On 30 December 2011 16:59, Gregg Reynolds <d...@mobileink.com> wrote:
> > 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. >> > > > > time t: f 42 (computational process implementing func application > begins…) > t+1: <keystroke> = 1 > t+2: 43 (… and ends) > > time t+3: f 42 > t+4: <keystroke> = 2 > t+5: 44 > > Conclusion: f 42 != f 42 > > (This seems so extraordinarily obvious that maybe Heinrich has something > else in mind.) > > This seems such an obviously incorrect conclusion. f42 is a funtion for returning a program for returning an int, not a function for returning an int.
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