helpers/-for-of.js
function(helperOptions) {
	// lookup

	// TODO: remove in prod
	// make sure we got called with the right stuff
	if(helperOptions.exprData.argExprs.length !== 1) {
		throw new Error("for(of) broken syntax");
	}

	// TODO: check if an instance of helper;

	var helperExpr = helperOptions.exprData.argExprs[0].expr;
	var variableName, valueLookup, valueObservable;
	if(helperExpr instanceof expression.Lookup) {

		valueObservable = helperExpr.value(helperOptions.scope);

	} else if(helperExpr instanceof expression.Helper) {
		// TODO: remove in prod
		var inLookup = helperExpr.argExprs[0];
		if(inLookup.key !== "of") {
			throw new Error("for(of) broken syntax");
		}
		variableName = helperExpr.methodExpr.key;
		valueLookup = helperExpr.argExprs[1];
		valueObservable = valueLookup.value(helperOptions.scope);
	}

	var items =  valueObservable;

	var args = [].slice.call(arguments),
		options = args.pop(),
		resolved = bindAndRead(items);

	if(resolved && !canReflect.isListLike(resolved)) {
		return forOfObject(resolved,variableName, helperOptions);
	}
	if(options.stringOnly) {
		var parts = [];
		canReflect.eachIndex(resolved, function(value, index){
			var variableScope = {};
			if(variableName !== undefined){
				variableScope[variableName] = value;
			}
			parts.push(
				helperOptions.fn( options.scope
					.add({ index: index }, { special: true })
					.addLetContext(variableScope) )
			);
		});
		return parts.join("");
	} else {
		// Tells that a helper has been called, this function should be returned through
		// checking its value.
		options.metadata.rendered = true;
		return function(el){
			// make a child nodeList inside the can.view.live.html nodeList
			// so that if the html is re
			var nodeList = [el];
			nodeList.expression = "live.list";
			nodeLists.register(nodeList, null, options.nodeList, true);
			// runs nest replacements
			nodeLists.update(options.nodeList, [el]);


			var cb = function (item, index, parentNodeList) {
				var variableScope = {};
				if(variableName !== undefined){
					variableScope[variableName] = item;
				}
				return options.fn(
					options.scope
					.add({ index: index }, { special: true })
					.addLetContext(variableScope),
				options.options,
				parentNodeList
				);
			};

			live.list(el, items, cb, options.context, el.parentNode, nodeList, function(list, parentNodeList){
				return options.inverse(options.scope, options.options, parentNodeList);
			});
		};
	}
}
function(helperOptions) {
	// lookup

	// TODO: remove in prod
	// make sure we got called with the right stuff
	if(helperOptions.exprData.argExprs.length !== 1) {
		throw new Error("for(of) broken syntax");
	}

	// TODO: check if an instance of helper;

	var helperExpr = helperOptions.exprData.argExprs[0].expr;
	var variableName, valueLookup, valueObservable;
	if(helperExpr instanceof expression.Lookup) {

		valueObservable = helperExpr.value(helperOptions.scope);

	} else if(helperExpr instanceof expression.Helper) {
		// TODO: remove in prod
		var inLookup = helperExpr.argExprs[0];
		if(inLookup.key !== "of") {
			throw new Error("for(of) broken syntax");
		}
		variableName = helperExpr.methodExpr.key;
		valueLookup = helperExpr.argExprs[1];
		valueObservable = valueLookup.value(helperOptions.scope);
	}

	var items =  valueObservable;

	var args = [].slice.call(arguments),
		options = args.pop(),
		resolved = bindAndRead(items);

	if(resolved && !canReflect.isListLike(resolved)) {
		return forOfObject(resolved,variableName, helperOptions);
	}
	if(options.stringOnly) {
		var parts = [];
		canReflect.eachIndex(resolved, function(value, index){
			var variableScope = {};
			if(variableName !== undefined){
				variableScope[variableName] = value;
			}
			parts.push(
				helperOptions.fn( options.scope
					.add({ index: index }, { special: true })
					.addLetContext(variableScope) )
			);
		});
		return parts.join("");
	} else {
		// Tells that a helper has been called, this function should be returned through
		// checking its value.
		options.metadata.rendered = true;
		return function(el){
			// make a child nodeList inside the can.view.live.html nodeList
			// so that if the html is re
			var nodeList = [el];
			nodeList.expression = "live.list";
			nodeLists.register(nodeList, null, options.nodeList, true);
			// runs nest replacements
			nodeLists.update(options.nodeList, [el]);


			var cb = function (item, index, parentNodeList) {
				var variableScope = {};
				if(variableName !== undefined){
					variableScope[variableName] = item;
				}
				return options.fn(
					options.scope
					.add({ index: index }, { special: true })
					.addLetContext(variableScope),
				options.options,
				parentNodeList
				);
			};

			live.list(el, items, cb, options.context, el.parentNode, nodeList, function(list, parentNodeList){
				return options.inverse(options.scope, options.options, parentNodeList);
			});
		};
	}
}
this is called with the ast ... we are going to use that to our advantage.