You can use a reference-dereference trick, or the experimental postponed regular subexpression. 
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };

{   package Re;
    sub re { qr/perl/i }
}

say 'perl Perl PERL' =~ /${ \Re::re() }/g;
say 'perl Perl PERL' =~ /(??{ Re::re() })/g;

[download]
($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,

[download]

In reply to Re: Use function as a regex by choroba
in thread Use function as a regex by stevieb

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