diff --git a/dist/carto.js b/dist/carto.js
index 68fc973..bac285c 100644
--- a/dist/carto.js
+++ b/dist/carto.js
@@ -1,4 +1,11 @@
 
+var assert = {
+  ok: function(value, message) {
+    message = message || '';
+    if(!value) throw new Error("assertion failed", message);
+  }
+}
+
 var carto_initialize = function(carto, uri, callback) {
   callback();
 };
@@ -2936,9 +2943,7 @@ tree.Comment.prototype = {
 
 })(require('../tree'));
 (function(tree) {
-var assert = require('assert') || {
-    ok: function() { }
-};
+var assert = require('assert');
 
 tree.Definition = function Definition(selector, rules) {
     this.elements = selector.elements;
@@ -3842,14 +3847,19 @@ tree.Quoted.prototype = {
 
 
 var _ = require('underscore');
-var mapnik_reference = require('mapnik-reference');
+var reference = require('mapnik-reference');
 
 tree.Reference = {
-    data: mapnik_reference.version.latest
+    data: reference.version.latest
+};
+
+tree.Reference.setReference = function(ref, version) {
+    reference = ref;
+    tree.Reference.setVersion(version || 'latest');
 };
 
 tree.Reference.setVersion = function(version) {
-    tree.Reference.data = mapnik_reference.version[version];
+    tree.Reference.data = reference.version[version];
 };
 
 tree.Reference.required_prop_list_cache = {};
@@ -4872,7 +4882,8 @@ CartoCSS.renderers['canvas-2d'] = {
     'line-opacity': 'globalAlpha',
     // polygon
     'polygon-fill': 'fillStyle',
-    'polygon-opacity': 'globalAlpha'
+    'polygon-opacity': 'globalAlpha',
+    'comp-op': 'comp-op'
   },
 
   transform: function(src) {
@@ -4959,6 +4970,9 @@ CartoCSS.prototype = {
 
   setStyle: function(style) {
     var layers = this.parse(style);
+    if(!layers) {
+      throw new Error(this.parse_env.errors);
+    }
     this.layers = layers.map(function(shader) {
         return new CartoCSS.Layer(shader);
     });
@@ -4970,6 +4984,7 @@ CartoCSS.prototype = {
 
   _createFn: function(ops) {
     var body = ops.join('\n');
+    console.log(body);
     return Function("data","ctx", "var _value = null; " +  body + "; return _value; ");
   },
 
diff --git a/makefile b/makefile
index 4a64d24..fb75236 100644
--- a/makefile
+++ b/makefile
@@ -8,6 +8,8 @@ uglify = ./node_modules/.bin/uglify
 
 JS_CLIENT_FILES=browser/*.js lib/carto/parser.js lib/carto/tree.js lib/carto/tree/*.js lib/carto/functions.js lib/carto/renderer_js.js
 
+all: dist
+
 lint:
 	./node_modules/.bin/jshint lib/carto/*.js lib/carto/tree/*.js
 
@@ -25,8 +27,9 @@ doc:
 	$(docco) lib/carto/*.js lib/carto/tree/*.js
 
 dist/carto.js: $(JS_CLIENT_FILES)
-	cat browser/*.js lib/carto/parser.js lib/carto/tree.js lib/carto/tree/*.js lib/carto/functions.js lib/carto/renderer_js.js > dist/carto.js
+	cat $(JS_CLIENT_FILES) > dist/carto.js
 
 dist: dist/carto.js
 
+
 .PHONY: test