> Purity doesn’t mean that effects don’t happen. It means that effects don’t happen as a side effect of mere expression evaluation. I don't disagree? I was add

> Purity doesn’t mean that effects don’t happen. It means that effects don’t happen as a side effect of mere expression evaluation. I don't disagree? I was adding color to your explanation for other readers, not attempting to correct you. The evaluation of a program merely reduces or simplifies it, transforming its structure without adding or removing information. When we can't reduce further without interacting with the environment, something else must mediate that interaction. > That would be equally true of a programming model where every program is a pure function from a list of input lines to a list of output lines. Indeed, Haskell used this model (`[Request] -> [Response]`) before switching to use an IO monad. It made for a poor architectural basis for complex programs.