Basically, you wrote it so BASIC_COMMENT is PERL_CODE while BASIC_CODE is PERL_COMMENT... Both parts are distinct: remove the Perl code and the BASIC works pretty well.

This is the first step into polyglots, but don't stop here.

Next, you can try using the variable q$ in BASIC, which will allow you to hide a little BASIC into a Perl quoted-string... Then you begin to intermix the two languages. That is where the real fun part begins.

Until you reach a point where every part of the code is essential. When you're stuck with your code, and it's just... beautyful. Like a work by M. C. Escher.

Of all aspects of writing polyglots, this is the best, ever... (soooorry, couldn't help)