On Fri, Dec 30, 2011 at 12:49 AM, Heinrich Apfelmus < apfel...@quantentunnel.de> wrote:
> > The function > > f :: Int -> IO Int > f x = getAnIntFromTheUser >>= \i -> return (i+x) > > is pure according to the common definition of "pure" in the context of > purely functional programming. That's because > > f 42 = f (43-1) = etc. > > Put differently, the function always returns the same IO action, i.e. the > same value (of type IO Int) when given the same parameter. > Two questions trouble me: How can we know whether this claim is true or not? What does the claim even mean, i.e., what does "the same IO action" mean, considering that we lack a denotational model of IO? - Conal
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