[twic]

While ideal from a theoretical perspective, as a practical matter, can you imagine renaming a 10 GB file by first creating a copy of it, and then deleting the old version?!?

That kind of inefficiency is not practical for most real world programs!

To solve this problem, we can write an optimizing interpreter, which is a special kind of interpreter that can detect patterns and substitute them with semantically equivalent but faster alternatives.

But why?