update custom types example

do not execute console.log when module is required
and exports are used

examples/custom_types.js

@@ -79,23 +79,23 @@ var SpaceYamlType = new yaml.Type('!space', {
 
 var SPACE_SCHEMA = yaml.Schema.create([ SpaceYamlType, PointYamlType ]);
 
-
-// And read a document using that schema.
-
-fs.readFile(path.join(__dirname, 'custom_types.yml'), 'utf8', function (error, data) {
-  var loaded;
-
-  if (!error) {
-    loaded = yaml.load(data, { schema: SPACE_SCHEMA });
-    console.log(util.inspect(loaded, false, 20, true));
-  } else {
-    console.error(error.stack || error.message || String(error));
-  }
-});
-
+// do not execute the following if file is required (http://stackoverflow.com/a/6398335)
+if (require.main === module) {
+
+  // And read a document using that schema.
+  fs.readFile(path.join(__dirname, 'custom_types.yml'), 'utf8', function (error, data) {
+    var loaded;
+
+    if (!error) {
+      loaded = yaml.load(data, { schema: SPACE_SCHEMA });
+      console.log(util.inspect(loaded, false, 20, true));
+    } else {
+      console.error(error.stack || error.message || String(error));
+    }
+  });
+}
 
 // There are some exports to play with this example interactively.
-
 module.exports.Point         = Point;
 module.exports.Space         = Space;
 module.exports.PointYamlType = PointYamlType;