Am I missing something about this `unless` keyword? From what it looks like, it's just syntactic sugar for `if not`, and it makes much more sense… (unless

Am I missing something about this `unless` keyword? From what it looks like, it's just syntactic sugar for `if not`, and it makes much more sense… (unless (string= a b) (fail)) ;; much more readable than (when (string/= a b) (fail))