run plugins optionally

lib/peg.js

@@ -29,16 +29,19 @@ const peg = {
 
         options = typeof options !== "undefined" ? options : {};
 
-        const plugins = "plugins" in options ? options.plugins : [];
         const session = new compiler.Session( {
             passes: util.convertPasses( compiler.passes )
         } );
 
-        plugins.forEach( p => {
+        if ( Array.isArray( options.plugins ) )
 
-            p.use( session, options );
+            options.plugins.forEach( p => {
 
-        } );
+                if ( typeof p.use !== "function" ) return;
+
+                p.use( session, options );
+
+            } );
 
         return compiler.compile(
             session.parse( grammar, options.parser || {} ),