One would argue that both are flawed because they are, in essence, a function which is not espressing itself clearly and cleanly. You are co-mingling state with

One would argue that both are flawed because they are, in essence, a function which is not espressing itself clearly and cleanly. You are co-mingling state with computation in a way that obscures and loses the advantages therein. If you want to make an example of something, then use a Reader, such that you are abstracting away the "source" of what is read and the side-effects thereof. Or an expiring cache (which is a good example of mutable state.) Or a mixed Reader which "reads" from either a cache or in the case of passing the expiration mark on the "key," some unknown "source."