I also find the syntax a bit odd, including the return types. Plus the brackets for multiple arguments that appear in the interface but not in the implementation are inexplicably inconsistent. (Update: See below.)

I would also be very curious how well eero adapts to pure C code. Many of Apple's performance-critical APIs are C, as our many third party libraries. So being able to effortless invoke C within Objective-C is essential.

eero's design seems to neglect this. For one, goto is outright banned, eliminating a rather effective tool for elegant C based error handling. (http://stackoverflow.com/questions/788903/valid-use-of-goto-..., but please let's avoid a long tangent on the proper use of goto)

Update: My mistake, the brackets apparently define an argument as optional, which might be a convenient shortcut in some cases.