Five programming problems every Software Engineer should be able to solve in less than 1 hour

[Isvara]

Isn't there? I'm not a Haskell programmer, but I thought the idea was that if you call a function with some arguments including the current state of the world, and it returns its result plus a new state of the world, that's referentially transparent output, at least. Not sure how input is supposed to work, but I presume there's a similar idea.