[michaelochurch]

Welcome to Haskell.

No, seriously. We allow side effects. We have the STM monad, the ST (single-threaded) monad, and the IO monad if you really want to go wild. And almost no one seriously argues that the IO monad is "dirty" and should be avoided. In fact, the type signature of a top-level executable's main is IO () by mandate.

I want to make a proposal, which is that we ban the term "side effect". It doesn't mean what people think it does.

For example, the print function puts output on the console but that's not a "side effect"; that's the main effect. I would argue also that non-detectable stateful effects (e.g. building up a large dictionary mutably) shouldn't be called "side effects" (although they are stateful effects) if they're purely implementation details that are hidden behind an interface.

"Side effect", I think, is a case of a term that used to resemble either a design flaw or a non-intuitive behavior (i.e. reading your command-line arguments deletes the strings, which is something that I encountered in one system) that is tolerated for performance's sake; but that has now been expanded to include stateful main (i.e. desired) effects as well.

[tome]

"Side effect" means something that happens implicitly as a result of evaluation. There's no need to ban the term; we just need to keep in mind how it differs from the more general notion of "effect".