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https://github.com/functionalland/functional

Common Functional Programming Algebraic data types for JavaScript that is compatible with most modern browsers and Deno.
https://github.com/functionalland/functional

algebraic-data-types browser catamorphism category-theory deno denoland either either-monad fold functional functional-programming functor io-monad maybe maybe-monad monoid task task-monad

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Common Functional Programming Algebraic data types for JavaScript that is compatible with most modern browsers and Deno.

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Functional



Common Functional Programming Algebraic data types for JavaScript that is compatible with most modern browsers and Deno.



[![deno land](http://img.shields.io/badge/available%20on-deno.land/x-lightgrey.svg?logo=deno&labelColor=black)](https://deno.land/x/[email protected])

[![deno version](https://img.shields.io/badge/deno-^1.6.1-lightgrey?logo=deno)](https://github.com/denoland/deno)

[![GitHub release](https://img.shields.io/github/v/release/sebastienfilion/functional)](https://github.com/sebastienfilion/functional/releases)

[![GitHub licence](https://img.shields.io/github/license/sebastienfilion/functional)](https://github.com/sebastienfilion/functional/blob/v1.3.4/LICENSE)

[![Discord Chat](https://img.shields.io/discord/790708610023555093.svg)](https://discord.gg/)



  * [Either](#either)

  * [IO](#io)

  * [Maybe](#maybe)

  * [Pair](#pair)

  * [Task](#task)

  * [Type factory](#type-factory)

  * [Sum Type factory](#sum-type-factory)

  * [Utilities](#utilities)

  * [TypeScript](#typescript)



## Usage



This example uses the [Ramda library](https://ramdajs.com) - for simplification - but you should be able to use any library that implements

the [Fantasy-land specifications](https://github.com/fantasyland/fantasy-land).



```js

import { compose, converge, curry, map, prop } from "https://deno.land/x/[email protected]/mod.ts";

import Either from "https://deno.land/x/[email protected]/library/Either.js";

import Task from "https://deno.land/x/[email protected]/library/Task.js";



const fetchUser = userID => Task.wrap(_ => fetch(`${URL}/users/${userID}`).then(response => response.json()));



const sayHello = compose(

  map(

    converge(

      curry((username, email) => `Hello ${username} (${email})!`),

      [

        prop("username"),

        prop("email")

      ]

    )

  ),

  fetchUser

);



// Calling `sayHello` results in an instance of `Task` keeping the function pure.

assert(Task.is(sayHello(userID)));



// Finally, calling `Task#run` will call `fetch` and return a promise

sayHello(userID).run()

  .then(container => {

    // The returned value should be an instance of `Either.Right` or `Either.Left`

    assert(Either.Right.is(container));

    // Forcing to coerce the container to string will show that the final value is our message.

    assert(container.toString(), `Either.Right("Hello johndoe ([email protected])!")`);

  });



// await sayHello(userID).run() === Either.Right(String)

```



### Using the bundle



As a convenience, when using Functional in the browser, you can use the **unminified** bundled copy (18KB gzipped).



```js

import { compose, converge, lift, map, prop } from "https://deno.land/x/[email protected]/mod.ts";

import { Either, Task } from "https://deno.land/x/[email protected]/functional.js";



const fetchUser = userID => Task.wrap(_ => fetch(`${URL}/users/${userID}`).then(response => response.json()));



const sayHello = compose(

  map(

    converge(

      curry((username, email) => `Hello ${username} (${email})!`),

      [

        prop("username"),

        prop("email")

      ]

    )

  ),

  fetchUser

);

```



---



## Either



The `Either` is a sum type similar to `Maybe`, but it differs in that a value can be of two possible types

(Left or Right). Commonly the Left type represents an error.



The `Either` type implements the following algebras:

- [x] Alternative

- [x] Comonad

- [x] Monad



### Example



```js

import Either from "https://deno.land/x/[email protected]/library/Either.js";



const containerA = Either.Right(42).map(x => x + 2);

const containerB = Either.Left(new Error("The value is not 42.")).map(x => x + 2);

const containerC = containerB.alt(containerA);



assert(Either.Right.is(containerA));

assert(containerA.extract() === 44);

assert(Either.Left.is(containerB));

assert(Either.Right.is(containerC));

```



---



Traverse is an experimental feature; The Naturility law test is failing.



---



## IO



The `IO` type represents a call to IO. Any Functional Programming purist would tell you that your functions has

to be pure... But in the real world, this is not very useful. Wrapping your call to IO with `IO` will enable you

to postpone the side-effect and keep your program (somewhat) pure.



The `IO` type implements the following algebras:

- [x] Monad



### Example



```js

import IO from "https://deno.land/x/[email protected]/library/IO.js";



const container = IO(_ => readFile(`${Deno.cwd()}/dump/hoge`))

  .map(promise => promise.then(text => text.split("\n")));

// File isn't being read yet. Still pure.



assert(IO.is(containerA));



const promise = container.run();

// Now, the file is being read.



const lines = await promise;

```



---



## Maybe



The `Maybe` is the most common sum type; it represents the possibility of a value being `null` or `undefined`.



The `Maybe` type implements the following algebras:

- [x] Alternative

- [x] Comonad

- [x] Monad



### Example



```js

import Maybe from "https://deno.land/x/[email protected]/library/Maybe.js";



const containerA = Maybe.Just(42).map(x => x + 2);

const containerB = Maybe.Nothing.map(x => x + 2);



assert(Maybe.Just.is(containerA));

assert(containerA.extract() === 44);

assert(Maybe.Nothing.is(containerB));

```



---



Traverse is an experimental feature; The Naturility law test is failing.



---



## Pair



The `Pair` type represents two values.



The `Pair` type implements the following algebras:

- [x] Bifunctor

- [x] Functor



### Example



```js

import Pair from "https://deno.land/x/[email protected]/library/Pair.js";



const pair = Pair(42, 42)

  .bimap(

    x => x * 2,

    x => x + 2

  );



assert(Pair.is(pair));

assert(pair.first === 84);

assert(pair.second === 44);

```



---



## Task



The `Task` type is similar in concept to `IO`; it helps keep your function pure when you are working with `IO`.

The biggest difference with `IO` is that this type considers Promise as first-class citizen. Also, it always resolves

to an instance of `Either`; `Either.Right` for a success, `Either.Left` for a failure.



The `IO` type implements the following algebras:

- [x] Monad



### Example



```js

import Task from "https://deno.land/x/[email protected]/library/Task.js";



const containerA = Task(_ => readFile(`${Deno.cwd()}/dump/hoge`))

  .map(text => text.split("\n"));

// File isn't being read yet. Still pure.



assert(Task.is(containerA));



const containerB = await container.run();

// Now, the file is being read.



assert(Either.Right.is(containerB));

// The call was successful!



const lines = containerB.extract();

```



The `Task` factory comes with a special utility method called `wrap`. The result of any function called with `wrap`

will be memoized allowing for safe "logic-forks".



Take the following example; `containerD` contains the raw text, `containerE` contains the text into lines and

`containerF` contains the lines in inverted order. Because `run` was called thrice, the file was read thrice. 😐



```js

let count = 0;

const containerA = Task(_ => ++count && readFile(`${Deno.cwd()}/dump/hoge`));

const containerB = containerA.map(text => text.split("\n"));

const containerC = containerB.map(lines => text.reverse());



assert(Task.is(containerA));

assert(Task.is(containerB));

assert(Task.is(containerC));



const containerD = await containerA.run();

const containerE = await containerB.run();

const containerF = await containerC.run();



assert(count === 3);

```



Definitely not what we want... Simply wrap the function and bim bam boom - memoization magic! (The file will only be

read once) 🤩



Please check-out [Functional IO](https://github.com/sebastienfilion/functional-deno-io) for more practical examples.



---



## Type factory



The Type factory can be used to build complex data structure.



```js

import { factorizeType } from "https://deno.land/x/[email protected]/library/factories.js";



const Coordinates = factorizeType("Coordinates", [ "x", "y" ]);

const vector = Coordinates(150, 200);

// vector.x === 150

// vector.y === 200

```



### Type`.from`

`Type ~> Object → t`



Create an instance of Type using an object representation.



```js

const vector = Coordinates.from({ x: 150, y: 200 });

// vector.x === 150

// vector.y === 200

```



### Type`.is`

`Type ~> Type t → Boolean`



Assert that an instance is of the same Type.



```js

Coordinates.is(vector);

// true

```



### Type`.toString`

`Type ~> () → String`



Serialize the Type Representation into a string.



```js

Coordinates.toString();

// "Coordinates"

```



### Type(a)`.toString`

`Type t => t ~> () → String`



Serialize the instance into a string.



```js

vector.toString();

// "Coordinates(150, 200)"

```



## Sum Type factory



```js

import { factorizeSumType } from "https://deno.land/x/[email protected]/library/factories.js";



const Shape = factorizeSumType(

  "Shape",

  {

    // Square :: (Coord, Coord) → Shape

    Square: [ "topLeft", "bottomRight" ],

    // Circle :: (Coord, Number) → Shape

    Circle: [ "center", "radius" ]

  }

);

```



### SumType`.from`

`SumType ~> Object → t`



Create an instance of Type using an object representation.



```js

const oval = Shape.Circle.from(

  {

    center: Coordinates.from({ x: 150, y: 200 }),

    radius: 200

  }

);

// oval.center === Coordinates(150, 200)

// oval.radius === 200

```



### SumType`.is`

`SumType ~> SumType t → Boolean`



Assert that an instance is of the same Sum Type.



```js

Shape.Circle.is(oval);

// true

```



### SumType`#fold`



```js

Shape.prototype.translate = function (x, y, z) {

  return this.fold({

    Square: (topleft, bottomright) =>

      Shape.Square(

        topLeft.translate(x, y, z),

        bottomRight.translate(x, y, z)

      ),



    Circle: (centre, radius) =>

      Shape.Circle(

        centre.translate(x, y, z),

        radius

      )

  })

};

```



### SumType(a)`.toString`

` SumType t => t ~> () → String`



Serialize the instance into a string.



```js

oval.toString();

// "Shape.Circle(Coordinates(150, 200), 200)"

```



@function

@name factorizeType

@module functional/SumType



@description Factorize a Type Representation.

@param {String} typeName

@param {String[]} propertyNameList

@return {Function}



@example

const Coordinates = factorizeType("Coordinates", [ "x", "y" ]);

const vector = Coordinates(150, 200);

// vector.x === 150

// vector.y === 200



---



## Utilities



### `assertIsArray`

`* → Boolean`



### `assertIsBoolean`

`* → Boolean`



### `assertIsFunction`

`* → Boolean`



### `assertIsInstance`

`* → Boolean`



### `assertIsNull`

`* → Boolean`



### `assertIsNumber`

`* → Boolean`



### `assertIsObject`

`* → Boolean`



### `assertIsRegex`

`* → Boolean`



### `assertIsString`

`* → Boolean`



### `assertIsUndefined`

`* → Boolean`



### `decodeRaw`

`Uint8Array → String`



### `encodeText`

`String → Uint8Array`



### `alt`

`Alt a → Alt b → Alt a|b`



This function takes a container of any type and, an Alternative functor. Then it returns either the container or the

alternative functor.

The function is in support of the [Alt algebra](https://github.com/fantasyland/fantasy-land#alt).



```js

import Either from "https://deno.land/x/[email protected]/library/Either.js";

import { alt } from "https://deno.land/x/[email protected]/library/utilities.js";



const container = alt(Either.Right(42), Either.Left("Not the meaning of life"));



assertEquals(container.extract(), 42);

```



### `chainLift`

`(a → b → c) → Chainable a → Functor b → Chainable c`



This function is similar to [`lift`](https://ramdajs.com/docs/#lift) but is chainable.



```js

import Task from "https://deno.land/x/[email protected]/library/Task.js";

import { chainLift } from "https://deno.land/x/[email protected]/library/utilities.js";



const hogeFuga = useWith(

  chainLift(curry((x, y) => Task.of(x * y))),

  [

    x => Task.of(x),

    x => Task.of(x)

  ]

);



const container = await hogeFuga(42, 24).run();



const value = safeExtract("Failed.", container);



assertEquals(value, 1008);

```



### `chainRec`

`ChainRec r => ((a → c, b → c, a) → r c) → a → r b`



This function is a combinator for the [`chainRec` algebra](https://github.com/fantasyland/fantasy-land#chainrec).

It takes a ternary function, an initial value and, a chainable recursive functor.



```js

import Task from "https://deno.land/x/[email protected]/library/Task.js";

import { chainRec } from "https://deno.land/x/[email protected]/library/utilities.js";



const multiplyAll = curry((x, n) => chainRec(

  (Loop, Done, cursor) =>

    cursor === n ? Done(Pair(cursor, null)) : Loop(Pair(cursor + 1, Task.of([ x * (cursor + 1) ]))),

  0

));



const container = await multiplyAll(42, 10)(Task.of([ 0 ])).run();



const value = safeExtract("Failed.", container);



assertEquals(value, [ 0, 42, 84, 126, 168, 210, 252, 294, 336, 378, 420 ]);

```



### `evert`

`Applicative a => a → a[] → a`



This function takes a type constructor and, a list of Applicative functor and evert it; effectively making an Applicative

functor of a list of value.



```js

import Task from "https://deno.land/x/[email protected]/library/Task.js";

import { evert } from "https://deno.land/x/[email protected]/library/utilities.js";



const container = await evert(Task, [ Task.of(42), Task.of(32), Task.of(24) ]).run();



const list = safeExtract("Failed.", container);



assertEquals(list, [ 42, 32, 24 ]);

```



### `log`

`String → a → a`



This function is a composable `console.debug`. It takes a message, a value and, return the value.



### `runSequentially`

`Chain c => (...c) → c`



This function takes n Chainable functor and chain them automatically.



```js

import Task from "https://deno.land/x/[email protected]/library/Task.js";

import { runSequentially } from "https://deno.land/x/[email protected]/library/utilities.js";



const fuga = converge(

  runSequentially,

  [

    x => Task.of(x * 2),

    x => Task.of(x + 2)

  ]

);



const container = await fuga(42).run();



const value = safeExtract("Failed.", container);



assertEquals(value, 44);

```



### `safeExtract`

`String → Either a → a`



This function takes a message and an Either container; if the container is `Either.Right`, the value will be

returned. But if the container is `Either.Left`, it will throw an error with the message passed.



### `stream`

`((a, b) → a) → a → AsyncIterable b → a`



---



## TypeScript



You can import any types or the factories through `mod.ts`.



```ts

import {

  Either,

  IO,

  Maybe,

  Pair,

  Task,

  factorizeType,

  factorySumType

} from "https://deno.land/x/[email protected]/mod.ts";

```



Or, you can import individual sub-module with the appropriate TypeScript hint in Deno.



```ts

// @deno-types="https://deno.land/x/[email protected]/library/Either.d.ts"

import Either from "https://deno.land/x/[email protected]/library/Either.js";

```

 

---



## Contributing



We appreciate your help! Please, [read the guidelines](./CONTRIBUTING.md).



## License



Copyright © 2020 - Sebastien Filion



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.