Tom Schrijvers wrote:
On Thursday 21 June 2007, Tom Schrijvers wrote:
That wouldn't make a difference. If, from the pure Haskell point of view we can't tell the difference between two expressions that denote the same function, then operations in the IO monad should not be able to do so either.
IO cannot be understood by denotational semantics ("=") alone anyway. I mean, we obviously have randomIO = randomIO but operationally ("~>"), we have a non-deterministic choice of transition randomIO ~> return 42 randomIO ~> return 13
John Cast wrote
This doesn't make any sense to me. IO is a non-determinism monad (among many other things). That's already true --- randomIO is one example; Control.Exception.evaluate is another (and is already dependent on the particular compilation choices made). I think of Haskell `values' as sets of legal representations anyway --- why shouldn't serialize be free to make a non-deterministic choice from among those sets, just like evaluate can make a non-deterministic choice from the set of exceptions an expression can throw?
Good point. I agree, if the specification is non-deterministic, this should be alright.
Yes, the only guarantee you can get is that "compile" can turn your serialization back into the same function: fmap compile . serialize = return . Just To illustrate the point, here's a serialize for integers: serialize :: Int -> IO String serialize n = do k <- randomRIO (1,n-1) return $ "(" ++show k ++ "+" ++ show (n-k) ++ ")" that gives intentionally different representations. Regards, apfelmus