On 11 Aug 2010, at 12:39, Ertugrul Soeylemez wrote: > Martijn van Steenbergen <mart...@van.steenbergen.nl> wrote: > >> On 8/2/10 7:09, Ertugrul Soeylemez wrote: >>> Given the definition of a Haskell function, Haskell is a pure >>> language. The notion of a function in other languages is not: >>> >>> int randomNumber(); >>> >>> The result of this function is an integer. You can't replace the >>> function call by its result without changing the meaning of the >>> program. >> >> I'm not sure this is fair. It's perfectly okay to replace a call >> "randomNumber()" by that method's *body* (1), which is what you argue >> is okay in Haskell. > > This is not the same. In Haskell you can replace the function call by > its /result/, not its body. You can always do that. But the result of > an IO-based random number generator is an IO computation, not a value. > It's not source code either, and it's not a function body. It's a > computation, something abstract without a particular representation.
It's still rather papering over the cracks to call this pure though. The IO based computation itself still has a result that you *can't* replace the IO based computation with. The fact that it's evaluated by the runtime and not strictly in haskell may give us a warm fuzzy feeling inside, but it still means we have to watch out for a lot of things we don't normally have to in a "very pure"[1] computation. Bob [1] Bob's arbitrary definition 1 – very pure computations are ones which can be replaced with their result without changing the behavior of the program *even* if said result is computed in the runtime and not by the Haskel program._______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
