Reliable way to detect a login shell?

[Clint Olsen <olsenc@xxxxxxxxxxxxxxxx>]

Is there a way to tell (checking switches/arguments) that a particular
shell is a login shell?  I'd like to be able to do this in my .zshenv to
set some options.

For example:

if [ i'm a login shell ]; then
  set -o ignoreeof
fi

Thanks,

-Clint