refactor filters and corresponding tests

src/lexical.js

@@ -1,14 +1,16 @@
 // quote related
 var singleQuoted = /'[^']*'/;
 var doubleQuoted = /"[^"]*"/;
-var quoteBalanced = new RegExp(`(?:${singleQuoted.source}|${doubleQuoted.source}|[^'"])*`);
+var quoted = new RegExp(`${singleQuoted.source}|${doubleQuoted.source}`);
+var quoteBalanced = new RegExp(`(?:${quoted.source}|[^'"])*`);
 
-var number = /(?:-?\d+\.?\d*|\.?\d+)/;
+// values
+var integer = /-?\d+/;
+var number = /-?\d+\.?\d*|\.?\d+/;
 var bool = /true|false/;
-var identifier = /[a-zA-Z_$][a-zA-Z_$0-9]*/;
-var subscript = /\[\d+\]/;
+var identifier = /[\w-]+/;
+var subscript = new RegExp(`\\[(?:${quoted.source}|[\\w-\\.]+)\\]`);
 
-var quoted = new RegExp(`(?:${singleQuoted.source}|${doubleQuoted.source})`);
 var literal = new RegExp(`(?:${quoted.source}|${bool.source}|${number.source})`);
 var variable = new RegExp(`${identifier.source}(?:\\.${identifier.source}|${subscript.source})*`);
 
@@ -69,7 +71,7 @@ function parseLiteral(str) {
 }
 
 module.exports = {
-    quoted, number, bool, literal, filter,
+    quoted, number, bool, literal, filter, integer,
     hash, hashCapture,
     range, rangeCapture, 
     identifier, value, quoteBalanced, operators,

src/util/underscore.js

@@ -1,5 +1,29 @@
-function isString(value){
+/*
+ * Checks if value is classified as a String primitive or object.
+ * @param {any} value The value to check.
+ * @return {Boolean} Returns true if value is a string, else false.
+ */
+function isString(value) {
     return value instanceof String || typeof value === 'string';
 }
 
+/*
+ * Iterates over own enumerable string keyed properties of an object and invokes iteratee for each property. 
+ * The iteratee is invoked with three arguments: (value, key, object). 
+ * Iteratee functions may exit iteration early by explicitly returning false.
+ * @param {Object} object The object to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @return {Object} Returs object.
+ */
+function forOwn(object, iteratee) {
+    object = object || {};
+    for (var k in object) {
+        if (object.hasOwnProperty(k)) {
+            if (iteratee(object[k], k, object) === false) break;
+        }
+    }
+    return object;
+}
+
 exports.isString = isString;
+exports.forOwn = forOwn;