use v5.12;
use warnings;
use re 'eval';

my $re = templ2regex("Mississippi");

for my $inp (qw/Mississippi Mossossoppo Miiiiiiippi/) {
    if ( my @matches = ( $inp =~ /$re/ ) ) {
        say "Match: $inp re: $re";
    }
}

# Mississippi -> (.)(.)(.)\3\2\3\3\2(.)\4\2
sub templ2regex {
    my ($template) = @_;

    my ( $re, %grp, $cnt );

    # not sure if that's better readable than before
    $re =                                          
        join "",
        map {
            $grp{$_} //
              do {
                  $grp{$_} = "\\" . ++$cnt;
                  "(.)"
                 }
        }
        split //, $template;

    $re .= '(?(?{not is_uniq( @{^CAPTURE} ) }) (*FAIL) )';
    return $re;
}

# @_ elements all distinct?
sub is_uniq {
    my %uniq;
    @uniq{@_} = ();
    return @_ == keys %uniq;
}