“Why, yes,” you reply, “one can say in a regex”: 

$ perl -E '/(?{ say "See?" })/'
See?

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“But,” I reply, “what if you want to interpolate a pattern?” 
$ perl -E 'use re "eval"; my $a = qr//; /(?{ say("See?") })$a/'
Undefined subroutine &main::say called at (re_eval 1) line 1.

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Thoughts?

UPDATE: ambrus suggested in the CB to remind the compiler that I want to use 5.010, and that works: 

$ perl -E 'use re "eval"; my $a = qr//; /(?{ use 5.010; say "See?" })$
+a/'
See?

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which solves my problem, but seems strange. Why should the presence or absence of an empty regex require me to add an apparently superfluous use?
UPDATE: ambrus answered that, too. It's because the interpolated regex changes the big regex from a constant that can be compiled at compile time, to something not known to be constant that must be compiled at run time. Ah, well. I was too eager to post. :-)

In reply to Can't say in a regex? by JadeNB

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