lookupDependencies :: FilePath -> FilePath -> Action (FilePath, [FilePath])
lookupDependencies depFile file = do
    deps <- lookupValues depFile file
    case deps of
        Nothing -> error $ "No dependencies found for file " ++ quote file
        Just [] -> error $ "No source file found for file " ++ quote file
        Just (source : files) -> return (source, files)
lookupDependencies :: FilePath -> FilePath -> Action (FilePath, [FilePath])
lookupDependencies depFile file = do
    deps <- lookupValues depFile file
    case deps of
        Nothing -> error $ "No dependencies found for file " ++ quote file
        Just [] -> error $ "No source file found for file " ++ quote file
        Just (source : files) -> return (source, files)
lookupDependencies depFile file = do
    deps <- lookupValues depFile file
    case deps of
        Nothing -> error $ "No dependencies found for file " ++ quote file
        Just [] -> error $ "No source file found for file " ++ quote file
        Just (source : files) -> return (source, files)