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https://github.com/jasonkuhrt/purry

Symbiotic, high-performance currying and partial application
https://github.com/jasonkuhrt/purry

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Symbiotic, high-performance currying and partial application

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# purry [![Build Status](https://travis-ci.org/jasonkuhrt/purry.png?branch=master)](https://travis-ci.org/jasonkuhrt/purry)



[![browser support](https://ci.testling.com/jasonkuhrt/purry.png)

](https://ci.testling.com/jasonkuhrt/purry)



  Symbiotic, performent **currying** and **partial application**.



## Installation



Server | Client

-------|--------

`npm install --save purry` | `bower install --save purry` or `component install jasonkuhrt/purry`



## Guide



Purry greatly facilitates use of and interopability between two helpful techniques that come from the world of functional programming: Currying, and Partial Application. If these concepts are not familiar to you go read their [background](#background). Purry docs assume fluency in the topics.



## Background



##### Currying

The act of supplying fewer arguments to a function `f1` than it is has parameters which (given `f1` is curried) returns a new function `f2` whose parameters are those that were not argued against `f1` before. For example:

```js

// Imagine f1 is this add function:



add(1, 2)

// 3



// f2 would be derived like so:

var add1 = add(1)



// Ready to be used in high-order contexts, etc.:

[1,2,3,4,5].map(add1)

// [2,3,4,5,6]

```

Canocially, currying works left-to-right.



Learn more in @fogus's tour de force [Functional JavaScript](http://www.functionaljavascript.com/) in the "Currying" section in Chapter 5. Function-Building Functions. It includes many examples, use-cases, diagrams, etc.



In lieu of buying the book try: http://programmers.stackexchange.com/questions/185585/what-is-the-advantage-of-currying



##### Partial Application

The act of "pinning" arguments to a function's parameters. Differences from currying:



1. Partial application may work from left-to-right OR right-to-left whereas currying is strictly left-to-right. The direction simply means whether the partially-applied arguments will be prepended or appended to the arguments given to the function at invoke-time. Notice how right-to-left is different and sometimes needed:

  ```js

  // First, regular left-to-right stuff:

  var subFrom10 = sub(10) // currying example

  var subFrom10Alt = sub(10,___) // partial application example



  subFrom10(6) // 4

  subFrom10Alt(6) // 4



  // But how do we create a sub10 function?

  // We can with right-to-left partial application:

  var sub10 = sub(___,10)

  sub10(6) // -4

  ```



2. Partial application necessarially implies an invocation delay whereas currying does not. Notice how currying invokes the function as soon as all parameters are argued:

  ```js

  add(1)(2) // 3

  add(1,___)(2,___)() // 3

  ```



3. Partially applying may also work through the use of wild-cards. Wild-cards allow arbitrary parameters to be partially applied; Example:

  ```js

  // Assume a "person" function that accepts three

  // parameters: first name, last name, age.

  person('John', 'Smith', 30)

  // { first: 'John', last: 'Smith', age: 30 }



  // When dealing with families, repeating the last

  // name can be redundant. Wild-cards could help:

  var psmith = person(_, 'Smith', _)



  [['Sarah', 30], ['Ryan', 32], ['Timmy', 2]].map(psmith)

  // [{ first: 'Sarah', last: 'Smith', age: 30 },

  //  { first: 'Ryan', last: 'Smith', age: 32 },

  //  { first: 'Timmy', last: 'Smith', age: 2 }

  // ]

  ```



Learn more in @fogus's tour de force [Functional JavaScript](http://www.functionaljavascript.com/) in the "Partial Application" section in Chapter 5. Function-Building Functions. It includes many examples, use-cases, diagrams, etc. Note he does not discuss wild-cards as that is a purry-specific feature. Learn more about wild-cards from Purry's own docs.



## Roadmap

  I am actively working on this project. I hope to release a genuinely useful iteration in 2014. Contributions and collaborations are more than welcomed. See the tests for what is currently possible, they are truth.