> perl -w
use strict;
BEGIN {
    my $n= 5;
    while( calldepth < $n ) {
        warn $n--;
    }
}
Argument "calldepth" isn't numeric in numeric lt (<) at - line 4.
5 at - line 5.
4 at - line 5.
3 at - line 5.
2 at - line 5.
1 at - line 5.
my $x
= 5;
BEGIN {
    warn "interesting"
}
Bareword "calldepth" not allowed while "strict subs" in use at - line 4.
BEGIN not safe after errors--compilation aborted at - line 12.