Clearly a fluid API can not return a 2+ tuple as its results so the error issue you note is a non-issue. The clean way to deal with errors in fluid APIs is to

Clearly a fluid API can not return a 2+ tuple as its results so the error issue you note is a non-issue. The clean way to deal with errors in fluid APIs is to have a terminal .init() that returns an error (which can also specifically note which options are "illegal", etc.)