Roc doesn't allow side effects. All effects are wrapped and returned from a function. So this is just as pure as haskell. Though it may not be exposed in the same way as haskell, effects still boil down to something akin to monads and callbacks.

Honestly it looks like basically the same as getline/putStrLen from the tutorial(1) in the link below, just not written in an intentionally obtuse language.

Considering how much more approachable this Roc documentation/naming is, I'm wondering if it isn't so that the people writing Wikipedia's math pages are probably the same people that are drawn to and writes Haskell/monad "tutorials".

1: http://learnyouahaskell.com/input-and-output