{- |Have an output file (-o) been given? -}
output :: [Flag] -> Maybe FilePath
output xs = case [f | Output f <- xs] of
             [f] -> Just f
             _   -> Nothing  
output :: [Flag] -> Maybe FilePath
output xs = case [f | Output f <- xs] of
             [f] -> Just f
             _   -> Nothing  
output xs = case [f | Output f <- xs] of
             [f] -> Just f
             _   -> Nothing  