error management, an exception is thrown when there is a parse error

lib/carto/renderer_js.js

@@ -131,7 +131,8 @@ CartoCSS.renderers['canvas-2d'] = {
     'line-opacity': 'globalAlpha',
     // polygon
     'polygon-fill': 'fillStyle',
-    'polygon-opacity': 'globalAlpha'
+    'polygon-opacity': 'globalAlpha',
+    'comp-op': 'comp-op'
   },
 
   transform: function(src) {
@@ -218,6 +219,9 @@ 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);
     });
@@ -229,6 +233,7 @@ CartoCSS.prototype = {
 
   _createFn: function(ops) {
     var body = ops.join('\n');
+    console.log(body);
     return Function("data","ctx", "var _value = null; " +  body + "; return _value; ");
   },