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sanctuary-maybe

(★ 100)

:rainbow: Fantasy Land -compliant Maybe type

파일 탐색기

최종 버전 다운로드 (.zip)

- config.yml
- CONTRIBUTING.md
- FUNDING.yml
- index.js
- package.json
.config
.eslintrc.json
.gitignore
.npmrc
index.js
LICENSE
package.json
README.md

# 설치 가이드

1. 코드 내려받기

git clone https://github.com/sanctuary-js/sanctuary-maybe

깃허브에서 프로젝트 코드 전체를 내 컴퓨터로 내려받습니다.

cd sanctuary-maybe

방금 내려받은 프로젝트 폴더 안으로 이동합니다.

2. Node.js

쉬움 추천

사전 준비물

Git GitHub에서 프로젝트 코드를 내려받으려면 필요합니다.
Node.js npm 명령어를 쓰려면 Node.js가 설치되어 있어야 합니다. LTS(장기지원) 버전을 추천합니다.

npm install

package.json에 명시된 라이브러리들을 내려받아 설치합니다.

npm start

개발/실행 서버를 켭니다.

✅ 명령어 실행 후 터미널에 나타나는 주소(보통 http://localhost:3000 형태)를 브라우저에서 열어보세요.

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<a href="https://github.com/fantasyland/fantasy-land"><img alt="Fantasy Land" src="https://raw.githubusercontent.com/fantasyland/fantasy-land/master/logo.png" width="75" height="75" align="left"></a>

# sanctuary-maybe

The Maybe type represents optional values: a value of type `Maybe a` is
either Nothing (the empty value) or a Just whose value is of type `a`.

`Maybe a` satisfies the following [Fantasy Land][] specifications:

```javascript
> const Useless = require ('sanctuary-useless')

> const isTypeClass = x =>
.   type (x) === 'sanctuary-type-classes/TypeClass@1'

> S.map (k => k + ' '.repeat (16 - k.length) +
.             (Z[k].test (Just (Useless)) ? '\u2705   ' :
.              Z[k].test (Nothing)        ? '\u2705 * ' :
.              /* otherwise */              '\u274C   '))
.       (S.keys (S.unchecked.filter (isTypeClass) (Z)))
[ 'Setoid          ✅ * ',  // if ‘a’ satisfies Setoid
. 'Ord             ✅ * ',  // if ‘a’ satisfies Ord
. 'Semigroupoid    ❌   ',
. 'Category        ❌   ',
. 'Semigroup       ✅ * ',  // if ‘a’ satisfies Semigroup
. 'Monoid          ✅ * ',  // if ‘a’ satisfies Semigroup
. 'Group           ❌   ',
. 'Filterable      ✅   ',
. 'Functor         ✅   ',
. 'Bifunctor       ❌   ',
. 'Profunctor      ❌   ',
. 'Apply           ✅   ',
. 'Applicative     ✅   ',
. 'Chain           ✅   ',
. 'ChainRec        ✅   ',
. 'Monad           ✅   ',
. 'Alt             ✅   ',
. 'Plus            ✅   ',
. 'Alternative     ✅   ',
. 'Foldable        ✅   ',
. 'Traversable     ✅   ',
. 'Extend          ✅   ',
. 'Comonad         ❌   ',
. 'Contravariant   ❌   ' ]
```

#### <a name="Maybe" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L147">`Maybe :: TypeRep Maybe`</a>

Maybe [type representative][].

#### <a name="Maybe.Nothing" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L151">`Maybe.Nothing :: Maybe a`</a>

The empty value of type `Maybe a`.

```javascript
> Nothing
Nothing
```

#### <a name="Maybe.Just" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L161">`Maybe.Just :: a -⁠> Maybe a`</a>

Constructs a value of type `Maybe a` from a value of type `a`.

```javascript
> Just (42)
Just (42)
```

#### <a name="Maybe.fantasy-land/empty" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L184">`Maybe.fantasy-land/empty :: () -⁠> Maybe a`</a>

- `empty (Maybe)` is equivalent to `Nothing`

```javascript
> S.empty (Maybe)
Nothing
```

#### <a name="Maybe.fantasy-land/of" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L194">`Maybe.fantasy-land/of :: a -⁠> Maybe a`</a>

- `of (Maybe) (x)` is equivalent to `Just (x)`

```javascript
> S.of (Maybe) (42)
Just (42)
```

#### <a name="Maybe.fantasy-land/chainRec" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L207">`Maybe.fantasy-land/chainRec :: ((a -⁠> c, b -⁠> c, a) -⁠> Maybe c, a) -⁠> Maybe b`</a>

```javascript
> Z.chainRec (
.   Maybe,
.   (next, done, x) =>
.     x <= 1 ? Nothing : Just (x >= 1000 ? done (x) : next (x * x)),
.   1
. )
Nothing

> Z.chainRec (
.   Maybe,
.   (next, done, x) =>
.     x <= 1 ? Nothing : Just (x >= 1000 ? done (x) : next (x * x)),
.   2
. )
Just (65536)
```

#### <a name="Maybe.fantasy-land/zero" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L236">`Maybe.fantasy-land/zero :: () -⁠> Maybe a`</a>

- `zero (Maybe)` is equivalent to `Nothing`

```javascript
> S.zero (Maybe)
Nothing
```

#### <a name="Maybe.prototype.@@show" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L246">`Maybe#@@show :: Showable a => Maybe a ~> () -⁠> String`</a>

- `show (Nothing)` is equivalent to `'Nothing'`
  - `show (Just (x))` is equivalent to `'Just (' + show (x) + ')'`

```javascript
> show (Nothing)
'Nothing'

> show (Just (['foo', 'bar', 'baz']))
'Just (["foo", "bar", "baz"])'
```

#### <a name="Maybe.prototype.fantasy-land/equals" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L265">`Maybe#fantasy-land/equals :: Setoid a => Maybe a ~> Maybe a -⁠> Boolean`</a>

- `Nothing` is equal to `Nothing`
  - `Just (x)` is equal to `Just (y)` [iff][] `x` is equal to `y`
    according to [`Z.equals`][]
  - `Nothing` is never equal to `Just (x)`

```javascript
> S.equals (Nothing) (Nothing)
true

> S.equals (Just ([1, 2, 3])) (Just ([1, 2, 3]))
true

> S.equals (Just ([1, 2, 3])) (Just ([3, 2, 1]))
false

> S.equals (Just ([1, 2, 3])) (Nothing)
false
```

#### <a name="Maybe.prototype.fantasy-land/lte" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L292">`Maybe#fantasy-land/lte :: Ord a => Maybe a ~> Maybe a -⁠> Boolean`</a>

- `Nothing` is (less than or) equal to `Nothing`
  - `Just (x)` is less than or equal to `Just (y)` [iff][] `x` is less
    than or equal to `y` according to [`Z.lte`][]
  - `Nothing` is always less than `Just (x)`

```javascript
> S.filter (S.lte (Nothing)) ([Nothing, Just (0), Just (1), Just (2)])
[Nothing]

> S.filter (S.lte (Just (1))) ([Nothing, Just (0), Just (1), Just (2)])
[Nothing, Just (0), Just (1)]
```

#### <a name="Maybe.prototype.fantasy-land/concat" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L313">`Maybe#fantasy-land/concat :: Semigroup a => Maybe a ~> Maybe a -⁠> Maybe a`</a>

- `concat (Nothing) (Nothing)` is equivalent to `Nothing`
  - `concat (Just (x)) (Just (y))` is equivalent to
    `Just (concat (x) (y))`
  - `concat (Nothing) (Just (x))` is equivalent to `Just (x)`
  - `concat (Just (x)) (Nothing)` is equivalent to `Just (x)`

```javascript
> S.concat (Nothing) (Nothing)
Nothing

> S.concat (Just ([1, 2, 3])) (Just ([4, 5, 6]))
Just ([1, 2, 3, 4, 5, 6])

> S.concat (Nothing) (Just ([1, 2, 3]))
Just ([1, 2, 3])

> S.concat (Just ([1, 2, 3])) (Nothing)
Just ([1, 2, 3])
```

#### <a name="Maybe.prototype.fantasy-land/filter" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L341">`Maybe#fantasy-land/filter :: Maybe a ~> (a -⁠> Boolean) -⁠> Maybe a`</a>

- `filter (p) (Nothing)` is equivalent to `Nothing`
  - `filter (p) (Just (x))` is equivalent to `p (x) ? Just (x) : Nothing`

```javascript
> S.filter (isFinite) (Nothing)
Nothing

> S.filter (isFinite) (Just (Infinity))
Nothing

> S.filter (isFinite) (Just (Number.MAX_SAFE_INTEGER))
Just (9007199254740991)
```

#### <a name="Maybe.prototype.fantasy-land/map" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L363">`Maybe#fantasy-land/map :: Maybe a ~> (a -⁠> b) -⁠> Maybe b`</a>

- `map (f) (Nothing)` is equivalent to `Nothing`
  - `map (f) (Just (x))` is equivalent to `Just (f (x))`

```javascript
> S.map (Math.sqrt) (Nothing)
Nothing

> S.map (Math.sqrt) (Just (9))
Just (3)
```

#### <a name="Maybe.prototype.fantasy-land/ap" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L382">`Maybe#fantasy-land/ap :: Maybe a ~> Maybe (a -⁠> b) -⁠> Maybe b`</a>

- `ap (Nothing) (Nothing)` is equivalent to `Nothing`
  - `ap (Nothing) (Just (x))` is equivalent to `Nothing`
  - `ap (Just (f)) (Nothing)` is equivalent to `Nothing`
  - `ap (Just (f)) (Just (x))` is equivalent to `Just (f (x))`

```javascript
> S.ap (Nothing) (Nothing)
Nothing

> S.ap (Nothing) (Just (9))
Nothing

> S.ap (Just (Math.sqrt)) (Nothing)
Nothing

> S.ap (Just (Math.sqrt)) (Just (9))
Just (3)
```

#### <a name="Maybe.prototype.fantasy-land/chain" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L409">`Maybe#fantasy-land/chain :: Maybe a ~> (a -⁠> Maybe b) -⁠> Maybe b`</a>

- `chain (f) (Nothing)` is equivalent to `Nothing`
  - `chain (f) (Just (x))` is equivalent to `f (x)`

```javascript
> const head = xs => xs.length === 0 ? Nothing : Just (xs[0])

> S.chain (head) (Nothing)
Nothing

> S.chain (head) (Just ([]))
Nothing

> S.chain (head) (Just (['foo', 'bar', 'baz']))
Just ('foo')
```

#### <a name="Maybe.prototype.fantasy-land/alt" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L433">`Maybe#fantasy-land/alt :: Maybe a ~> Maybe a -⁠> Maybe a`</a>

- `alt (Nothing) (Nothing)` is equivalent to `Nothing`
  - `alt (Just (x)) (Nothing)` is equivalent to `Just (x)`
  - `alt (Nothing) (Just (x))` is equivalent to `Just (x)`
  - `alt (Just (y)) (Just (x))` is equivalent to `Just (x)`

```javascript
> S.alt (Nothing) (Nothing)
Nothing

> S.alt (Just (1)) (Nothing)
Just (1)

> S.alt (Nothing) (Just (2))
Just (2)

> S.alt (Just (4)) (Just (3))
Just (3)
```

#### <a name="Maybe.prototype.fantasy-land/reduce" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L460">`Maybe#fantasy-land/reduce :: Maybe a ~> ((b, a) -⁠> b, b) -⁠> b`</a>

- `reduce (f) (x) (Nothing)` is equivalent to `x`
  - `reduce (f) (x) (Just (y))` is equivalent to `f (x) (y)`

```javascript
> S.reduce (S.concat) ('abc') (Nothing)
'abc'

> S.reduce (S.concat) ('abc') (Just ('xyz'))
'abcxyz'
```

#### <a name="Maybe.prototype.fantasy-land/traverse" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L479">`Maybe#fantasy-land/traverse :: Applicative f => Maybe a ~> (TypeRep f, a -⁠> f b) -⁠> f (Maybe b)`</a>

- `traverse (A) (f) (Nothing)` is equivalent to `of (A) (Nothing)`
  - `traverse (A) (f) (Just (x))` is equivalent to `map (Just) (f (x))`

```javascript
> S.traverse (Array) (S.words) (Nothing)
[Nothing]

> S.traverse (Array) (S.words) (Just ('foo bar baz'))
[Just ('foo'), Just ('bar'), Just ('baz')]
```

#### <a name="Maybe.prototype.fantasy-land/extend" href="https://github.com/sanctuary-js/sanctuary-maybe/blob/v2.1.0/index.js#L498">`Maybe#fantasy-land/extend :: Maybe a ~> (Maybe a -⁠> b) -⁠> Maybe b`</a>

- `extend (f) (Nothing)` is equivalent to `Nothing`
  - `extend (f) (Just (x))` is equivalent to `Just (f (Just (x)))`

```javascript
> S.extend (S.reduce (S.add) (1)) (Nothing)
Nothing

> S.extend (S.reduce (S.add) (1)) (Just (99))
Just (100)
```

[Fantasy Land]:             https://github.com/fantasyland/fantasy-land/tree/v4.0.1
[`Z.equals`]:               https://github.com/sanctuary-js/sanctuary-type-classes/tree/v12.1.0#equals
[`Z.lte`]:                  https://github.com/sanctuary-js/sanctuary-type-classes/tree/v12.1.0#lte
[iff]:                      https://en.wikipedia.org/wiki/If_and_only_if
[type representative]:      https://github.com/fantasyland/fantasy-land/tree/v4.0.1#type-representatives