javascript-patterns/function-patterns/currying.html at master · cyberpython/javascript-patterns · GitHub

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<!doctype html>
<html lang="en">
<head>
<title>JavaScript Patterns</title>
<meta charset="utf-8">
</head>
<body>
<script>
/* Title: Currying
   Description: used to create new functions dynamically by partially applying a set of arguments
*/

/***
 function application
 ***/
// define a function
var sayHi = function (who) {
  return "Hello" + (who ? ", " + who : "") + "!";
};

// invoke a function
sayHi(); // "Hello"
sayHi('world'); // "Hello, world!"

// apply a function
sayHi.apply(null, ["hello"]); // "Hello, hello!"

var alien = {
  sayHi: function (who) {
    return "Hello" + (who ? ", " + who : "") + "!";
  }
};

alien.sayHi('world'); // "Hello, world!"
sayHi.apply(alien, ["humans"]); // "Hello, humans!"

// the second is more efficient, saves an array
sayHi.apply(alien, ["humans"]); // "Hello, humans!"
sayHi.call(alien, "humans"); // "Hello, humans!"

/***
 partial application
 ***/

// for illustration purposes
// not valid JavaScript

// we have this function
function add(x, y) {
  return x + y;
}

// and we know the arguments
add(5, 4);

// step 1 -- substitute one argument
function add(5, y) {
  return 5 + y;
}

// step 2 -- substitute the other argument
function add(5, 4) {
  return 5 + 4;
}

/***
 currying
 ***/

// a curried add()
// accepts partial list of arguments
function add(x, y) {
  var oldx = x, oldy = y;
  if (typeof oldy === "undefined") { // partial
    return function (newy) {
      return oldx + newy;
    }
  }
  // full application
  return x + y;
}

// test
typeof add(5); // "function"
add(3)(4); // 7

// create and store a new function
var add2000 = add(2000);
add2000(10); // 2010

function schonfinkelize(fn) {
  var slice = Array.prototype.slice,
      stored_args = slice.call(arguments, 1);
  return function () {
    var new_args = slice.call(arguments),
        args = stored_args.concat(new_args);
    return fn.apply(null, args);
  };
}

// reference
// http://www.jspatterns.com/
// http://shop.oreilly.com/product/9780596806767.do?sortby=publicationDate
</script>
</body>
</html>