Maybe

The Maybe monad is, like the Either monad, a union type. It contextually evaluates to one of either a Just or Nothing value. The former is transformable while the latter always yields a unit type - null. To follow is a list of functions that meld well with the Maybe type.

maybe

maybe(default, function, maybe)

maybe :: b -> (a -> b) -> Maybe a -> b

Performs case-analysis on the Maybe monad: applies function to value inside Just if Maybe value is not Nothing, and returns a default value otherwise.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• default - Arbitrary default value
• function - Aribitrary function to apply to instance of Just
• maybe - Instance of Maybe monad

JavaScript

import { maybe, fromValue } from 'bingo-functional-js'
const val = 10const result = maybe(  val,  (x) => x ** 2,  fromValue(val).filter((x) => x % 2 == 0),)

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$val    = 10;$result = Maybe\maybe(  $val,  fn (int $x): int => $x ** 2,  Maybe::fromValue($val)->filter(fn (int $x): bool => $x % 2 == 0));

isJust & isNothing

isJust|isNothing(maybe)

isJust :: Maybe a -> Bool | isNothing :: Maybe a -> Bool

Returns true if the argument is of type Just|Nothing.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• maybe - Instance of Maybe monad

JavaScript

import { isJust, isNothing, fromValue } from 'bingo-functional-js'
const just = fromValue(2)const nothing = fromValue(null)
isJust(nothing)isNothing(just)

PHP

use function Chemem\Bingo\Functional\Functors\Monads\Maybe;
$just     = Maybe::fromValue(2);$nothing  = Maybe::nothing();
echo Maybe\isJust($nothing);echo Maybe\isNothing($just);

fromJust

fromJust(maybe)

fromJust :: Maybe a -> a

Extracts the element out of a Just and throws an error if its argument is Nothing.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• maybe - Instance of Maybe monad

JavaScript

import { fromJust, fromValue } from 'bingo-functional-js'
const result = fromJust(fromValue('foo'))

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$result = Maybe\fromJust(Maybe::fromValue('foo'));

fromMaybe

fromMaybe(default, maybe)

fromMaybe :: a -> Maybe a -> a

Returns default value if Maybe is Nothing; returns Just value otherwise.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• default - Arbitrary default value
• maybe - Instance of Maybe monad

JavaScript

import { fromMaybe } from 'bingo-functional-js'
const result = fromMaybe(0, fromValue(null))

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$result = Maybe\fromMaybe(Maybe::nothing());

listToMaybe

listToMaybe(list)

listToMaybe :: [a] -> Maybe a

Returns Nothing if the primary argument is an empty list or a Just instance containing the first element of a non-empty list.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• list - An arbitrary array

JavaScript

import { listToMaybe } from 'bingo-functional-js'
const result = listToMaybe([3, 4, 5, 6, 7])

PHP

use function Chemem\Bingo\Functional\Functors\Monads\Maybe;
$result = Maybe\listToMaybe(range(3, 7));

maybeToList

maybeToList(maybe)

maybeToList :: Maybe a -> [a]

Returns an empty list when given Nothing or a singleton list otherwise.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• maybe - Instance of Maybe monad

JavaScript

import { maybeToList, fromValue } from 'bingo-functional-js'
const list = maybeToList(fromValue('foo'))

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$list = Maybe\maybeToList(Maybe::just('foo'));

catMaybes

catMaybes(maybes)

catMaybes :: [Maybe a] -> [a]

Returns a list of all the Just values from a list of Maybe objects.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• maybes - List of Maybe objects

JavaScript

import { catMaybes, fromValue } from 'bingo-functional-js'
const maybes = catMaybes([fromValue('foo'), fromValue(null), fromValue(12)])

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$maybes = Maybe\catMaybes([  Maybe::just('foo'),  Maybe::nothing(),  Maybe::just(12)]);

mapMaybe

mapMaybe(function, list)

mapMaybe :: (a -> Maybe b) -> [a] -> [b]

The mapMaybe function is a version of map which can throw out elements.

Since:

• bingo-functional - v1.11.0
• bingo-functional-js - v0.1.0

Argument(s):

• function - A discretionary transformer function
• list - An arbitrary list

JavaScript

import { mapMaybe, concat, fromValue } from 'bingo-functional-js'
const res = mapMaybe(  (x) => fromValue(concat('', x, 'ing')),  ['eat', 'sleep', 'fish', 'mix'],)

PHP

use Chemem\Bingo\Functional\Functors\Monads\Maybe;
$res = Maybe\mapMaybe(  fn (string $x) => Maybe::right(f\concat('', $x, 'ing')),  ['eat', 'sleep', 'fish', 'mix']);