BEGIN {
    my $level = $ENV{'FOO_DEBUG'} || 0;
    eval "*Foo::DEBUG = sub () {$1}" if $level =~ m#^(\d+)$#s;
} #BEGIN

if (Foo::DEBUG) {
    print "We're debugging\n";
}

##</code><code>##

sub BEGIN {
    my $level = $ENV{'FOO_DEBUG'} || 0;
    eval "*Foo::DEBUG = sub () {$1}" if $level =~ /^(\d+)$/s;
}
'???';

##</code><code>##

sub BEGIN {
    my $level = $ENV{'FOO_DEBUG'} || 0;
    eval "*Foo::DEBUG = sub () {$1}" if $level =~ /^(\d+)$/s;
}
do {
    print "We're debugging\n"
};