All the regex examples you've shown are deterministic, so to speak, but how would you expand, for example, a quantifier such as * or +? a+ could be anything like "a", "aa", "aaa", and so on. How would you express anchors? Zero-width assertions? Greedy and non-greedy quantifiers? And so on.

Or you would have to explain how you want them to be translated. Or perhaps I missed what you're looking for?