Code that will only execute once
Vigil
Finally a usecase for Vigil!
def main():
  raise Exception()

Excerpt from the &quot;language specification&quot;:

It goes without saying that any function that throws an exception which isn't caught is wrong and must be punished.
...
If an oath is broken, the offending function [...] will be duly punished.
How?
Simple: it will be deleted from your source code.
The only way to ensure your program meets its requirements to absolutely forbid code that fails to do so. With Vigil, it will do this for you automatically.

There are other ways to do this, because Vigil provides the keywords implore and swear which are basically oaths to adhere to certain pre- and post-conditions:
def main():
  swear 0 &gt; 1