I want use coffeescript function syntax to write python lambda expression so I modified the Grammar file.

```

atom: ('(' [yield_expr|testlist_comp|vararglist] ')' |

       '[' [testlist_comp] ']' |

       '{' [dictorsetmaker] '}' |

       NAME | NUMBER | STRING+ | '...' | 'None' | 'True' | 'False')

trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME | '->' text

```

but when I write

```

(x,y=1)->x+y

```

the parser doesn't go into vararglist.