/HigherOrderFunctions.html

## HigherOrderFunctions.html
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        Functional Programming Samples</h1>
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    <ol id="qunit-tests">
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    <div id="qunit-fixture">
    </div>
    <script type="text/javascript">
        /* map and reduce EcmaScript3 implementation */
        var map = Array.prototype.map
            ?
            function (a, fn) { return a.map(fn); }
            :
            function (a, fn) {
                var result = [];
                for (var i = 0; i < a.length; i++) {
                    if (i in a) result[i] = fn.call(null, a[i], i, a);
                }
                return result;
            };

        var reduce = Array.prototype.reduce
            ?
            function (a, fn, initial) {
                if (arguments.length > 2)
                    return a.reduce(fn, initial);
                else
                    return a.reduce(fn);
            }
            :
            function (a, fn, initial) {
                var i = 0;
                var l = a.length;
                var accum;

                if (arguments.length > 2)
                    accum = initial;
                else {
                    if (l == 0) throw TypeError();
                    while (i < l) {
                        if (i in a) {
                            accum = a[i++];
                            break;
                        }
                        else
                            i++;
                    }
                    if (i == l) throw TypeError();
                }

                while (i < l) {
                    if (i in a)
                        accum = fn.call(undefined, accum, a[i], i, a);
                    i++
                }

                return accum;
            };


        /* higher-order functions */

        var isEven = function (input) {
            return input % 2 === 0;
        }

        var not = function (f) {
            return function () {
                return !f.apply(this, arguments);
            };
        }

        var isOdd = not(isEven);

        /* */

        var isPositive = function (input) {
            return input > 0;
        };

        var isZero = function (input) { return input === 0; };

        var and = function (f, g) {
            return function () {
                return f.apply(this, arguments) &&
                    g.apply(this, arguments);
            };
        };

        var isNegative = and(not(isPositive), not(isZero));

        /* */
        var square = function (input) { return input * input };
        var sum = function (a, b) { return a + b };
        var compose = function (f, g) {
            return function () {
                return f.call(this, g.apply(this, arguments));
            };
        };
        var squareOfSum = compose(square, sum);

        /* */
        var mapper = function (f) {
            return function (a) { return map(a, f); };
        };

        var incrementer = mapper(function (input) { return input + 1 });

        /* tests */
        $(function () {

            module("Higher-order functions sample");

            test("isOdd/isEven", function () {
                ok(!isOdd(2), "isOdd, passing 2, returns false.");
                ok(isEven(2), "isEven, passing 2, returns true.");
            });

            test("isNegative/isZero/isPositive", function () {
                ok(isNegative(-1), "isNegative, passing -1, returns true.");
                ok(!isNegative(0), "isNegative, passing 0, returns false.");
                ok(!isNegative(1), "isNegative, passing 1, returns false.");
            });

            test("composing", function () {
                equals(squareOfSum(6, 3), 81, "squareOfSum, passing 6 and 3, returns 81.");
            });

            test("mapper", function () {

                ok(incrementer([4, 5, 6]).toString() == [5, 6, 7], "incrementer, passing [4,5,6], returns [5,6,7]");
            });
        });
    </script>
</body>
</html>
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	<link rel="stylesheet" href="http://code.jquery.com/qunit/git/qunit.css" type="text/css" />
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	<script type="text/javascript" src="http://code.jquery.com/qunit/git/qunit.js"></script>
	</head>
	<body>
	<h1 id="qunit-header">
	Functional Programming Samples</h1>
	<h2 id="qunit-banner">
	</h2>
	<div id="qunit-testrunner-toolbar">
	</div>
	<h2 id="qunit-userAgent">
	</h2>
	<ol id="qunit-tests">
	</ol>
	<div id="qunit-fixture">
	</div>
	<script type="text/javascript">
	/* map and reduce EcmaScript3 implementation */
	var map = Array.prototype.map
	?
	function (a, fn) { return a.map(fn); }
	:
	function (a, fn) {
	var result = [];
	for (var i = 0; i < a.length; i++) {
	if (i in a) result[i] = fn.call(null, a[i], i, a);
	}
	return result;
	};

	var reduce = Array.prototype.reduce
	?
	function (a, fn, initial) {
	if (arguments.length > 2)
	return a.reduce(fn, initial);
	else
	return a.reduce(fn);
	}
	:
	function (a, fn, initial) {
	var i = 0;
	var l = a.length;
	var accum;

	if (arguments.length > 2)
	accum = initial;
	else {
	if (l == 0) throw TypeError();
	while (i < l) {
	if (i in a) {
	accum = a[i++];
	break;
	}
	else
	i++;
	}
	if (i == l) throw TypeError();
	}

	while (i < l) {
	if (i in a)
	accum = fn.call(undefined, accum, a[i], i, a);
	i++
	}

	return accum;
	};


	/* higher-order functions */

	var isEven = function (input) {
	return input % 2 === 0;
	}

	var not = function (f) {
	return function () {
	return !f.apply(this, arguments);
	};
	}

	var isOdd = not(isEven);

	/* */

	var isPositive = function (input) {
	return input > 0;
	};

	var isZero = function (input) { return input === 0; };

	var and = function (f, g) {
	return function () {
	return f.apply(this, arguments) &&
	g.apply(this, arguments);
	};
	};

	var isNegative = and(not(isPositive), not(isZero));

	/* */
	var square = function (input) { return input * input };
	var sum = function (a, b) { return a + b };
	var compose = function (f, g) {
	return function () {
	return f.call(this, g.apply(this, arguments));
	};
	};
	var squareOfSum = compose(square, sum);

	/* */
	var mapper = function (f) {
	return function (a) { return map(a, f); };
	};

	var incrementer = mapper(function (input) { return input + 1 });

	/* tests */
	$(function () {

	module("Higher-order functions sample");

	test("isOdd/isEven", function () {
	ok(!isOdd(2), "isOdd, passing 2, returns false.");
	ok(isEven(2), "isEven, passing 2, returns true.");
	});

	test("isNegative/isZero/isPositive", function () {
	ok(isNegative(-1), "isNegative, passing -1, returns true.");
	ok(!isNegative(0), "isNegative, passing 0, returns false.");
	ok(!isNegative(1), "isNegative, passing 1, returns false.");
	});

	test("composing", function () {
	equals(squareOfSum(6, 3), 81, "squareOfSum, passing 6 and 3, returns 81.");
	});

	test("mapper", function () {

	ok(incrementer([4, 5, 6]).toString() == [5, 6, 7], "incrementer, passing [4,5,6], returns [5,6,7]");
	});
	});
	</script>
	</body>
	</html>
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