$ perl
use Lexical::Alias 'alias_r';

my $s;
alias_r \"I am immutable", \$s;

$s = "fie!";
^D
Modification of a read-only value attempted at - line 6.
$

##</code><code>##

[...]
my $s;
{
  local $tmp;
  *tmp=\"I am immutable";
  alias_r \$tmp, \$s;
}
[...]