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. 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:

// 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 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:

// 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:

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

3. Partial application under purry's auspicious implementation has an additional feature in addition to pinning left-to-right pins or right-to-left: holes. Holes allow saving arguments against any arbitrary point in the parameter list. Behold a contrived example:

// 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. Holes could help:
var psmith = person(_, 'Smith', _)

[['Sarah', 30], ['Ryan', 32], ['Timmy', 2]].map(psmith)
// [{ first: 'Sarah', last: 'Smith', age: 30 }, ...]

Learn more in @fogus's tour de force Functional JavaScript in the "Partial Application" section in Chapter 5. Function-Building Functions. It includes many examples, use-cases, diagrams, etc. Note he does not discuss holes as that is a purry-only feature. Learn more about holes 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.