Compile-time determinations” are exactly that: they occur when the source-code is compiled and are forever-after fixed into the resulting executable.

You're ignoring the flexibility of what constistutes "compile-time" in dynamic languages like Perl.

See also the subthread starting at Re: Runtime introspection: What good is it? which discusses how compiled to binary (static) languages achieve dynamic language-like flexibility through the use of parsers without giving up their compile-time type correctness, or succumbing to building a run-time eval capability.

I must admit, I'm surprised to find you, as an "planning is paramount" advocate, coming down on the side of making ad-hoc codepath descisions at run-time :)