Another example: Caching of results, transparent to the user of your function. If your function is otherwise pure you can simply use its parameter and hash them

Another example: Caching of results, transparent to the user of your function. If your function is otherwise pure you can simply use its parameter and hash them for a key to your result index. Examples where I've used this: Caching of regex results, replacing file reads with modification date polls and read from cache if not changed..