hasCallback :: BC -> [(FDesc, Reg)]
hasCallback (FOREIGNCALL l rty (FStr fn) args) = filter isFn args
    where
        isFn (desc,_) = case toFType desc of
                            FFunction -> True
                            FFunctionIO -> True
                            _ -> False
hasCallback :: BC -> [(FDesc, Reg)]
hasCallback (FOREIGNCALL l rty (FStr fn) args) = filter isFn args
    where
        isFn (desc,_) = case toFType desc of
                            FFunction -> True
                            FFunctionIO -> True
                            _ -> False
hasCallback (FOREIGNCALL l rty (FStr fn) args) = filter isFn args
    where
        isFn (desc,_) = case toFType desc of
                            FFunction -> True
                            FFunctionIO -> True
                            _ -> False