it dosn't eval every statement to see if they are good in reality.

First of all, it can't. For example, how could it run a statment before its containing block has finished compiling?

Secondly, it's impossible to detect most programming errors. For a system to check for errors, it would have to know what you are trying to do, but if it knew what you wanted to do, there would be no need to write a program to tell it what to do. It is possible for the system to look for patterns that usually result in errors. When Perl detects such a pattern, it issues a warning. Some at compile-time, some at run-time.

Finally, how does your post relate to its parent post?