Magical Monoids

Recently something caught my eye while hacking on a Haskell project. Pay attention to the mempty in the code fragment below: readTextFileUtf8 :: FilePath -> IO (Either Utf8Error T.Text) readTextFileUtf8 filename = {- ... -}-- | Return "" in case of errors lenientReadTextFileUtf8 :: FilePath -> IO T.Text lenientReadTextFileUtf8 filename = do result <- readTextFileUtf8 filename pure $ either (\_ ->

[igrep]

ふらっとmemptyって書かれてるとどのMonoidインスタンスか分からなくなる問題、あるあるだよなぁ…