Tweeting a Blog Post via command line

tweet :: String -> FilePath -> IO ()
tweet creds path =
--          ^ Blog post we want to tweet about.
--    ^ Twitter API credentials.
  parseYamlFrontmatter <$> Data.ByteString.readFile path
--                         ^ Read the blog post.
-- ^ Parse the frontmatter of the blog post.
    >>= \case
      Done _post frontmatter ->
--    ^ If the frontmatter was parsed successfully..
        basicTweet (mkTweet path frontmatter) creds >> pure ()
--      ^ ..then tweet..
      e ->
        error $ show e
--      ^ ..else stop execution and display the error `e`.

data Front =
  Front
    { title :: String
    , description :: String
    , tags :: [String]
    } deriving (Show, Generic, FromJSON)

mkTweet :: FilePath -> Front -> String
mkTweet path Front{..} = fold [title, " 📒 ", description, "\n\n", htags, "\n\n", url]
--                ^ Same as `{ title = title, description = description, tags = tags }`
--                  but using two characters ;)
--                       ^ Fold strings to a single one.
--                         See previous post for a more sophisticated explanation!
  where
    base = "https://odone.io/posts"
    name = System.FilePath.Posix.takeBaseName path
    url = fold [base, "/", name, ".html"]
--  ^ Address to the blog post on odone.io.
    htags = Data.List.intercalate " " $ fmap ('#':) tags
--  ^ List of hashtags generated by appending '#'.
      in front of each tag coming from the frontmatter.

data Opts =
--   ^ The input we expect from the command line.
  Opts
    { creds :: String
    , post :: String
    }

main :: IO ()
main = do
  cs <- fmap (<> "/.cred.toml") getHomeDirectory
-- ^ Default path to the Twitter credentials file. See tweet-hs's docs for more info.
  execParser (opts cs) >>= (\Opts{..} -> tweet creds post)
-- ^ Parse the command line input and..
--  ..if successful then call `tweet`..
--  ..else show an error message and a summary on how to use the script correctly.
  where
    opts cs = info (parser cs <**> helper)
      (  fullDesc
      <> progDesc "Shares on Twitter a new blog POST using CREDS for authentication"
      )

parser :: FilePath -> Options.Applicative.Parser Opts
parser creds = Opts
      <$> strOption
         (  long "creds"
         <> metavar "CREDS"
         <> help "Path to creds .toml file"
         <> value creds
--          ^ `--creds` is optional and will use `~/.cred.toml` if not passed as input.
         <> showDefault
         )
      <*> argument str
--        ^ `post` is mandatory and the only argument to the script.
         (  metavar "POST"
         <> help "Path to blog post file"
         )

$ ./tweet.hs
#
# Missing: POST
#
# Usage: tweet.hs [--creds CREDS] POST
#   Shares on Twitter a new blog POST using CREDS for authentication

$ ./tweet.hs --help
#
# Usage: tweet.hs [--creds CREDS] POST
#   Shares on Twitter a new blog POST using CREDS for authentication
#
# Available options:
#   --creds CREDS            Path to creds .toml
#                            file (default: "/Users/rysiek/.cred.toml")
#   POST                     Path to blog post file
#   -h,--help                Show this help text