Another example: UNIX text tools. You can open a text in a editor (e.g. vim or emacs) and modify it in imperative style, or you can use cat, cut, sed, paste, jo

Another example: UNIX text tools. You can open a text in a editor (e.g. vim or emacs) and modify it in imperative style, or you can use cat, cut, sed, paste, join, and many other tools, which can operate on text, in stream mode, when original text is not modified. Text stream is monad here. Or you can convert (lift) your data to JSON or XML, and use JSON or XML tools in stream mode (e.g. when every record is on it own line): JSON and XML streams will be monads in such case. It's up to you to modify text manually, or use existing tools for text stream monad.