"Perl 6 exposes signatures as objects, and allows you introspect that parameter list"

FYI, the Kavorka signature syntax and introspection API shown in my answer is very much inspired by Perl 6.

Your example:

$ perl6-m -e 'sub f($x, $a, $b) { }; say &f.signature.params[1].name'
$a
[download]

... translates to:

perl -MKavorka -E'fun f($x, $a, $b){ }; say Kavorka->info(\&f)->signat
+ure->params->[1]->name'
[download]

My policy was generally, "if in doubt, do things like Perl 6".

I do really need to experiment with blessing coderefs, allowing things like: (\&f)->signature to "just work".