Awesome
<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:
> 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
.
> 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
.
> 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 toNothing
> 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 toJust (x)
> 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>
> 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 toNothing
> 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) + ')'
> 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 toNothing
Just (x)
is equal toJust (y)
iffx
is equal toy
according toZ.equals
Nothing
is never equal toJust (x)
> 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 toNothing
Just (x)
is less than or equal toJust (y)
iffx
is less than or equal toy
according toZ.lte
Nothing
is always less thanJust (x)
> 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 toNothing
concat (Just (x)) (Just (y))
is equivalent toJust (concat (x) (y))
concat (Nothing) (Just (x))
is equivalent toJust (x)
concat (Just (x)) (Nothing)
is equivalent toJust (x)
> 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 toNothing
filter (p) (Just (x))
is equivalent top (x) ? Just (x) : Nothing
> 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 toNothing
map (f) (Just (x))
is equivalent toJust (f (x))
> 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 toNothing
ap (Nothing) (Just (x))
is equivalent toNothing
ap (Just (f)) (Nothing)
is equivalent toNothing
ap (Just (f)) (Just (x))
is equivalent toJust (f (x))
> 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 toNothing
chain (f) (Just (x))
is equivalent tof (x)
> 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 toNothing
alt (Just (x)) (Nothing)
is equivalent toJust (x)
alt (Nothing) (Just (x))
is equivalent toJust (x)
alt (Just (y)) (Just (x))
is equivalent toJust (x)
> 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 tox
reduce (f) (x) (Just (y))
is equivalent tof (x) (y)
> 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 toof (A) (Nothing)
traverse (A) (f) (Just (x))
is equivalent tomap (Just) (f (x))
> 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 toNothing
extend (f) (Just (x))
is equivalent toJust (f (Just (x)))
> S.extend (S.reduce (S.add) (1)) (Nothing)
Nothing
> S.extend (S.reduce (S.add) (1)) (Just (99))
Just (100)