Plugins: How to determine ghc vs ghci

I'm working on a plugin, and would like to be able to tell if it's GHC or GHCi that's running. I tried: df <- getDynFlags let isGHCi = ghcMode df == CompManager Alas, while that correctly tells apart "ghci" from "ghc -c", it also returns True when ghc is called without the "-c" argument. Is there a better/more robust way of figuring out whether we're in an interactive session? -Levent.