javascript functional programing example

functional_programing.js

/** functional.js **/

function flip (func) {
  // preserve f
  // construct g
  return function() {
    var args = Array.prototype.slice.call(arguments);
    // flip arguments when called
    return func.apply(null, args.reverse());
  };
}
 
function asArray(quasiArray, start) {
  var result = [];
  for (var i = (start || 0); i < quasiArray.length; i++)
    result.push(quasiArray[i]);
  return result;
}
 
function partial(func) {
  var fixedArgs = asArray(arguments, 1);
  return function(){
    return func.apply(null, fixedArgs.concat(asArray(arguments)));
  };
}
 
function compose(func1, func2) {
  return function() {
    return func1(func2.apply(null, arguments));
  };
}

function wrap(func1, func2) {
	return function() {
 
		var arr = [];
		arr.push(func2);
		arr = arr.concat(asArray(arguments));
		
		var fun = partial.apply(null, arr);
		func1.call(null, fun);
	};
}

var flow = flip(compose);


/** utils.js **/
function log(x) {
  console.log(x);
}

function add(x, y) {
  return x + y;
}

function sub(x, y) {
  return x - y;
}

function multiple(x, y) {
  return x * y;
}

function div(x, y) {
  return x / y;
}

var newSetTimeout = flip(setTimeout); //newSetTimeout(timeout, func)



/** example 1 **/

var double = partial(multiple, 2); //double(int)

var add_and_double = compose(double, add);

var result = add_and_double(1, 2);

log(result);



/** example 2 **/

var delay = partial(newSetTimeout, 1000); //delay(func)

var logDiv = flow(div, log); //divAndLog(x, y)

var delayDiv = wrap(delay, logDiv);  //delayDiv(x, y)

delayDiv(1, 2);