my %vars; # something to hold all your variables in

sub set_var {
	my ($name, $value) = @_;

	$vars{$name} = $value;
}

sub get_var {
	my $name = shift;
	my $var = $vars{$name};
	return ref $var eq 'CODE' ? $var->() : $var;
}

set_var(foo => "hello");
set_var(x => sub { return get_var('foo') . get_var('y') });
set_var(y => 'world');

print get_var('x'), "\n";