[Haskell-cafe] Replacing IO with pure values

Hello all, in order to nail down my problem state in "Replacing the world in a State Machine with IO", I'd like to answer a much simpler question: If I have function which reads IO and I want to test this function by passing it a series of pure values, how would I do this? I suppose I can do this by splitting my function in two, such that the outer function does IO and the inner is a pure function. Is there any other way?