curry-arity

Simple, tiny curry() and curryN() functions.

Both can take functions of any arity, there are no limits.

Resulting functions will always have the correct arity (length property).

This library does not use eval(), new Function() or any dynamic code evaluation.

Examples

const f = (a, b, c) => a + b + c;

const add = curry(f);

add.length; // 3
add(10).length; // 2
add(10)(20).length; // 1

add(10)(20)(30); // 60
add(10, 20)(30); // 60
add(10)(20, 30); // 60
add(10, 20, 30); // 60

/* reusable */
const addTen = add(10); 
addTen(20)(30); // 60
addTen(40)(50); // 100

Only the parameters before the first one with a default value are counted:

const add = curry((a, b, c = 30) => a + b + c);

add.length; // 2
add(10)(20); // 60
// add(10)(20)(70) would throw TypeError

/* you can pass additional arguments in the final call */
add(10)(20, 70); // 100

You can also specify arity using curryN() instead of curry():

const add = curryN(3, (a, b, c = 30) => a + b + c);

add.length; // 3
add(10)(20)(70); // 100

/* undefined always triggers the default value */
add(10)(20)(undefined); // 60

Another example with curryN():

const add = (...args) => args.reduce((a, b) => a + b);

curryN(2, add).length;  // 2
curryN(2, add)(10)(20); // 30

curryN(3, add).length;  // 3
curryN(3, add)(10)(20)(70); // 100

Curried functions also correctly handle implicit this:

const obj = {
  a: 10,
  addMe: curry(function (b, c) { return this.a + b + c; })
}  

/* 'this' from the first call (obj.addMe(20)) is always used */
obj.addMe(20)(30); // 60 

How it works

Using Object.defineProperty() on created function objects. The original function object is not changed in any way.

By the ES6 specification, function.length is configurable. It wasn't configurable in ES5.

Supported Environments

This library will not work in old ES5 browsers, namely IE11. By design, functions will throw if the length cannot be set, as the correct arity is a part of the API.

The code is not transpiled to ES5, as the ES6 version is more efficient and the library wouldn't work in all ES5 browsers anyway. So, supported environments are:

• Node >= 6
• Browsers that support basic ES6 syntax

Installation and Usage

Node

$ npm install curry-arity

const { curry, curryN } = require('curry-arity');

const f = (a, b, c = 30) => a + b + c;

const fc = curry(f);
console.log(fc(10)(20)); // 60

const fc3 = curryN(3, f);
console.log(fc3(10)(20)(70)); // 100

Browser Script

Unminified (~600B):

<script src="https://unpkg.com/[email protected]/dist/curryarity.js"></script>

or

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/curryarity.js"></script>

Minified (~250B):

<script src="https://unpkg.com/[email protected]/dist/curryarity.min.js"></script>

or

<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/curryarity.min.js"></script>

The script creates a global variable CurryArity:

const f = (a, b, c = 30) => a + b + c;

const fc = CurryArity.curry(f);
console.log(fc(10)(20)); // 60

const fc3 = CurryArity.curryN(3, f);
console.log(fc3(10)(20)(70)); // 100

You can also install the package and take the scripts from the dist folder.

ES Module

$ npm install curry-arity

ES module: ./node_modules/curry-arity/src/index.js

If you are using Webpack, Rollup or any tool that reads from pkg.module, then simply:

import { curry, curryN } from 'curry-arity';

const f = (a, b, c = 30) => a + b + c;

const fc = curry(f);
const fc3 = curryN(3, f);

and it will use the ES module directly, instead of the CommonJS version.

API

curry(f)

Returns curried f, with the original arity.

f

Function of any arity.

curryN(n, f)

Returns curried f, with the specified arity.

n

Arity of the resulting function. Should be a non-negative integer.

It can be less, equal or greater than the original arity.

f

Function of any arity.

By design, the functions do not validate provided arguments.

About

Author

Milos Djermanovic

License

MIT License