On 07-Oct-1999, Adrian Hey <[EMAIL PROTECTED]> wrote:
> This is another reason I'm sceptical about referential transparency in
> any functional system of IO (streams, monads, continuations, world as value..)
> It is hard to sensibly define interaction between a timeless universe
> of pure functions and values and a real universe which continually evolves
> in real time. A state transformer method is about as good as you'll
> get, but this requires that somehow the times of future events is
> information which is embedded in the whatever state the program last left
> the universe in. Perhaps some people believe this, but I don't think
> the world works this way. (And even if this were true, unless we had
> some systematic way of extracting this information and predicting the
> future, it won't help us at all.)
Whether or not the world "really" works that way, the point is that we
can model it that way, and the world's behaviour matches the predictions
of our model.
Modelling it this way does help, even if we don't know the full contents
of the "StateOfUniverse" argument in any particular case,
because it allows us to apply mathematical reasoning to the behaviour
of our programs and their effects on the world.
When we say that something is _not_ referentially transparent, it means
that we can't reason about it directly using the usual techniques of
equational reasoning.
--
Fergus Henderson <[EMAIL PROTECTED]> | "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh> | of excellence is a lethal habit"
PGP: finger [EMAIL PROTECTED] | -- the last words of T. S. Garp.
