Precedence in parsing types

It looks to me like this should parse, but it doesn't:

var x: number | (string)=>void;

It works with added parens:

var x: number | ((string)=>void);

But if the parser is not too hacky, then maybe it's easy to make the first work?

(FWIW, I ran into this in a rest argument, where it would be nice to avoid the extra parens in

function foo(...xs: (number | ()=>void)[]): void { }

)