor like this Just.of(null). See this pr for some explanation.
• Left is not 100% applicative.

All

These functions are available on all types.

ap

Apply

chain :: (a -> b) -> b

Id(5).chain(a => Id(a))
//=> Id(5)

// You can use chain to join the monads.
Id(Id(5)).chain(a => a)
//=> Id(5)

equals

Setoid

equals :: Id -> Boolean

Id(1).equals(Id(1))
//=> true

Id(2).equals(Id(1))
//=> false

Id(2).equals(Id(1)) === Id(1).equals(Id(1))
//=> false

chain

Chain

chain :: (a -> b) -> b

Id(5).chain(a => Id(a))
//=> Id(5)

// You can use chain to join the monads.
Id(Id(5)).chain(a => a)
//=> Id(5)

map

Functor

map :: (a -> b) -> Id of b

Id(7).map(a => a * 2)
//=> Id(14)

of

Applicative

of :: a -> Id of a

Id(5).of(6)
//=> Id(6)

Id(5).of(Id(6))
//=> Id(Id(6))

fold

Foldable

fold :: (a -> b) -> b

Id(5).fold()
//=> 5

Id(5).fold()
//=> 6

cata

Foldable

cata :: ({ Left: () -> b, Right -> a -> a }) -> a | b

Id(5).cata({
    Right: a => a
  })
//=> 5

Id(5).cata({
    Right: a => a + 1
  })
//=> 6

Right(5).cata({
    Left: a => 8 // ignored 
    Right: a => a + 1
  })
//=> 6

Left(5).cata({
    Left: a => a + 1 
    Right: a => 8 // ignored
  })
//=> 6

inspect

inspect :: () -> String

Id(5).inspect()
//=> Id(5)

Id

Identity monad.

Id(5)
  .map(num => num * 7)
  .map(num => num - 1)
  .cata({
    Right: a => a
  })
//=> 34

Maybe

Maybe monad.

// Maybe of a string
Maybe('Hello exalted one')
  .map(sentence => sentence.toUpperString())
  .map(sentence => `${sentence}!`)
  .cata({
    Right: console.log
  })
//=> 'HELLO EXALTED ONE!'

// Maybe of nothing
Maybe(null)
  .map(sentence => sentence.toUpperString())
  .alt(() => 'Maybe received a null')
  .cata({
    Right: console.log
  })
//=> 'Maybe received a null'

alt

Sets the value to cata on.

alt :: Any -> Nothing of Any

Maybe(1).alt(5).cata({
    Right: a => a
  })
//=> 1

Maybe(null).alt(5).cata({
    Right: a => a
  })
//=> 5

cata

Foldable

cata :: ({ Left: () -> b, Right: a -> b }) -> a|b

Maybe(5).cata({
    Right: a => a
  })
//=> 5

Maybe(5).cata({
    Left: () => { } // not called
    Right: a => a + 1
  })
//=> 6

Maybe(null).cata({
    Left: () => 'there was a null'
    Right: a => a + 1 // not called
  })
//=> there was a null

Either

An Either monad and nullable, Left, Right.

nullable('Hello') // this will return a Right('Hello')
  .cata({
    Left: () => 'Oops',
    Right: val => `${val} world!`
  })
//=> 'Hello world!'

nullable(null) // this will return a Left()
  .cata({
    Left: () => 'Oops',
    Right: val => `${val} world!`
  })
//=> 'Oops'

const extractEmail = obj => obj.email ? Right(obj.email) : Left()
extractEmail({ email: '[e-mail]' }
  .map(extractDomain)
  .cata({
    Left: () => 'No email found!',
    Right:x => x
  })
//=> 'example.com'

extractEmail({ name: 'user' }
  .map(extractDomain) // this will not get executed
  .cata({
    Left: () => 'No email found!',
    Right: x => x
  })
//=> 'No email found!'

cata

Foldable - Folds foldable object.

cata :: ({ Left: () -> b, Right -> a -> a }) -> a | b

Right(5).cata({
    Left: () => 1,
    Right: a => a + 2
  })
//=> 7

Left(5).cata(a => a + 1)
//=> 6

Future

A Future monad for async computation.

// Basic usage
Future((reject, resolve) => resolve('Yay'))
  .map(res => res.toUpperString())
  .fork(
    err => log(`Err: ${err}`),
    res => log(`Res: ${res}`))
//=> 'YAY'

// Handle promises
Future.promise(fetch('https://api.awesome.com/catOfTheDay'))
  .fork(
    err => log('There was an error fetching the cat of the day :('),
    cat => log('Cat of the day: ' + cat))
//=> 'Cat of the day: Garfield'

// Chain http calls
Future.promise(fetch('https://api.awesome.com/catOfTheDay'))
  .chain(cat => Future.promise(fetch(`https://api.catfacts.com/${cat}`)))
  .fork(
    err => log('There was an error fetching the cat of the day :('),
    facts => log('Facts for cat of the day: ' + facts))
//=> 'Facts for cat of the day: Garfield is awesome.'

all

Forks all the futures.

all :: ([Futures]) -> b

Future.all(
  Future.of('apple'),
  Future((left, right) => setTimeout(() => right('orange'), 1000)),
  Future.of('lemon')
).fork(
  () => (),
  ([ apple, orange, lemon ]) =>
    //=> apple, orange, lemon
)

fold

Foldable Folds on identity.

fold :: (a -> b) -> b

Future.of(5).fold()
//=> 5

fork

Executes the Future returning a Future of the resuts.

fork :: (a -> a, b -> b) -> Future of a | b

Future((left, right) => right(5)).fork(a => a, a => a)
//=> Future of 5

Future((left, right) => left(Error('this is an error'))).fork(a => a)
//=> Future of Error

Higher Order Utilities

compose

Compose takes n functions as arguments and return a function.

const transform = compose(sentence => sentence.toUpperString(), sentence => `${sentence}!`)
const logTransform = compose(log, transform)

logTransform('Hello exalted one')
//=> 'HELLO EXALTED ONE!'

// supports miltiple arguments
compose(path.normalize, path.join)('./exalted', '/one')
//=> './exalted/one'

map

Map as partial application and first class with arity support.

map(a => a + 1, a => a * 3)([1, 2, 3])
//=> [4, 7, 10]

head, tail, last

Returns a Maybe.

head([1,2])
//=> Just(1)

head([])
//=> Nothing()

tail([1,2,3])
//=> Just([2,3])

tail([])
//=> Nothing()

last([1,2,3])
//=> Just(3)

last([])
//=> Nothing()

encase, encaseEither

Returns Left | Right.

encase(() => JSON.parse('["foo","bar","baz"]'))
//=> Just(['foo','bar','baz'])

encase(() => JSON.parse('['))
//=> Nothing()

encaseEither(() => JSON.parse('["foo","bar","baz"]'))
//=> Right(['foo','bar','baz'])

encaseEither(() => JSON.parse('['))
//=> Left(new SyntaxError ('Unexpected end of JSON input'))