jsFunCurry.js

/**
 * A dirty hack to achieve true function currying in javascript
 **/



var curry = (function() {
/* ---> 
 * wrap everything in a private scope;
 */

/* Generates an array of unique named variable/argument names
 * of length k.
 */
var identifiers="abcdefghijklmnopqrstuvwxyz";
function named_args(k) {

  var args=[],n = identifiers.length;
  while(k--) {
    args.push(k.toString(n).split("").map(function(x) {
      return identifiers.charAt(parseInt(x, n))
    }).join(""))
  }
  return args
}

/* It takes a function f(x) which returns another function g(y) as a result, 
 * and yields a new function f′(x,y) which takes a number of additional 
 * parameters and applies them to the function returned by function f. 
 * The process can be iterated if necessary.
 */
function uncurry(fn) {
  return function() {
    var i, f, len = arguments.length;
    f = fn;
    for(i=0;i<len;i++) {
      f = f(arguments[i])
    }
    return f;
  }
}
/* Transforming a function that takes multiple arguments in such a way 
 * that it becomes a chain of functions, [f(x,y,z) => g(x)(y)(z)] 
 * each with a single argument, then uncurry the output function,
 * so that it can be used with more flexibility, taking any number (less
 * than the length of the chain of functions), and return the remainder of
 * the chain. 
 */
function curry(fn) {
  var len = fn.length, 
      args = named_args(len),
      body = 'return fn('+args.join(',')+')',
      arg,
      f;
  // only works on functions with more than one named (of known number) arguments
  if (len < 2) return fn;
  // has to use eval for function def, as the "Function" constructor
  // does not create a nice closure, which we need so that the returned 
  // function chain has access to the original function
  // see: http://www.bennadel.com/blog/1909-javascript-function-constructor-does-not-create-a-closure.htm
  eval('f=function ('+args.pop()+'){'+ body + '}');
  while(arg=args.pop()) {
    eval('f=function ('+arg+'){return uncurry('+f.toString()+ ')}')
  }
  return uncurry(f)
}
return curry;
  
//<--- 
})();


// basic examples

var sum6 = function(x,y,z,u,v,w) {
  return x+y+z+u+v+w;
};

var sum6_ = curry(sum6);

sum6_(1)(1)(1)(1)(1)(1) === 6; // true
sum6_(1,1,1,1,1,1) === 6 // true
sum6_(1,1,1)(1,1,1) === 6 //true

var sum5_ = sum6_(2),
    sum4_ = sum6_(2,3);
    sum4__ = sum6_(2)(3); // they are all functions
sum5_(1,1,1,1,1) === 7; // true
sum4_(1,1,1,1) === 9; // true
sum4__(1)(1)(1,1) === 9; //true

// more "useful" examples

var _reduce = curry(function (fn, memo, arry) {
  return arry.reduce(fn, memo)
});

var sum = _reduce(function(s, x){ return s+x }, 0);
var product = _reduce(function(p, x){ return p*x })(1);

sum([1,2,3,4]) === 10 // true
product([1,2,3,4]) === 24 // true

//

var each = curry(function(fn, arry) {
  return arry.forEach(fn);
});

var attachElement = curry(function(tagName, parentNode, className, id, html) {
    var e = document.createElement(tagName);
    e.id = id;
    e.className = className;
    e.innerHTML = html;
    parentNode.appendChild(e);
    return e;
});

var createDiv = attachElement('DIV', document.body);

var createColorfulDivs = each(function(d) {
  createDiv(d.cls, d.id, d.content);
});

var data=[{ id:1, content: "I am red.", cls: "red"},
          { id:2, content: "I am blue.", cls: "blue"},
          { id:3, content: "I am yellow.", cls: "yellow"},
          { id:4, content: "I am black.", cls: "black"}];

createColorfulDivs(data);