kurrie

JavaScript's highly optimized and speedy currying function.

Install

npm install kurrie --save

Distributions:

• dist/kurrie.min.js is UMD and can be used in browsers.
• dist/kurrie.js is CommonJS, and is used by node.

Motivation

Mostly for fun. However, as I was comparing kurrie to other curry functions available on npm, I found that most of the larger libraries were pretty slow by comparison. kurrie focuses on flexibility without sacrificing speed. See the benchmarks below.

Usage

kurrie curries functions with support for both placeholders and partial application.
This means that the all of the various calls to sum below will evaluate to 6.

import kurrie from 'kurrie';
 
const sum = kurrie ((a, b, c) => a + b + c);
 
sum (1, 2, 3);
sum (1, 2) (3);
sum (1) (2, 3);
sum (1) (2) (3);
sum (1, _, 3) (2);
sum (_, 2) (1) (3);
sum (_, 2, 3) (1);
sum (_, 2) (_, 3) (1);
sum (_, _, 3) (1) (2);
sum (_, _, 3) (1, 2);
sum (_, _, 3) (_, 2) (1);

Basic Currying

Adding to any array of numbers.

import kurrie from 'kurrie';
 
const map = kurrie ((iteratee, list) => list.map (iteratee));
const sum = kurrie ((x, y) => x + y);
 
const inc = sum (1);
 
map (inc, [1, 2, 3]);      // => [2, 3, 4]
map (inc) ([1, 2, 3]);     // => [2, 3, 4]
 
map (sum (2)) ([1, 2, 3]); // => [3, 4, 5]
 

Partial Placeholders

You can use the export _ as a placeholder value, which means "skip" the argument and expect it in the next invocation.

import kurrie, { _ } from 'kurrie';
 
const map = kurrie ((iteratee, list) => list.map (iteratee));
const forEachUser = map (_, ['John', 'Ed', 'Albert']);
 
const greet = kurrie ((greeting, name) => `${greeting} ${name}!`);
 
forEachUser (greet ('Hello'))  // => ['Hello John!', 'Hello Ed!', 'Hello Albert!']

Alternatively, since _ is typically reserved for lodash, kurrie also exports __ as an alternative placeholder value.

API

kurrie({function} fn[, {Object=} options]) => {function}

The default export. Curries the given function up to arity.

Options:

Property	Default	Description
arity	fn.length	The number of arguments that must be met before invoking fn.
capped	true	If true, the number of arguments passed to fn will never exceed arity. If false, arguments beyond arity may "leak" into invocations.

You should note the behavior of Function#length in regard to rest and default parameters! See MDN for documentation on Function#length.

For example:

If capped is false

const x = kurrie ((x, y = 3) => [x, y]);
x(1, 2); // => [1, 2];

If capped is true (default)

const pairs = (x, y = 3) => [x, y];
paris.length // => 1
 
const x = kurrie (pairs);
x(1, 2); // => [1, 7];

Since y is a default value, it's not included in pairs.length. To get expected results, set the arity of the curried version of pairs.

const x = kurrie (pairs, { arity: 2 });
 
x(1, 2); // => [1, 2];
x(1)(2); // => [1, 2];
x(1)(undefined); // => [1, 3];

kurrie.to({number} arity, {function} fn[, {boolean=} capped=true]) => {function}

An alias for the kurrie method that is arity first.
kurrie.to offers a cleaner syntax when you need to specify an arity value.

const sum = kurrie.to (3, function (a, b, c = 3) {
  return a + b + c;
});
 
sum (1) (2) (undefined); // => 6
sum (1) (2) (10);        // => 13

kurrie.proto({function} fn[, {Object=} options]) => {function}

A convenience method to curry prototype methods.
Curries the given prototype method passing the last argument as the this value.

Options:

Property	Default	Description
arity	fn.length + 1	The number of arguments that must be met before invoking fn.
capped	true	If true, the number of arguments passed to fn will never exceed arity. If false, arguments beyond arity may "leak" into invocations.
thisArgPosition	arity - 1	The argument to use as this when applying arguments to the prototype method. For example, with Array#filter: Array.prototype.filter.apply(arguments[thisArgPosition], args);. This defaults to the last argument passed to the function (i.e. arity - 1).

const map = kurrie.proto (Array.prototype.map);
map (x => x * 2) ([1, 2, 3]); // => [2, 4, 6]
 
const toUpperCase = kurrie.proto (String.protoype.toUpperCase);
toUpperCase ('foo') // => 'FOO'
 
const replace = kurrie.proto (String.protoype.replace);
const swap = replace (/^hello/, 'goodbye');
swap ('hello world!'); // 'goodbye world!'

An example of overriding the arity with kurrie.proto:

// Default
const slice = kurrie.proto (String.prototype.slice);
slice(0)(3)('foobar'); // => 'foo'
 
// Omitting slice's "end" argument
const sliceFrom = kurrie.proto (String.prototype.slice, { arity: 2 });
sliceFrom(2)('foobar'); // => 'obar'

isCurried({function} fn) => {boolean}

Determines is fn is a curried function.
Returns true if the supplied function is curried using kurrie, false otherwise.

import kurrie, { isCurried } from 'kurrie';
 
isCurried (kurrie (() => { ... }))  // => true
isCurried (() => { ... })           // => false

getSourceFunction({function} fn) => {function|undefined}

Returns the source (original, uncurried) version of a curried function.
Some libraries call this "uncurry".

import kurrie, { getSourceFunction, uncurry } from 'kurrie';
 
const sum = kurrie ((x, y) => x + y);
sum(1)(2) // => 3
 
const uncurried = getSourceFunction (sum);
uncurried(1, 2) // => 3
uncurried(1)(2) // => Error
 
// `uncurry` is also provided as an alias to `getSourceFunction`
const uncurried = uncurry (sum);

curryTo

Named export for kurrie.to.

import { curryTo } from 'kurrie';
 
const sum = curryTo (3, function (a, b, c = 3) { ... });

curryProto

Named export for kurrie.proto.

import { curryProto } from 'kurrie';
 
const slice = curryProto (Array.prototype.slice);
slice (0, 2) ([0, 1, 2, 3]) // => [0, 1, 2]

Benchmarks

Libraries were compared over a series of 26 different tests (see below) using the Benchmark Suite. See bench.js in the root of this repo to view the benchmark tests.

The following libraries were compared to kurrie:

• Lodash
• Rambda
• Curry
• Curriable
• Kurry

Average Operations Per Second

Rank	Library	Average Operations Per Second	% Avg
1	Kurrie	4,209,498	177%
2	Curriable	3,480,912	146%
3	Rambda	2,222,195	94%
4	Curry	1,621,990	69%
5	Lodash	1,384,082	59%
6	Kurry	1,354,722	57%

Benchmarks were performed on an 2.8 GHz Intel Core i7 MacBook Pro, 16GB Memory using Node.js version 8.7.0.

Benchmark Test Types

• Curried function initialization (creation).
• Calling a nullary curried function.
• Calling a unary curried function.
• Calling a binary curried function (multiple call configurations).
• Calling a trinary curried function (multiple call configurations).
• Calling a 20-ary curried function (multiple call configurations).
• Calling a curried function that reference this.
• Calls without arguments (i.e. foo()()()(1)()(2)).
• Multi-curried called (i.e. map(sum(1))([1, 2 ,3])).
• Calling curried functions with placeholders (multiple configurations).
• Currying already curried functions.