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

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.