Maybe (Monad) ​

The Maybe type in PureEval may differ from the Data Maybe found in other functional languages like Haskell. In PureEval, Maybe is a fusion of Data Maybe and Class Monad.

Maybe ​

The Maybe type encapsulates a value that may be indeterminate.

If an operation on a specific value within Maybe fails, it turns into Nothing.

Both undefined and null are considered as Nothing.

• Type

Maybe.of() ​

Lifts a value into a Maybe type.

• Type

• Example

Maybe.of(1); // Just 1
Maybe.of(null); // Nothing

Maybe.of(1); // Just 1
Maybe.of(null); // Nothing

Maybe.is() ​

Determines whether a value is of type Maybe.

• Type

• Example

Maybe.is(Just(1)); // true
Maybe.is(Nothing); // true

Maybe.is(Just(1)); // true
Maybe.is(Nothing); // true

Maybe.isNothing() ​

Determines if the Maybe is Nothing.

• Type

• Example

Just(1).isNothing(); // false
Just(null).isNothing(); // true

Just(1).isNothing(); // false
Just(null).isNothing(); // true

Maybe.map() ​

Maps the value inside Maybe through a function, constructing a new Maybe to hold the result.

• Type

• Example

Just(1).map(add(114513)); // Just 114514

Just(1).map(add(114513)); // Just 114514

Maybe.fold() ​

Applies a function to the value within Maybe a.

Takes two unary function parameters for handling cases when Maybe a is Nothing and when it is not.

• Type

• Example

Just('The body next door').fold(() => 'Nothing', id); // "The body next door"

Just('The body next door').fold(() => 'Nothing', id); // "The body next door"

Maybe.chain() ​

Chains a function that returns a Maybe type, allowing for method chaining.

• Type

• Example

// Example demonstrating method chaining using Maybe
// [...]
console.log(city); // 'Anytown'

// Example demonstrating method chaining using Maybe
// [...]
console.log(city); // 'Anytown'

Just() ​

Constructor function for the Maybe type.

Equivalent to Maybe.of.

• Type

• Example

Just(1); // Just 1

Just(1); // Just 1

Nothing ​

Constructor for the Maybe type representing the absence of a value.