potentially

A maybe/option type implementation with separate derived types to reduce branching.

Install

npm install potentially

Usage

const { Maybe, None, Some } = require('potentially')

Some.of(1) // Some(1)
  .and(None.of()) // None
  .or(Maybe.of(2)) // Some(2)
  .map(v => v * 2) // Some(4)
  .filter(v => v === 2) // None
  .expect("Oh no! It's a None! :(") // throws because there is no value

API

Maybe.of([ value ])

If value is undefined this function will return a None instance, otherwise it will return a Some instance containing the value. If value is already a Maybe it will just return the value. It is recommended to use None.of(...) and Some.of(...) instead if you already know which type it should be.

Maybe.some(value)

Returns a Some instance containing the value.

Maybe.none()

Returns a None instance.

None.of()

Returns a None instance, ignoring any input value if provided.

Some.of(value)

Returns a Some instance containing the value.

maybe.isSome

None: Returns false. Some: Returns true.

maybe.isNone

None: Returns true. Some: Returns false.

maybe.value

None: Throws an error with a 'Maybe is empty' message. Some: Returns the contained value.

maybe.expect(message)

None: Throws an error with the given message. Some: Returns the contained value.

maybe.map(func)

None: Returns this and skips the func as None types should remain None types. Some: Returns a Maybe of the result of calling func with the contained value. Can also return Maybe types from func to determine type explicitly rather than relying on internal type checking of Maybe, this allows a Some to contain undefined.

maybe.filter(func)

None: Returns this and skips the func as None types should remain None types. Some: Calls func on the contained value and return None if false or this if true.

maybe.and(other)

None: Returns this because it fails the left-hand condition of the and check and should remain None. Some: Returns other because it passes the left-hand condition.

None.or(other)

None: Returns other because it fails the left-hand condition of the or check. Some: Returns this because it passes the left-hand condition.

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Copyright (c) 2019 Stephen Belanger

Licensed under MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.