[Haskell-cafe] How to make cabal pass flags to happy?

Hi all, I want to do something I thought would be quite simple, but try as I might I can't find neither information nor examples on how to achieve it. What I want specifically is to have happy produce a GLR parser from my .ly file, and I want this to happen during 'cabal install'. Which in turn means I want cabal to pass the "--glr" flag to happy during setup. My best guess is that I might want to use 'ppHappy' [1], or something in the vicinity, but there's no documentation for the combinator and it's far from obvious how to pass arguments to it. ... help? :-) Cheers, /Niklas