 | Get the last CommentId this CommentId was rethreaded to, if it was.
fetchCommentRethreadLastDB :: CommentId -> DB (Maybe CommentId)
fetchCommentRethreadLastDB comment_id = go Nothing comment_id
  where
    go mlast_comment comment = do
        mnew_comment <- fetchCommentRethreadDB comment
        case mnew_comment of
            Nothing          -> return mlast_comment
            Just new_comment -> go mnew_comment new_comment

-- | Get a Comment's CommentTags.
f
fetchCommentRethreadLastDB :: CommentId -> DB (Maybe CommentId)
fetchCommentRethreadLastDB comment_id = go Nothing comment_id
  where
    go mlast_comment comment = do
        mnew_comment <- fetchCommentRethreadDB comment
        case mnew_comment of
            Nothing          -> return mlast_comment
            Just new_comment -> go mnew_comment new_comment

-- | Get a Comment's CommentTags.
fetchCommentRethreadLastDB comment_id = go Nothing comment_id
  where
    go mlast_comment comment = do
        mnew_comment <- fetchCommentRethreadDB comment
        case mnew_comment of
            Nothing          -> return mlast_comment
            Just new_comment -> go mnew_comment new_comment

-- | Get a Comment's CommentTags.