Only the programmed end result in code would be legally binding. Lawmakers would have a big interst in making sure the code is correct and provide incentives/change procedures accordingly.

The inmates in this article would be released immediately after the code-law is implemented; you could apply new tax laws (i.e. as a config file) to your accounting software.

Why maintain an obfuscated legal text when you need it in software anyway?

The legal text is the specification. What you're suggesting is the equivalent of the classic "the spec is whatever the implementation does", and would erase the distinction between correct, incorrect, and undefined behaviour.

In other words: “it’s not a bug. it’s a feature!”