Previous in list filter.

core/modules/filters/previous.js

@@ -0,0 +1,43 @@
+/*\
+title: $:/core/modules/filters/previous.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator returning the tiddler whose title occurs immediately prior in the list supplied in the operand tiddler
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.previous = function(source,operator,options) {
+	var results = [],
+		list = options.wiki.getTiddlerList(operator.operand);
+
+	function checkTiddler(title) {
+		var match = list.indexOf(title);
+		// decrement match and then test if result is in range
+		match--;
+		if( match >= 0 ) {
+			results.push(list[match]);
+		}
+	}
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		$tw.utils.each(source,function(title) {
+			checkTiddler(title);
+		});
+	} else {
+		$tw.utils.each(source,function(element,title) {
+			checkTiddler(title);
+		});
+	}
+	return results;
+};
+
+})();