C:\Documents and Settings\Owner\Desktop>perl -MO=Deparse,  consttest.pl & perl c
onsttest.pl
BEGIN { $^W = 1; }
sub BEGIN {
    package mod;
    $VERSION = 1;
}
sub BEGIN {
    if (scalar %mod:: and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    if (haveMod) {
        return 'goodMod';
    }
    else {
        return 'badMod';
    }
}
print checkMod;
consttest.pl syntax OK
goodMod
C:\Documents and Settings\Owner\Desktop>