diff --git a/README.md b/README.md
index 28ce480..33d03af 100644
--- a/README.md
+++ b/README.md
@@ -68,7 +68,7 @@ Values | Description
 --- | ---
 43, -1.234 | Numbers
 "hello" | String
-foo, a.b.c | External data variable defined by application (may be numbers or strings)
+foo, a.b.c, 'foo-bar' | External data variable defined by application (may be numbers or strings)
 
 Numeric arithmetic | Description
 --- | ---
@@ -86,6 +86,7 @@ x < y | Less than
 x <= y | Less than or equal to
 x > y | Greater than
 x >= y | Greater than or equal to
+x ~= y | Regular expression match
 x in (a, b, c) | Equivalent to (x == a or x == b or x == c)
 x not in (a, b, c) | Equivalent to (x != a and x != b and x != c)
 
diff --git a/filtrex.js b/filtrex.js
index 6b47d93..8846331 100644
--- a/filtrex.js
+++ b/filtrex.js
@@ -89,6 +89,7 @@ function filtrexParser() {
                 ['\\,', 'return ",";'],
                 ['==', 'return "==";'],
                 ['\\!=', 'return "!=";'],
+                ['\\~=', 'return "~=";'],
                 ['>=', 'return ">=";'],
                 ['<=', 'return "<=";'],
                 ['<', 'return "<";'],
@@ -103,6 +104,7 @@ function filtrexParser() {
                 ['\\s+',  ''], // skip whitespace
                 ['[0-9]+(?:\\.[0-9]+)?\\b', 'return "NUMBER";'], // 212.321
                 ['[a-zA-Z][\\.a-zA-Z0-9_]*', 'return "SYMBOL";'], // some.Symbol22
+                ['\'(?:[^\'])*\'', 'yytext = yytext.substr(1, yyleng-2); return "SYMBOL";'], // 'some-symbol'
                 ['"(?:[^"])*"', 'yytext = yytext.substr(1, yyleng-2); return "STRING";'], // "foo"
 
                 // End
@@ -119,7 +121,7 @@ function filtrexParser() {
             ['left', 'or'],
             ['left', 'and'],
             ['left', 'in'],
-            ['left', '==', '!='],
+            ['left', '==', '!=', '~='],
             ['left', '<', '<=', '>', '>='],
             ['left', '+', '-'],
             ['left', '*', '/', '%'],
@@ -145,6 +147,7 @@ function filtrexParser() {
                 ['not e'  , code(['Number(!', 2, ')'])],
                 ['e == e' , code(['Number(', 1, '==', 3, ')'])],
                 ['e != e' , code(['Number(', 1, '!=', 3, ')'])],
+                ['e ~= e' , code(['RegExp(', 3, ').test(', 1, ')'])],
                 ['e < e'  , code(['Number(', 1, '<' , 3, ')'])],
                 ['e <= e' , code(['Number(', 1, '<=', 3, ')'])],
                 ['e > e'  , code(['Number(', 1, '> ', 3, ')'])],
diff --git a/src/filtrex.js b/src/filtrex.js
index b8acb6f..927fdc1 100644
--- a/src/filtrex.js
+++ b/src/filtrex.js
@@ -46,9 +46,12 @@ function compileExpression(expression, extraFunctions /* optional */) {
     tree.forEach(toJs);
     js.push(';');
 
-    var func = new Function('functions', 'data', js.join(''));
+    function unknown(funcName) {
+        throw 'Unknown function: ' + funcName + '()';
+    }
+    var func = new Function('functions', 'data', 'unknown', js.join(''));
     return function(data) {
-        return func(functions, data);
+        return func(functions, data, unknown);
     };
 }
 
@@ -86,6 +89,7 @@ function filtrexParser() {
                 ['\\,', 'return ",";'],
                 ['==', 'return "==";'],
                 ['\\!=', 'return "!=";'],
+                ['\\~=', 'return "~=";'],
                 ['>=', 'return ">=";'],
                 ['<=', 'return "<=";'],
                 ['<', 'return "<";'],
@@ -100,6 +104,7 @@ function filtrexParser() {
                 ['\\s+',  ''], // skip whitespace
                 ['[0-9]+(?:\\.[0-9]+)?\\b', 'return "NUMBER";'], // 212.321
                 ['[a-zA-Z][\\.a-zA-Z0-9_]*', 'return "SYMBOL";'], // some.Symbol22
+                ['\'(?:[^\'])*\'', 'yytext = yytext.substr(1, yyleng-2); return "SYMBOL";'], // 'some-symbol'
                 ['"(?:[^"])*"', 'yytext = yytext.substr(1, yyleng-2); return "STRING";'], // "foo"
 
                 // End
@@ -116,7 +121,7 @@ function filtrexParser() {
             ['left', 'or'],
             ['left', 'and'],
             ['left', 'in'],
-            ['left', '==', '!='],
+            ['left', '==', '!=', '~='],
             ['left', '<', '<=', '>', '>='],
             ['left', '+', '-'],
             ['left', '*', '/', '%'],
@@ -142,6 +147,7 @@ function filtrexParser() {
                 ['not e'  , code(['Number(!', 2, ')'])],
                 ['e == e' , code(['Number(', 1, '==', 3, ')'])],
                 ['e != e' , code(['Number(', 1, '!=', 3, ')'])],
+                ['e ~= e' , code(['RegExp(', 3, ').test(', 1, ')'])],
                 ['e < e'  , code(['Number(', 1, '<' , 3, ')'])],
                 ['e <= e' , code(['Number(', 1, '<=', 3, ')'])],
                 ['e > e'  , code(['Number(', 1, '> ', 3, ')'])],
@@ -151,7 +157,7 @@ function filtrexParser() {
                 ['NUMBER' , code([1])],
                 ['STRING' , code(['"', 1, '"'])],
                 ['SYMBOL' , code(['data["', 1, '"]'])],
-                ['SYMBOL ( argsList )', code(['functions.', 1, '(', 3, ')'])],
+                ['SYMBOL ( argsList )', code(['(functions.hasOwnProperty("', 1, '") ? functions.', 1, '(', 3, ') : unknown("', 1, '"))'])],
                 ['e in ( inSet )', code([1, ' in (function(o) { ', 4, 'return o; })({})'])],
                 ['e not in ( inSet )', code(['!(', 1, ' in (function(o) { ', 5, 'return o; })({}))'])],
             ],
diff --git a/test/filtrex-test.html b/test/filtrex-test.html
index a73766f..eb1151d 100644
--- a/test/filtrex-test.html
+++ b/test/filtrex-test.html
@@ -104,6 +104,11 @@
         eq(1, compileExpression('foo not in ("aa", "bb")')({foo:'cc'}));
     },
 
+    'regexp test': function() {
+        eq(1, compileExpression('foo ~= "^[hH]ello"')({foo:'hello'}));
+        eq(0, compileExpression('foo ~= "^[hH]ello"')({foo:'bye'}));
+    },
+
     'a ? b : c': function() {
         eq(4, compileExpression('1 > 2 ? 3 : 4')());
         eq(3, compileExpression('1 < 2 ? 3 : 4')());
@@ -120,6 +125,11 @@
         eq(123, compileExpression('order.gooandstuff')({'order.gooandstuff': 123}));
     },
 
+    'quoted symbols': function() {
+        eq(123, compileExpression('\'hello-world-foo\'')({'hello-world-foo': 123}));
+        eq(123, compileExpression('\'order+goo*and#stuff\'')({'order+goo*and#stuff': 123}));
+    },
+
     'custom functions': function() {
         function triple(x) { return x * 3; };
         eq(21, compileExpression('triple(v)', {triple:triple})({v:7}));