https://github.com/risto-stevcev/do-notation

:arrow_left: Do notation for Fantasy Land monad types
https://github.com/risto-stevcev/do-notation

do do-notation fantasy-land monad notation sugar

Last synced: 19 days ago
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:arrow_left: Do notation for Fantasy Land monad types

• Host: GitHub
• URL: https://github.com/risto-stevcev/do-notation
• Owner: Risto-Stevcev
• License: mit
• Created: 2016-03-02T02:15:28.000Z (about 9 years ago)
• Default Branch: master
• Last Pushed: 2016-04-18T13:36:47.000Z (about 9 years ago)
• Last Synced: 2024-10-31T03:52:03.072Z (7 months ago)
• Topics: do, do-notation, fantasy-land, monad, notation, sugar
• Language: JavaScript
• Homepage: https://www.npmjs.com/package/do-notation
• Size: 6.84 KB
• Stars: 12
• Watchers: 4
• Forks: 0
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        
# Do Notation

[![Build Status](https://travis-ci.org/Risto-Stevcev/do-notation.svg)](https://travis-ci.org/Risto-Stevcev/do-notation)

[![Coverage Status](https://coveralls.io/repos/github/Risto-Stevcev/do-notation/badge.svg?branch=master)](https://coveralls.io/github/Risto-Stevcev/do-notation?branch=master)

Do notation for Fantasy Land monad types.

[![Fantasy Land](https://github.com/fantasyland/fantasy-land/raw/master/logo.png)](https://github.com/fantasyland/fantasy-land/)

## Examples

It uses `yield` to "unbox" the Monad (the `<-` in Haskell), which can then be transformed and fed to the next Monad in the `Do` block. The `Do` function returns the last Monad in the `Do` block:

```js

const Do = require('do-notation')

let maybeString = Do(function*() {

  let foo = yield S.Maybe.of('foo')

  console.log(foo)

  // 'foo'

  let bar = yield S.Maybe.of('bar' + foo)

  console.log(bar)

  // 'barfoo'

  let baz = yield S.Maybe.of('baz' + bar)

  console.log(baz)

  // 'bazbarfoo'

}).toString()

console.log(maybeString)

// 'Just("bazbarfoo")'

```

## Implementation

The entire implementation is very succinct and simple:

```js

Do = function(generatorFunction) {

  const generator = generatorFunction()

  return function next(error, v) {

    const res = generator.next(v)

    if (res.done)

      return res.value

    else

      return res.value.chain((v) => next(null, v) || res.value.of(v))

  }()

}

module.exports = { Do: Do }

```