parseFile :: Parser (Maybe FilePath)
parseFile = optional $ option str $ mconcat
    [ short 'o'
    , help "Output file"
    , metavar "FILE"
    ]
parseFile :: Parser (Maybe FilePath)
parseFile = optional $ option str $ mconcat
    [ short 'o'
    , help "Output file"
    , metavar "FILE"
    ]
parseFile = optional $ option str $ mconcat
    [ short 'o'
    , help "Output file"
    , metavar "FILE"
    ]