# sanctuary-maybe > Fantasy Land -compliant Maybe type Latest version **2.1.0** (published 2020-01-19) · MIT license · 0 weekly downloads ## Install ```sh npm install sanctuary-maybe pnpm add sanctuary-maybe yarn add sanctuary-maybe bun add sanctuary-maybe ``` ## Health **Score 15/100 (F)** — status: abandoned. Positive: no vulnerabilities. Warnings: low downloads; no types; no esm support. Negative: abandoned; low maintenance score. ## Facts | | | |---|---| | Version | 2.1.0 | | Published | 2020-01-19 | | First published | 2018-05-27 | | Weekly downloads | 0 | | License | MIT | | TypeScript types | none | | Module format | CommonJS | | Dependencies | 2 | | Unpacked size | 28.3 KB | | Known vulnerabilities | 0 | | Install scripts | no | | GitHub stars | 100 | | Maintainers | davidchambers | ## Links - npm: https://www.npmjs.com/package/sanctuary-maybe - Repository: https://github.com/sanctuary-js/sanctuary-maybe - Homepage: https://github.com/sanctuary-js/sanctuary-maybe#readme - Issues: https://github.com/sanctuary-js/sanctuary-maybe/issues - npm.io page: https://npm.io/package/sanctuary-maybe ## Dependencies (2) - [sanctuary-show](https://npm.io/package/sanctuary-show.md) 2.0.0 - [sanctuary-type-classes](https://npm.io/package/sanctuary-type-classes.md) 12.1.0 ## Recent versions - 2.1.0 (latest) — 2020-01-19 - 2.0.0 — 2019-11-03 - 1.2.0 — 2019-04-27 - 1.1.0 — 2019-02-21 - 1.0.0 — 2018-05-27 ## README Fantasy Land # 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 ❌ ' ] ``` #### `Maybe :: TypeRep Maybe` Maybe [type representative][]. #### `Maybe.Nothing :: Maybe a` The empty value of type `Maybe a`. ```javascript > Nothing Nothing ``` #### `Maybe.Just :: a -⁠> Maybe a` Constructs a value of type `Maybe a` from a value of type `a`. ```javascript > Just (42) Just (42) ``` #### `Maybe.fantasy-land/empty :: () -⁠> Maybe a` - `empty (Maybe)` is equivalent to `Nothing` ```javascript > S.empty (Maybe) Nothing ``` #### `Maybe.fantasy-land/of :: a -⁠> Maybe a` - `of (Maybe) (x)` is equivalent to `Just (x)` ```javascript > S.of (Maybe) (42) Just (42) ``` #### `Maybe.fantasy-land/chainRec :: ((a -⁠> c, b -⁠> c, a) -⁠> Maybe c, a) -⁠> Maybe b` ```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) ``` #### `Maybe.fantasy-land/zero :: () -⁠> Maybe a` - `zero (Maybe)` is equivalent to `Nothing` ```javascript > S.zero (Maybe) Nothing ``` #### `Maybe#@@show :: Showable a => Maybe a ~> () -⁠> String` - `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"])' ``` #### `Maybe#fantasy-land/equals :: Setoid a => Maybe a ~> Maybe a -⁠> Boolean` - `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 ``` #### `Maybe#fantasy-land/lte :: Ord a => Maybe a ~> Maybe a -⁠> Boolean` - `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)] ``` #### `Maybe#fantasy-land/concat :: Semigroup a => Maybe a ~> Maybe a -⁠> Maybe 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]) ``` #### `Maybe#fantasy-land/filter :: Maybe a ~> (a -⁠> Boolean) -⁠> Maybe 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) ``` #### `Maybe#fantasy-land/map :: Maybe a ~> (a -⁠> b) -⁠> Maybe b` - `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) ``` #### `Maybe#fantasy-land/ap :: Maybe a ~> Maybe (a -⁠> b) -⁠> Maybe b` - `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) ``` #### `Maybe#fantasy-land/chain :: Maybe a ~> (a -⁠> Maybe b) -⁠> Maybe b` - `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') ``` #### `Maybe#fantasy-land/alt :: Maybe a ~> Maybe a -⁠> Maybe 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) ``` #### `Maybe#fantasy-land/reduce :: Maybe a ~> ((b, a) -⁠> b, b) -⁠> b` - `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' ``` #### `Maybe#fantasy-land/traverse :: Applicative f => Maybe a ~> (TypeRep f, a -⁠> f b) -⁠> f (Maybe b)` - `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')] ``` #### `Maybe#fantasy-land/extend :: Maybe a ~> (Maybe a -⁠> b) -⁠> Maybe b` - `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 --- _Source: https://npm.io/package/sanctuary-maybe · Machine-readable twin of the npm.io package page. 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