And then you keep adding things and adding things and you've created your own language (c.f. PHP :). If you want a more full featured language you've got two options:

• write your own interpreter (using something like Parse::RecDescent or byacc)
• let your users just write perl and have a wrapper hide details like use MyLanguageModule qw( blah blah )

If you've got users that can handle it I'd go for the later as it's less work for you and they don't have to learn yet another language.