index.js

//. # Callgebra
//.
//. The little algebra of callbacks.
//.
//. ## Introduction
//.
//. This package exports functions for composing callbacks. You can read
//. about the idea in my [Medium post about composable callbacks][1].
//.
//. ## Usage
//.
//. ### Node
//.
//. ```console
//. $ npm install --save callgebra
//. ```
//.
//. On Node 12 and up, this module can be loaded directly with `import` or
//. `require`. On Node versions below 12, `require` or the [esm][]-loader can
//. be used.
//.
//. ```js
//. import {of, callback} from 'callgebra';
//. callback (console.log) (of (42));
//. ```
//.
//. ### Deno and Modern Browsers
//.
//. You can load the EcmaScript module from various content delivery networks:
//.
//. - [Skypack](https://cdn.skypack.dev/callgebra@2.1.0)
//. - [JSPM](https://jspm.dev/callgebra@2.1.0)
//. - [jsDelivr](https://cdn.jsdelivr.net/npm/callgebra@2.1.0/+esm)
//.
//. ### Old Browsers and Code Pens
//.
//. There's a [UMD][] file included in the NPM package, also available via
//. jsDelivr: https://cdn.jsdelivr.net/npm/callgebra@2.1.0/dist/umd.js
//.
//. This file adds `flutureProject` to the global scope, or use CommonJS/AMD
//. when available.
//.
//. ```js
//. const {of, callback} = require ('callgebra');
//. callback (console.log) (of (42));
//. ```
//.
//. ## API
//.
//. ```hs
//. type Callback a b = (b -> a) -> a
//. ```

// thrush :: a -> (a -> b) -> b
const thrush = x => f => f (x);

//# of :: a -> Callback b a
//.
//. Creates a callback for a given return value.
export const of = thrush;

//# chain :: (a -> Callback c b) -> Callback c a -> Callback c b
//.
//. Sequence two callback-accepting functions.
export const chain = f => m => c => m (x => f (x) (c));

//# map :: (a -> b) -> Callback c a -> Callback c b
//.
//. Modify the return value of a callback.
export const map = f => chain (x => thrush (f (x)));

//# ap :: Callback c (a -> b) -> Callback c a -> Callback c b
//.
//. Apply the function returned by one callback to the value returned by
//. another.
export const ap = mf => mx => chain (f => map (f) (mx)) (mf);

//# callback :: (a -> b) -> Callback b a -> b
//.
//. Given a function and a Callback, runs the Callback using the function.
export const callback = thrush;

//. [1]: https://medium.com/@avaq/composable-callbacks-81c84f0324
//. [esm]: https://github.com/standard-things/esm
//. [UMD]: https://github.com/umdjs/umd