How do I determine the number of arguments a function takes in Haxe?

How can I determine the number of arguments a function takes in Haxe?

I've looked at the Reflect and Type APIs without success. In AS3 and JavaScript, you can do Function#length. Similar reflective abilities are available for most, if not all, of the other Haxe targets.

Given Haxe's great type system, I'm surprised I haven't been able to deduce how to do this.