Lexical vars in a closure

gistfile1.txt

#!/usr/bin/env perl

use warnings;
use strict;

{
	my %hsh = map { ($_ => 1) } qw( some costy hashmap here );
	sub has {
		return $hsh{$_[0]};
	}
};

print has('costy'), "\n";
print has('hash'), "\n";

Subs are "global", i.e. kept in package symbol table, which you can manipulate during runtime, e.g.

sub a_gen {
    return \&a;
}

sub a { 'outer' };

say a, a_gen->(); # says outerouter

{
    no warnings 'redefine';                                                     
    local *a = sub { 'inner' };

    say a(), a_gen->(); # says innerinner
}

say a, a_gen->(); # says outerouter