use warnings;
use strict;
use Test::More;
sub testre;

# The "normal" solution
my $re = join '|', map {quotemeta} qw/a . | %/;
testre  qr/$re/i ;

# The "hacked" solution
testre  qr{@{[ join '|', map {quotemeta} qw/a . | %/ ]}}i ;

# Wouldn't this be a bit nicer?
#testre  qr{ join '|', map {quotemeta} qw/a . | %/ }ei ;

# ### Update ###

# Thanks to LanX
sub qre (&;$) {
    my $re = shift->();
    eval 'qr/$re/'.(shift//'') || die $@
}
testre  qre{ join '|', map {quotemeta} qw/a . | %/ }'i' ;

# Thanks to Haarg
testre  map qr/$_/i, join '|', map {quotemeta} qw/a . | %/ ;

# Thanks to vr
testre  qr{(??{ join '|', map {quotemeta} qw/a . | %/ })}i ;

done_testing;

sub testre {
    my $re = shift;
    diag explain $re;
    is ref $re, 'Regexp';
    like $_, $re for qw/A . | %/;
    unlike 'bcd', $re;
}