Drew LeSueur drewlesueur

How to Generate the Y-Combinator in CoffeeScript

Problem

For fun, let's say you are programming in a language that doesn't allow variable assignments and you still want to make a recursive function. Although you can't assign variables, you can use functions (and enclosed function arguments). Can you make a function recursive without calling it by name?

Lets try implementing the factorial function. First with a function calling itself by name, then with a funtion that never calls itself by name

Here is the implementation of factorial that calls itself by name. It's a simple recursive function

	# normal factorial
	factorial = (x) ->
	if x == 1 then return 1
	return x * factorial(x - 1)
	console.log factorial(6) #720


	# new factorial that doesn't reference itself
	factorialGenerator = (fac) ->
	(x) ->

	// code taken from visionmedias node-querystring
	var qs = (function () {
	var qs = {}
	/**
	* Object#toString() ref for stringify().
	*/

	var toString = Object.prototype.toString;

	/**

	// alternate to imagecreatefrom...

	$ch = curl_init();
	curl_setopt($ch, CURLOPT_URL, $url);
	curl_setopt($ch, CURLOPT_HEADER, 0);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
	curl_setopt($ch, CURLOPT_BINARYTRANSFER,1);
	$image = curl_exec($ch);
	curl_close($ch);

	var a = {name: "a", fun: function () { return this; }};
	console.log(a.fun());
	//=> {name "a", fun: ...}

	var bFunc = function () { return this };
	var b = {name: "b", fun: bFunc};

	console.log(b.fun());
	//=> {name: "b", fun: ...}
	// not some global object

	var ifs = function (args, i) {
	var i = i \|\| 0;
	if (i == args.length - 1) { return args[i] }
	else if (i > args.length - 1) { return undefined }

	if (args[i]) { return args[i + 1] }
	else { return ifs(args, i + 2) }
	}

Drew LeSueur drewlesueur

How to Generate the Y-Combinator in CoffeeScript

Problem

this is a title

foo

	function scale(x, realMin, realMax, scaledMin, scaledMax) {
	var realDiff = realMax - realMin
	var scaledDiff = scaledMax - scaledMin
	var xOffset = x - realMin
	var ratio = xOffset / realDiff
	var appliedValue = ratio * scaledDiff
	var ret = scaledMin + appliedValue
	return ret
	}

	<!doctype html>
	<html>
	<head>
	</head>
	<body>

	<div style="height: 400px; border: 1px solid green; width: 300px; display: flex; flex-flow: column nowrap; ">
	<div style="padding: 20px; background-color: orange; ">I am a header</div>

	<div style="flex: 1 1 auto; display: flex; flex-flow: column nowrap; overflow: auto;">