They can still have side-effects like non-termination.

But I didn't mean purity in that formal sense. I meant that Haskell is plenty pragmatic in its design.

To me, "pure" means referential transparency: same input, same output. So an `Int -> Int` function will return same result on same argument. So, similar to `Int -> IO Int`, the function (action) will return an Int after interacting with outside world, `IO` tracking the fact that this is the case.

Lambda calculus is as pure as can be, and also has terms that don't normalize. That is not considered a side effect.

A better example of impurity in Haskell for pragmatic's sake is the trace function, that can be used to print debugging information from pure functions.

> Lambda calculus is as pure as can be, and also has terms that don't normalize. That is not considered a side effect.

Many typed lambda calculi do normalise. You can also have a look https://dhall-lang.org/ for some pragmatic that normalises.

> A better example of impurity in Haskell for pragmatic's sake is the trace function, that can be used to print debugging information from pure functions.

Well, but that's just unsafePerformIO (or unsafePerformIO-like) stuff under the hood; that was already mentioned.

> They can still have side-effects like non-termination.

you can still have total functions that don't finish in humanly/business reasonable amount of time.

Yes?

Just like pure functions can use more memory than your system has. Or computing them can cause your CPU to heat up, which is surely a side-effect.

what does that have to do with purity?