May I see a POC with prototypes for that?

Because this

> sub catchif ($&;@)

will require a sub before and a comma after the block.

You are right. It would have been too easy. ;-) perlsub is quite clear:

An & requires an anonymous subroutine, which, if passed as the first argument, does not require the sub keyword or a subsequent comma.

I did not remember the "first argument" exception and assumed an anonymous sub would work in any position.

Alexander