flow-static-land

Features

• statically type checked by Flow
• PureScript-like standard library
• static land compatible

The idea (faking higher kinded types in Flow) is based on the paper Lightweight higher-kinded polymorphism and elm-brands.

• Semigroup
• Monoid
• Functor
• Applicative
• Monad
• Foldable
• Traversable
• ChainRec
• Alternative
• Eff
• Arr
• Maybe
• Either
• Task
• State
• Writer
• Reader

and many more...

Example

import * as maybe from 'flow-static-land/lib/Maybe'
import * as arr from 'flow-static-land/lib/Arr'

const f = (n) => n * 2
const g = (n) => n + 1

// functor
maybe.map(f, maybe.Nothing) // => null
maybe.map(f, maybe.of(3)) // => 6

const a1 = arr.inj([f, g])
const a2 = arr.inj([1, 2, 3])

// applicative
arr.ap(a1, a2) // => [2, 4, 6, 2, 3, 4]

Statically type checked

maybe.map(f, maybe.of('s'))

Error

maybe.map(f, maybe.of('s'))
                  ^^^^^^^^^^^^^ call of method `of`
const f = (n) => n * 2
                 ^ string. This type is incompatible with
const f = (n) => n * 2
                 ^^^^^ number

Related blog posts

• Higher kinded types with Flow
• Expressing side effects with the Eff monad
• Phantom types with Flow

More examples

examples directory:

• a Signal library (purescript-signal porting)
• a QuickCheck library (purescript-quickcheck partial porting)

Setup

npm install flow-static-land --save

Babel config

{
  "presets": ["es2015"],
  "plugins" : [
    "syntax-flow",
    "transform-flow-strip-types",
    "transform-class-properties"
  ]
}

License

The MIT License (MIT)