You know, this response is itself enough to make me agree that qr//e is a bad idea. Thanks for taking the time to beat it into my thick skull. I now think that true eval is overkill.

(Although, to be fair, the issues you bring up are already solved for the replacement text in s///e, are they not?)

Having said that, can you think of a syntax that would express my intent of applying qr to a value that is generated some way other than double-quote or regex interpolated? My original examples, for reference:

  my @days    = qw( Sun Mon Tue Wed Thu Fri Sat );
  my $days_re = do { my $tmp = join '|', @days; qr/$tmp/; }
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Using some of the other ideas that have cropped up, I could perhaps just do this:

  sub compile_regex ( $ ) { qr/$_[0]/; }

  my $days_re = compile_regex join '|', @days;
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Although I still like the cuteness factor of doing it this way:

  my $days_re = qr->( join '|', @days );
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Too bad that breaks valid code.