I just realized that this may be quite easy to implement using existing features. Where 'this' is to run 'eval' in order to check for syntax errors while preventing any code from being run, even if a form of 'BEGIN' is used in the code.

I believe that there are ways to hook Perl's "run loop". So the steps would be:

1. fork to get a new Perl interpreter instance (will work even on Windows)
2. In the child instance, hook the "run loop"
3. Call "eval $code"
4. The run loop hook would allow Perl opnodes to execute until the 'eval' op hit
5. If any other ops try to run after that, die
6. CORE::exit to destroy the Perl interpreter that might have had some functions defined that we don't want to call by accident

Unfortunately, I don't know how you hook Perl's run-loop. And there might be complications to overcome when getting into the details of making this work.

But I can see real value in such a feature.

Disabling the running of code may be as simple as just defining "sub DB::sub" and "sub DB::DB" (you probably need to put your code that calls eval() into 'package DB' so it wouldn't be subject to the debugging hooks). But you can also look at what Enbugger does to enable debugging or what Devel::NYTProf does to profile opcodes.